Piezoelectric single crystal-polycrystalline ceramic composite, its manufacturing method, and piezoelectric and dielectric application parts using the same

Abstract

This article relates to a piezoelectric single crystal-polycrystalline ceramic composite, a manufacturing method thereof, and piezoelectric and dielectric application components using the piezoelectric single crystal-polycrystalline ceramic composite. The piezoelectric single crystal-polycrystalline ceramic composite is formed by optimizing the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and the volume fraction of the piezoelectric single crystal. This composite not only retains the excellent piezoelectric properties of the piezoelectric single crystal, but also enables mass production and reduces manufacturing costs. Therefore, the piezoelectric single crystal-polycrystalline ceramic composite can be used in piezoelectric application components and dielectric application components, including ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, field emission transducers, and field-vibration emission transducers, and can improve piezoelectric properties and cost competitiveness.

Description

Technical Field

[0001] The present invention relates to a piezoelectric single crystal - polycrystalline ceramics composite, a method for manufacturing the same, and piezoelectric and dielectric application components using the same. More specifically, it relates to a composite in which a piezoelectric single crystal having a high piezoelectric charge constant (d 33 ) and a low dielectric loss (Tanδ) is combined with polycrystalline ceramics particles. By optimizing the particle size distribution between the particles and the volume fraction of the piezoelectric single crystal and then combining them, the high piezoelectric properties of the piezoelectric single crystal are maintained, the mechanical brittleness characteristics are improved, and the production process is simplified so that mass production is possible. The present invention relates to a piezoelectric single crystal - polycrystalline ceramics composite, a method for manufacturing the same, and piezoelectric and dielectric application components using the same.

Background Art

[0002] Piezoelectric single crystals having a perovskite crystal structure ([A][B]O 3 ) exhibit much higher dielectric constants (K 3 T ), piezoelectric charge constants (d 33 ), and electromechanical coupling coefficients (k 33 ) compared to existing piezoelectric polycrystalline materials. They are used in high - performance components such as piezoelectric actuators, ultrasonic transducers, piezoelectric sensors, and dielectric capacitors, and are also expected to be used as substrate materials for various thin - film elements.

[0003] Among the piezoelectric single crystals having a perovskite crystal structure developed to date, there are PMN - PT (Pb(Mg 1 / 3 Nb 2 / 3 )O 3 -PbTiO 3 ), PZN - PT (Pb(Zn 1 / 3 Nb 2 / 3 )O 3 -PbTiO 3 ), PInN - PT (Pb(In 1 / 2 Nb 1 / 2 )O3 -PbTiO 3 )、 PYbN-PT (Pb(Yb 1 / 2 Nb 1 / 2 )O 3 -PbTiO 3 )、 PSN-PT (Pb(Sc 1 / 2 Nb 1 / 2 )O 3 -PbTiO 3 )、 BiScO 3 -PbTiO 3 (BS-PT), PMN-PInN-PT, and PMN-PYbN-PT, etc. Such single crystals exhibit congruent melting behavior during melting and are usually manufactured by existing single crystal growth methods such as the flux method and the Bridgman method.

[0004] However, the existing developed piezoelectric single crystals of PMN-PT and PZN-PT have the advantages of showing high dielectric and piezoelectric properties (K 3 T > 4,000, d 33 > 1,400 pC / N, k 33 > 0.85) at room temperature. However, due to disadvantages such as low phase transition temperatures (T C and T RT ), low electric field resistance (E C ), brittleness, and high manufacturing costs, the utilization of piezoelectric single crystals is quite limited.

[0005] Generally, piezoelectric single crystals with a perovskite crystal structure are known to have the highest dielectric and piezoelectric properties in the vicinity of the phase boundary between the rhombohedral crystal phase and the tetragonal crystal phase, that is, in the vicinity of the MPB (morphotropic phase boundary) composition. Tetragonal piezoelectric single crystals are known to be usable in some specific crystal directions with excellent piezoelectric or electro-optic properties.

[0006] However, since piezoelectric single crystals with a perovskite crystal structure generally exhibit the most excellent dielectric and piezoelectric properties when they are in the rhombohedral crystal phase, the application of piezoelectric single crystals in the rhombohedral crystal phase is the most active. However, piezoelectric single crystals in the rhombohedral crystal phase only exhibit stable behavior below the phase transition temperature (T RT ), so their use is possible only below T RT , which is the maximum temperature at which the rhombohedral crystal phase can exhibit stable behavior. Therefore, when the T RT phase transition temperature is low, the operating temperature of the piezoelectric single crystal in the rhombohedral crystal phase decreases, and the fabrication temperature and operating temperature of the piezoelectric single crystal application components are also limited to T RT or lower.

[0007] In addition, when the phase transition temperatures (T C and T RT ) and the coercive electric field (E C ) are low, the poling of the piezoelectric single crystal is likely to be removed (depoling) under machining, stress, heat generation, and driving voltage, resulting in the loss of excellent dielectric and piezoelectric properties. Therefore, piezoelectric single crystals with low phase transition temperatures (T C and T RT ) and coercive electric fields (E C ) have limitations in the fabrication conditions, operating temperature conditions, and driving voltage conditions of single crystal application components. In the case of PMN-PT single crystals, generally, T C <150 °C, T RT <80 °C, and E C <2.5 kV / cm. In the case of PZN-PT single crystals, generally, T C <170 °C, T RT <100 °C, and E C <3.5 kV / cm. Also, dielectric and piezoelectric application components fabricated from such piezoelectric single crystals have limitations in manufacturing conditions, operating temperature ranges, and operating voltage conditions, which have become obstacles to the development and practical application of piezoelectric single crystal application components.

[0008] To overcome the disadvantages of piezoelectric single crystals, single crystals with new compositions such as PInN-PT, PSN-PT, and BS-PT have been developed, and mixed single crystal compositions such as PMN-PInN-PT and PMN-BS-PT have also been studied.

[0009] However, in the case of such single crystals, it is impossible to simultaneously improve the dielectric constant, piezoelectric charge constant, phase transition temperature, electric field resistance, and mechanical properties, etc. Piezoelectric single crystals composed of compositions mainly containing expensive elements such as Sc and In have been an obstacle to the practical application of single crystals due to the high manufacturing cost of single crystals.

[0010] The reasons why piezoelectric single crystals with a perovskite crystal structure including PMN-PT developed so far show a low phase transition temperature can be roughly divided into three. First, it is that the phase transition temperature of relaxors (such as PMN and PZN) that are the main constituent components together with PT is low.

[0011] Non-Patent Document 1 presents the phase transition temperature (T C ) between the tetragonal phase and the cubic phase of polycrystalline piezoelectric ceramics with a perovskite structure in Table 1. Since the Curie temperature of the piezoelectric single crystal is almost the same as that of the polycrystalline body with the same composition, the Curie temperature of the piezoelectric single crystal can be estimated from the Curie temperature of the polycrystalline body.

[0012] Second, the MPB where the tetragonal phase and the rhombohedral phase form a boundary is not perpendicular to the temperature axis but gently inclined. In order to increase the phase transition temperature (T RT ) between the rhombohedral phase and the tetragonal phase, a decrease in the Curie temperature (T C ) is inevitable. Therefore, it has been difficult to simultaneously increase the Curie temperature (T C ) and the phase transition temperature (T RT ) between the rhombohedral phase and the tetragonal phase.

[0013] Third, when relaxors (such as PYbN, PInN, and BiScO 3 ) with a relatively high phase transition temperature are mixed into PMN-PT, etc., the phase transition temperature does not simply increase proportionally to the composition, or problems such as a decrease in dielectric and piezoelectric properties occur.

[0014] Furthermore, the relaxor-PT single crystals presented in Non-Patent Document 1 are manufactured mainly by the flux method and the Bridgman method, which are existing single crystal growth methods using a melting process. However, due to reasons in the manufacturing process of single crystals, it is difficult to manufacture large single crystals with uniform composition, the manufacturing cost is high, and mass production is difficult. Therefore, it has not yet been successfully commercialized.

[0015] In general, piezoelectric ceramic single crystals have lower mechanical strength and fracture toughness than piezoelectric ceramic polycrystals, so they have the drawback of being easily broken even by a small mechanical impact. Such brittleness of piezoelectric single crystals easily induces the fracture of piezoelectric single crystals during the production and use of application parts using piezoelectric single crystals, which has been a major limitation in the use of piezoelectric single crystals. Therefore, for the commercialization of piezoelectric single crystals, it is necessary to improve the mechanical properties of piezoelectric single crystals in addition to improving the dielectric and piezoelectric properties of piezoelectric single crystals.

[0016] On the other hand, Patent Document 1 is an invention related to the Solid-state Single crystal Growth [SSCG] Method. Different from the conventional liquid-phase single crystal growth method, without using a melting process and without special equipment, by controlling abnormal grain growth occurring in polycrystals through a general heat treatment process, single crystals of various compositions can be manufactured by the solid-state single crystal growth method, reducing the manufacturing cost of single crystals, and presenting a single crystal growth method capable of mass-producing single crystals with high reproducibility and economically.

[0017] In addition, Patent Document 2 uses the solid-state single crystal growth method to obtain a high dielectric constant (K 3 T ), a high piezoelectric constant (d 33 and k 33 ), a high phase transition temperature (Curie temperature, T C ), a high coercive electric field (E C) and a piezoelectric single crystal having improved mechanical properties are disclosed. A piezoelectric single crystal manufactured by a solid-phase single crystal growth method compatible with mass production of single crystals develops a single crystal composition that does not contain expensive raw materials, enabling commercialization of piezoelectric single crystals.

[0018] However, generally, compared with piezoelectric polycrystalline ceramics, piezoelectric single crystals exhibit a high piezoelectric charge constant but have a low breakdown electric field and are easily depolarized, resulting in low electrical stability and being limited in actual use. Therefore, although methods for increasing the breakdown electric field of piezoelectric single crystals have been proposed, the increase in the breakdown electric field has still been pointed out to have low practical effectiveness due to the problem of a decrease in piezoelectric properties.

[0019] Recently, research results and patents, etc., have been published on changing the composition of piezoelectric polycrystalline ceramics (such as addition of Sm, etc.) to epoch-makingly increase the piezoelectric charge constant [Non-Patent Document 2].

[0020] In this case, although it has been successful in increasing the piezoelectric charge constant (d 33 ) of piezoelectric polycrystalline ceramics to 1,000 [pC / N] or more, the phase transition temperature between ferroelectric phases (such as rhombohedral phase and tetragonal phase) and the Curie temperature (T C ) have greatly decreased, and the dielectric loss (Tanδ) has greatly increased, still greatly limiting its application to general piezoelectric application fields. Therefore, in order to enable practical applications, it is essential to develop piezoelectric ceramics having a high piezoelectric charge constant, a high phase transition temperature, and a low dielectric loss (tanδ).

[0021] However, in general piezoelectric polycrystalline ceramics, the matrix particles are arranged in random directions and do not exhibit high piezoelectric properties like piezoelectric single crystals.

[0022] To solve such problems, in polycrystalline ceramics, a Templated Grain Growth process has been proposed to align the directions of particles in the characteristic direction. In the existing Templated Grain Growth process, seed single crystals of a specific shape (e.g., thin plate shape) are aligned in a specific direction inside the polycrystal, and heat treatment is performed to grow the seed single crystals in a specific direction to produce ceramics with crystal orientation. In this case, the seed single crystals either remain inside the grown crystal-oriented particles or disappear due to the reaction.

[0023] In the case of the crystal-oriented ceramics produced by the crystal orientation growth process, it has been confirmed that they exhibit relatively high piezoelectric properties compared to general polycrystalline ceramics. However, the process cost of manufacturing seed single crystals of a specific shape suitable for the crystal orientation growth process is extremely high. As a result, due to the high manufacturing cost and difficulty in mass production of crystal-oriented ceramics, there are difficulties in commercialization.

[0024] Therefore, there is a need for a process that does not use seed single crystals of a specific shape and the seed single crystal alignment process, simplifies the manufacturing process, reduces the manufacturing cost, and enables mass production.

[0025] Here, the inventor has made efforts to improve the conventional problems. As a result, despite excellent piezoelectric properties, due to the difficulty in mass production and high manufacturing process cost, a piezoelectric single crystal with limited various applications is combined with polycrystalline ceramic particles. However, the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and the volume fraction of the piezoelectric single crystal are optimized to maintain the high piezoelectric properties of the piezoelectric single crystal and improve the mechanical properties of suppressing brittleness while simplifying the production process to enable mass production, providing a piezoelectric single crystal - polycrystalline ceramic composite. By confirming the physical properties of the piezoelectric single crystal - polycrystalline ceramic composite, the present invention has been completed.

Prior Art Documents

Patent Documents

[0026]

Patent Document 1

Patent Document 2

Non-Patent Document

[0027]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0028] An object of the present invention is to provide a piezoelectric single crystal - polycrystalline ceramic composite.

[0029] Another object of the present invention is to provide a method for manufacturing a piezoelectric single crystal - polycrystalline ceramic composite.

[0030] Still another object of the present invention is to provide piezoelectric application parts and dielectric application parts using the piezoelectric single crystal - polycrystalline ceramic composite.

Means for Solving the Problems

[0031] In order to achieve the above-described objects, the present invention provides a perovskite structure ([A][B]O 3) A composite in which a piezoelectric single crystal and polycrystalline ceramic particles are combined, wherein the average particle size distribution (a) of the piezoelectric single crystal is 100 to 1,000 μm, the average particle size distribution (b) of the polycrystalline particles is 2 to 20 μm, and the particle size distribution a / b is 20 to 100, to provide a piezoelectric single crystal - polycrystalline ceramic composite.

[0032] In the piezoelectric single crystal - polycrystalline ceramic composite, the piezoelectric single crystal is preferably contained in an amount of 30 to 80% by volume, and in the composite, the piezoelectric single crystal is oriented in a specific crystal direction. Preferably, the specific crystal direction of the piezoelectric single crystal is the <001> or <011> direction.

[0033] The piezoelectric single crystal - polycrystalline ceramic composite in which the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and the contained volume ratio of the piezoelectric single crystal are optimized and combined has, under normal temperature conditions, (1) a dielectric constant (Dielectric Constant, K 3 T ) of 3,000 or more, (2) a piezoelectric charge constant (Piezoelectric Charge Constant, d 33 ) of 1,200 pC / N or more, and (3) the first - shown phase transition temperature of 80°C or more, maintaining the high piezoelectric properties of the piezoelectric single crystal and improving the mechanical properties of suppressing brittleness.

[0034] The piezoelectric single crystal - polycrystalline ceramic composite of the present invention has a phase transition between ferroelectric phases (such as rhombohedral phase and tetragonal phase) below the Curie temperature (T C ), and the dielectric constant (K 3 T ) of the piezoelectric single crystal - polycrystalline ceramic composite is more than three times higher than that at normal temperature at the phase transition temperature between ferroelectric phases.

[0035] Also, the piezoelectric charge constant (Piezoelectric Charge Constant, d 33, the ratio [d 33 / tanδ] of the piezoelectric charge constant (d 33 , pC / N) and the dielectric loss (tanδ (%)) is 1,000 or more, and the piezoelectric charge constant (d 33 , pC / N), piezoelectric voltage constant (Piezoelectric Voltage ConsTant, g -3 , 10 33 Vm / N)) and the dielectric loss (Tanδ%) ratio [(d 33 ×g

[0036] In the piezoelectric single crystal - polycrystalline ceramics composite of the present invention, the piezoelectric single crystal is a perovskite - type structure ([A][B]O 3 ) piezoelectric single crystal, and preferably, it is a piezoelectric single crystal having the composition formula of Chemical Formula 1 below.

[0037] Chemical Formula 1 [A 1-(a+1.5b) B a C b [[(MN) 1-x-y (L) y Ti x O 3-z In the above formula, A is Pb or Ba, B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn, and Sr, C is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, L is in a single or mixed form selected from Zr or Hf, M is at least one selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb, and Zn, N is at least one selected from the group consisting of Nb, Sb, Ta, and W, 0 < a ≤ 0.10, 0 < b ≤ 0.05, 0.05 ≤ x ≤ 0.58, 0.05 ≤ y ≤ 0.62, and 0 ≤ z ≤ 0.02.

[0038] The piezoelectric single crystal having the composition formula of Chemical Formula 1 preferably has a porosity in the single crystal of 0.5 vol% or more.

[0039] The piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention has a composition satisfying 0.01 ≦ a ≦ 0.10 and 0.01 ≦ b ≦ 0.05, and more preferably, in the above formula, a / b ≧ 2 is satisfied.

[0040] The piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention more preferably satisfies 0.10 ≦ x ≦ 0.58 and 0.10 ≦ y ≦ 0.62.

[0041] In the piezoelectric single crystal, when L is in a mixed form, it has the composition formula of the following Chemical Formula 2 or Chemical Formula 3.

[0042] Chemical Formula 2 [A 1-(a+1.5b) B a C b [(MN) 1-x-y (Zr 1-w ,Hf w ) y Ti x O 3 Chemical Formula 3 [A 1-(a+1.5b) B a C b [[(MN) 1-x-y (Zr 1-w ,Hf w ) y Ti x O 3-z In the above formula, A, B, C, M, N, a, b, x, y, and z are the same as those in Chemical Formula 1 or 2, provided that 0.01 ≦ w ≦ 0.20 is shown.

[0043] At this time, the piezoelectric single crystal has a Curie temperature (T C ) of 180° C. or higher, and a phase transition temperature between the rhombohedral phase and the tetragonal phase (T RT) is 100 °C or higher, and the longitudinal electromechanical coupling coefficient (k 33 ) is 0.85 or higher, and the coercive electric field (E C ) satisfies 4 to 12 kV / cm.

[0044] In particular, the piezoelectric single crystal has a dielectric constant (K 3 T ) of 4,000 or more, preferably 4,000 to 15,000, and a piezoelectric charge constant (d 33 ) of 1,400 or more, preferably 1,400 to 6,000 pC / N.

[0045] The present invention is a method for manufacturing the piezoelectric single crystal - polycrystalline ceramics composite, comprising pulverizing a piezoelectric single crystal having a perovskite structure ([A][B]O 3 ) to 50 μm or more to prepare single crystal particles (a), preparing polycrystalline powder particles (b) having an average particle size distribution of 0.1 to 5 μm, mixing them so that the particle size distribution a / b becomes 20 or more, and performing heat treatment, growing the particle size of the piezoelectric single crystal to 100 μm or more by the heat treatment, After the heat treatment, a method for manufacturing a piezoelectric single crystal - polycrystalline ceramics composite is provided, which is performed so that the particle size distribution a / b becomes 20 to 100.

[0046] Before the heat treatment, in the mixing step, the piezoelectric single crystal is contained at 80% by volume or less, and after the heat treatment, the piezoelectric single crystal is contained in the range of 30 to 80% by volume of the single crystal.

[0047] Further, after the heat treatment, the average particle size distribution (a) of the grown piezoelectric single crystal is 100 μm or more, more preferably 100 to 1,000 μm, the average particle size distribution (b) of the grown polycrystalline particles is 2 to 20 μm, and a piezoelectric single crystal - polycrystalline ceramics composite that satisfies the requirement that the particle size distribution a / b is 20 to 100 is manufactured.

[0048] At this time, the heat treatment is preferably performed at 900 to 1,300 °C for 1 to 100 hours and at a heating rate of 1 to 20 °C / min.

[0049] Furthermore, the present invention provides piezoelectric application parts and dielectric application parts including the piezoelectric single crystal - polycrystalline ceramics composite.

[0050] Specifically, it can be applied to any one selected from the group consisting of ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, Electric Field Generating Transducers, and Electric Field and Vibration Generating Transducers including the piezoelectric single crystal - polycrystalline ceramics composite.

Advantages of the Invention

[0051] The piezoelectric single crystal - polycrystalline ceramics composite according to the present invention suppresses the dielectric properties of a piezoelectric single crystal having a dielectric constant (K 3 T ≥4,000) and a piezoelectric charge constant (d 33 ≥1,400 pC / N) without being suppressed inside the composite, and the dielectric and piezoelectric charge constant (d 33 ≥1,200 pC / N) of the piezoelectric single crystal - polycrystalline ceramics composite of the present invention is also highly preserved, and mass production is possible at a low process cost.

[0052] The piezoelectric single crystal - polycrystalline ceramics composite of the present invention has excellent piezoelectric properties and can be mass - produced at a low price, so it can satisfy the performance and price competitiveness of piezoelectric application parts and dielectric application parts using the same.

Brief Description of the Drawings

[0053]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0054] Hereinafter, the present invention will be described in detail.

[0055] The present invention relates to a perovskite - type structure ([A][B]O 3) A composite in which a piezoelectric single crystal and polycrystalline ceramic particles are combined. When (1) the difference in particle size between the piezoelectric single crystal and the polycrystalline ceramic particles is specified at an optimal ratio, the excellent piezoelectric properties of the piezoelectric single crystal are preserved. And (2) by optimizing the difference in composition between the piezoelectric single crystal and the polycrystalline ceramic particles, the piezoelectric and mechanical properties of the composite can be improved.

[0056] More specifically, in the piezoelectric single crystal - polycrystalline ceramic composite of the present invention, the average particle size distribution (a) of the piezoelectric single crystal is 100 to 1,000 μm, the average particle size distribution (b) of the polycrystalline particles is 2 to 20 μm, and the particle size distribution a / b is 20 to 100.

[0057] Also, the volume ratio of the piezoelectric single crystal to the polycrystalline ceramic particles is optimized so that the piezoelectric single crystal - polycrystalline ceramic composite of the present invention contains 30 to 80 volume% of the piezoelectric single crystal.

[0058] Generally, in the case of a composite in which a piezoelectric single crystal having a high piezoelectric charge constant (d 33 ≧1,400 pC / N) is combined with polycrystalline ceramic particles, the piezoelectric charge constant (d 33 ≦1,000 pC / N) tends to be significantly lower. However, such a level of composite has low practical application value.

[0059] In contrast, the present invention optimizes (1) the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles, and (2) the contained volume ratio of the piezoelectric single crystal, to maintain the high piezoelectric properties (piezoelectric charge constant, d 33 ≧1,200 pC / N) of the piezoelectric single crystal, and while improving the mechanical properties of suppressing brittleness, it is possible to provide a piezoelectric single crystal - polycrystalline ceramic composite that can be manufactured by simplifying the production process so as to enable mass production.

[0060] The piezoelectric single crystal has no special restrictions on its shape. However, in the matrix, in order to increase the packing density and thus increase the overall density of the composite, an isotropic shape such as a sphere or a regular hexahedron is preferred.

[0061] Also, in the composite, the piezoelectric single crystals may be arranged in random directions. However, preferably, when the piezoelectric single crystals are oriented in a specific crystal direction, the piezoelectric properties can be further improved. At this time, the specific crystal direction of the piezoelectric single crystal is the <001> or <011> direction.

[0062] Unlike the existing templated grain growth process, the piezoelectric single crystal of the present invention does not grow the piezoelectric single crystal using a specific seed single crystal inside the matrix. Therefore, the interior of the piezoelectric single crystal of the present invention does not contain the seed single crystal used for the growth of the single crystal or the seed single crystal that disappeared after the single crystal growth.

[0063] Therefore, the process cost for manufacturing a specific seed single crystal is omitted, the manufacturing process is simplified, the manufacturing cost is reduced, and mass production is possible.

[0064] However, during the process of mixing the piezoelectric single crystal grown externally with the polycrystalline ceramic powder and sintering the composite, the piezoelectric single crystal may grow partially, but this is not an essential process as in the existing templated grain growth process.

[0065] The piezoelectric single crystal - polycrystalline ceramic composite in which the particle size distribution between the piezoelectric single crystal and the polycrystalline ceramic particles and the volume fraction of the piezoelectric single crystal are optimized has [1] a dielectric constant (K 3 T ) of 3,000 or more at room temperature, [2] a piezoelectric charge constant (d33 ) is 1,200 pC / N or more, and has a characteristic that the phase transition temperature first shown at room temperature is 80°C or more.

[0066] In the above, room temperature means that physical property evaluation is performed under the same temperature conditions within the room temperature range. Unless otherwise specified in the specification of the present invention, room temperature means that it is performed at a temperature of 30°C.

[0067] More specifically, the piezoelectric single crystal - polycrystalline ceramics composite of the present invention shows a phase transition phenomenon between ferroelectric phases (such as rhombohedral phase and tetragonal phase) at or below the Curie temperature (T C ). Preferably, the dielectric constant (K 3 T ) of the piezoelectric single crystal has a characteristic that it is even higher than the Curie temperature (T C ) at the phase transition temperature between ferroelectric phases.

[0068] More preferably, the dielectric constant (K 3 T ) of the piezoelectric single crystal - polycrystalline ceramics composite has a characteristic that it is three times or more higher at the phase transition temperature between ferroelectric phases than at room temperature.

[0069] Also, generally, a piezoelectric single crystal has a high piezoelectric charge constant (d 33 ) and a low dielectric loss (Tanδ). In contrast, in the case of piezoelectric polycrystalline ceramics, the piezoelectric charge constant (d 33 ) and the dielectric loss (Tanδ) increase simultaneously, and it is difficult to develop polycrystalline piezoelectric ceramics having a high piezoelectric charge constant and a low dielectric loss (tanδ).

[0070] Here, in the present invention, the characteristics of a piezoelectric single crystal having a high piezoelectric charge constant (d 33 ) and a low dielectric loss (tanδ) are maximized, and the piezoelectric charge constant (d 33) is maximized and the dielectric loss (tanδ) is minimized, resulting in a characteristic where the ratio of the piezoelectric charge constant (Piezoelectric Charge Constant, d 33 , pC / N) to the dielectric loss (Dielectric Loss, Tanδ (%)) [= d 33 / Tanδ] is maximized to 1,000 or more.

[0071] Also, the piezoelectric single crystal - polycrystalline ceramic composite of the present invention has a small increase in the dielectric constant, and at room temperature, the piezoelectric charge constant (d 33 , pC / N), the piezoelectric voltage constant (Piezoelectric Voltage Constant, g 33 , 10 -3 Vm / N)) and the ratio of the dielectric loss (tanδ%) [(d 33 ×g 33 ) / Tanδ] are simultaneously maximized to 25,000 or more.

[0072] Also, in the piezoelectric single crystal - polycrystalline ceramic composite of the present invention, part or all of the empty space inside the composite may be filled with a polymer. In this case, flexible matrix materials such as polymers and epoxies inside the composite enable low - temperature molding of the composite and impart flexibility.

[0073] The piezoelectric single crystal used in the piezoelectric single crystal - polycrystalline ceramic composite of the present invention has a high dielectric constant (K 3 T ≧4,000), a piezoelectric charge constant (d 33 ≧1,400 pC / N), and an electric field resistance (E C ≧4~12 kV / cm).

[0074] More specifically, the piezoelectric single crystal used in the present invention is a piezoelectric single crystal having a perovskite - type structure ([A][B]O 3 ), and preferably, it is a piezoelectric single crystal having the composition formula of Chemical Formula 1 below.

[0075] Chemical Formula 1 [A 1-(a+1.5b) B a Cb [(MN) 1-x-y (L) y Ti x O 3-z In the above formula, A is Pb or Ba, B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn, and Sr, C is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, L is in a single or mixed form selected from Zr or Hf, M is at least one selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb, and Zn, and N is at least one selected from the group consisting of Nb, Sb, Ta, and W, 0 < a ≤ 0.10, 0 < b ≤ 0.05, 0.05 ≤ x ≤ 0.58, 0.05 ≤ y ≤ 0.62, and 0 ≤ z ≤ 0.02.

[0076] In the piezoelectric single crystal having the composition formula of Chemical Formula 1, it is preferable that the porosity in the single crystal is 0.5% by volume or more.

[0077] The piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention has a perovskite crystal structure ([A][B]O 3 ) in which the [A] site ions are composed of a composite composition based on the tendency that the piezoelectric properties further increase while the chemical composition is composite.

[0078] At this time, in the piezoelectric single crystal having the composition formula of Chemical Formula 1, specifically looking at the composite composition of the [A] site ions, [A 1-(a+1.5b) B a C b may be composed of, and the composition of the above A includes a leaded or lead-free element. In the examples of the present invention, although it is described by being limited to a lead-based piezoelectric single crystal in which A is Pb, it is not limited thereto.

[0079] In the above-mentioned [A] site ions, the B composition is at least one selected from the group consisting of divalent metal elements, preferably at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn, and Sr, and the C composition can be used as long as it is a trivalent metal element.

[0080] Preferably, it is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and more preferably, a lanthanum-based element is used in a single or mixed form of one or two kinds.

[0081] In the examples of the present invention, in the [A] site ions, the C composition is described as a single or at least one mixed composition containing Sm, but it is not limited thereto.

[0082] In the piezoelectric single crystal having the composition formula of Chemical Formula 1, in the composite composition of [A] site ions, [A corresponding to [A] site ions 1-(a+1.5b) B a C b The composition is characterized in that when A is a lead-based or lead-free piezoelectric single crystal, it is composed of a combination of a divalent metal element and a trivalent metal element as a requirement for realizing the target physical properties.

[0083] That is, it must satisfy 0.01 ≦ a ≦ 0.10 and 0.01 ≦ b ≦ 0.05, and more preferably, it satisfies a / b ≧ 2. At this time, in the above, if a is less than 0.01, there is a problem that the perovskite phase is unstable, and if it exceeds 0.10, the phase transition temperature becomes too low and it becomes difficult to use in practice, which is not preferable.

[0084] Also, if the requirement of a / b ≧ 2 is not satisfied, the dielectric and piezoelectric properties are not maximized, or the growth of the single crystal is restricted, which is not preferable.

[0085] At this time, in the piezoelectric single crystal having the composition formula of Chemical Formula 1, in the composite composition of [A] site ions, when it is a composite composition as compared with the case where it is composed of only a trivalent metal element or a divalent metal element, an excellent dielectric constant can be realized.

[0086] Generally known [A][MN]O 3 -PbTiO 3 -PbZrO 3 The phase diagram shows a composition region exhibiting excellent dielectric and piezoelectric properties around the phase boundary (MPB) between the rhombohedral crystal phase and the tetragonal crystal phase. [A][MN]O 3 -PbTiO 3 -PbZrO 3 In the phase diagram, the dielectric and piezoelectric properties are maximized in the phase boundary composition region between the rhombohedral crystal phase and the tetragonal crystal phase, and the dielectric and piezoelectric properties gradually decrease as the distance from the MPB composition region increases. And in the composition range within 5 mol% from the MPB composition region into the rhombohedral crystal phase region, the decrease in the dielectric and piezoelectric properties is small and very high dielectric and piezoelectric property values are maintained. Also, in the composition range within 10 mol% from the MPB composition region into the rhombohedral crystal phase region, the dielectric and piezoelectric properties continuously decrease, but show dielectric and piezoelectric property values high enough to be applied to dielectric and piezoelectric application parts. When the composition changes from the MPB composition region into the tetragonal crystal phase region, the dielectric and piezoelectric properties decrease more rapidly than when the composition changes into the rhombohedral crystal phase region. However, even in the case of the composition range within 5 mol% or within 10 mol% into the tetragonal stable region, the dielectric and piezoelectric properties continuously decrease, but show dielectric and piezoelectric property values high enough to be applied to dielectric and piezoelectric application parts.

[0087] PbTiO 3 and PbZrO 3 The phase boundary (MPB) between and PbTiO 3 :PbZrO 3 =x:y = 0.48:0.52 (molar ratio) is known.

[0088] When the composition changes by 5 mol% from the MPB composition region into the rhombohedral crystal phase region and into the tetragonal crystal phase region respectively, the maximum values of x and y are 0.53 and 0.57 respectively (in other words, when x is maximum, x:y = 0.53:0.47, and when y is maximum, x:y = 0.43:0.57). Also, when the composition changes by 10 mol% from the MPB composition region into the rhombohedral crystal phase region and into the tetragonal crystal phase region respectively, the maximum values of x and y are 0.58 and 0.62 respectively (in other words, when x is maximum, x:y = 0.58:0.42, and when y is maximum, x:y = 0.38:0.62). In the composition range within 5 mol% from the MPB composition region into the rhombohedral crystal phase region and into the tetragonal crystal phase region respectively, high dielectric and piezoelectric property values are maintained. Also, in the composition range within 10 mol% from the MPB composition region into the rhombohedral crystal phase region and into the tetragonal crystal phase region respectively, high dielectric and piezoelectric property values are shown which are sufficient for application to dielectric and piezoelectric application components.

[0089] Also, when the content of PbTiO 3 and PbZrO 3 , that is, when the values of x and y are 0.05 or less, it may not be possible to create a phase boundary between the rhombohedral crystal phase and the tetragonal crystal phase, or the phase transition temperature and the coercive field are too low to be suitable for the present invention.

[0090] In the chemical formula 1, x preferably belongs to the range of 0.05 ≤ x ≤ 0.58, and more preferably 0.10 ≤ x ≤ 0.58. At this time, when x is less than 0.05, the phase transition temperatures (T C and T RT ), the piezoelectric charge constant (d 33 , k 33 ), or the coercive field (E C ) are low, and when x exceeds 0.58, the dielectric constant (K 3 T ), the piezoelectric charge constant (d 33 , k 33 ), or the phase transition temperature (T RT) is low. On the other hand, y preferably belongs to the range of 0.050 ≦ y ≦ 0.62, more preferably satisfying 0.10 ≦ y ≦ 0.62. The reason is that when y is less than 0.05, the phase transition temperature (T C and T RT ), piezoelectric charge constant (d 33 , k 33 ) or the anti-electric field (E C ) is low, and when it exceeds 0.62, the dielectric constant (K 3 T ) or the piezoelectric charge constant (d 33 , k 33 ) is low.

[0091] The piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention contains a metal tetravalent element in the [B] site ion in the perovskite crystal structure ([A][B]O 3 ), but is particularly limited to a single or mixed form selected from Zr or Hf with respect to the L composition.

[0092] If it is the above mixed form, a piezoelectric single crystal having the composition formula of the following Chemical Formula 2 or Chemical Formula 3 is provided.

[0093] Chemical Formula 2 [A 1-(a+1.5b) B a C b [(MN) 1-x-y (Zr 1-w , Hf w ) y Ti x O 3 Chemical Formula 3 [A 1-(a+1.5b) B a C b [(MN) 1-x-y (Zr 1-w , Hf w ) y Ti x O 3-z In the above formula, A, B, C, M, N, a, b, x, y, and z are the same as those in Chemical Formula 1, provided that 0.01 ≦ w ≦ 0.20 is shown.

[0094] At this time, if w is less than 0.01, there is a problem that the dielectric and piezoelectric properties are not maximized. If it exceeds 0.20, the dielectric and piezoelectric properties will decrease rapidly, which is not preferable.

[0095] The piezoelectric single crystal having the composition formulas of Chemical Formula 1 to Chemical Formula 3 above has a perovskite crystal structure ([A][B]O 3 ). By combining the composite composition of [A] site ions and the composition of [B] site ions, the Curie temperature (T C ) is 180 °C or higher, and at the same time, the phase transition temperature between the rhombohedral phase and the tetragonal phase (T RT ) is a piezoelectric single crystal of 100 °C or higher. At this time, if the Curie temperature is less than 180 °C, there is a problem that it is difficult to raise the coercive electric field (E C ) to 5 kV / cm or higher or the phase transition temperature (T RT ) to 100 °C or higher.

[0096] Also, the piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention has a perovskite crystal structure ([A][B]O 3 ), and is characterized in that it is controlled to 0 ≤ z ≤ 0.02 with respect to the oxygen vacancy at the [O] site. At this time, if z exceeds 0.02, there is a problem that the dielectric and piezoelectric properties will rapidly decrease, which is not preferable.

[0097] When oxygen vacancies are induced in the above range, the coercive electric field and the internal electric field are effectively increased, and the stability of the piezoelectric single crystal is increased under electric field driving and mechanical load conditions. Therefore, the piezoelectric properties can be maximized and the stability can be enhanced at the same time.

[0098] The piezoelectric single crystal having the composition formula of Chemical Formula 1 according to the present invention has an electromechanical coupling coefficient (k 33 ) of 0.85 or more. If the electromechanical coupling coefficient is less than 0.85, the characteristics are similar to those of piezoelectric polycrystalline ceramics, and the energy conversion efficiency is low, which is not preferable.

[0099] The piezoelectric single crystal according to the present invention preferably has a breakdown electric field (E C ) of 4 to 12 kV / cm. If the breakdown electric field is less than 4 kV / cm, there is a problem that poling is easily removed during the processing of the piezoelectric single crystal or during the production or use of piezoelectric single crystal application parts.

[0100] Also, the piezoelectric single crystal according to the present invention simultaneously satisfies a high dielectric constant (K 3 T ≥4,000 to 15,000) and a high piezoelectric charge constant (d 33 ≥1,400 to 6,000 pC / N).

[0101] Also, the piezoelectric single crystal having the composition formula of Chemical Formula 1 of the present invention has a composition gradient inside the single crystal of 0.2 to 0.5 mol%, and can provide a uniform single crystal.

[0102] The composition of the piezoelectric single crystal may further contain a reinforcing second phase (P) of 0.1 to 20% by volume ratio. The reinforcing second phase P is a metal phase, an oxide phase, or a pore.

[0103] More specifically, the reinforcing second phase P is at least one selected from the group consisting of Au, Ag, Ir, Pt, Pd, Rh, MgO, ZrO 2 , and pores. The reinforcing second phase P is uniformly distributed in the form of particles or regularly distributed with a certain pattern in the piezoelectric single crystal.

[0104] In the piezoelectric single crystal, x and y belong to a range within 10 mol%, more preferably within 5 mol% of the composition of the morphotropic phase boundary (MPB) between the rhombohedral crystal phase and the tetragonal crystal phase.

[0105] Lead zirconate (PbZrO 3 ) not only has a high phase transition temperature of 230 °C but also has the effect of making the MPB more perpendicular to the temperature axis, enabling the development of a composition with a high rhombohedral crystal phase and tetragonal crystal phase transition temperature (T RT ) while maintaining a high Curie temperature, and T C and T RT can be simultaneously high.

[0106] Conventionally, even when lead zirconate is mixed into the composition of a piezoelectric single crystal, the phase transition temperature increases in proportion to the content of lead zirconate. Therefore, a piezoelectric single crystal with a perovskite crystal structure containing zirconium (Zr) or lead zirconate can overcome the problems of existing piezoelectric single crystals.

[0107] In addition, zirconia (ZrO 2 ) or lead zirconate is used as a main component in existing piezoelectric polycrystalline materials and is an inexpensive raw material, so the object of the present invention can be achieved without increasing the raw material price of the single crystal.

[0108] In contrast, a perovskite-type piezoelectric single crystal containing lead zirconate shows incongruent melting behavior during melting, unlike PMN-PT and PZN-PT, etc. Therefore, when showing incongruent melting behavior, during melting of the solid phase, it separates into a liquid phase and solid phase zirconia (solid phase ZrO 2 ), and the solid phase zirconia particles in the liquid phase interfere with single crystal growth, making it impossible to manufacture by general single crystal growth methods such as the flux method and the Bridgman method that use a melting process.

[0109] In general single crystal growth methods using a melting process, it is difficult to manufacture single crystals containing a strengthening second phase, and there has been no report on this yet. This is because the strengthening second phase is chemically unstable and reacts with the liquid phase at temperatures above the melting temperature, so it is impossible to maintain an independent second phase morphology and it disappears. Also, in the liquid phase, due to the density difference between the second phase and the liquid phase, separation between the second phase and the liquid phase occurs, making it difficult to manufacture single crystals containing the second phase. Furthermore, it is impossible to adjust the volume fraction, size, shape, arrangement, and distribution, etc. of the strengthening second phase inside the single crystal.

[0110] Therefore, the present invention manufactures a piezoelectric single crystal containing a strengthening second phase using a solid-phase single crystal growth method that does not use a melting process. In the solid-phase single crystal growth method, since the growth of the single crystal is carried out at a temperature below the melting temperature, the chemical reaction between the strengthening second phase and the single crystal is suppressed, and the strengthening second phase can stably exist in an independent shape inside the single crystal.

[0111] Also, the growth of the single crystal is carried out in a polycrystal containing a strengthening second phase, and during the growth of the single crystal, there are no changes in the volume fraction, size, shape, arrangement, and distribution, etc. of the strengthening second phase. Therefore, when adjusting the volume fraction, size, shape, arrangement, and distribution, etc. of the strengthening second phase inside the polycrystal and growing a single crystal in the process of making a polycrystal containing a strengthening second phase, as a result, it is possible to manufacture a single crystal containing a strengthening second phase with a desired shape, that is, a second phase-reinforced single crystal.

[0112] Therefore, conventionally, in the flux method and the Bridgman method, which are single crystal growth methods, the perovskite crystal structure ([A][B]O 3In (0), a piezoelectric single crystal cannot be produced with a composite composition. In particular, in the case of the flux method and the Bridgman method including a melting step, in the production process, the composition gradient inside the single crystal is produced at 1 to 5 mol% or more, whereas in the solid-phase single crystal growth method of the present invention, the composition gradient inside the single crystal may be produced with a uniform composition of 0.2 to 0.5 mol%.

[0113] Therefore, according to the present invention, by the solid-phase single crystal growth method, in a perovskite crystal structure ([A][B]O 3 ), even when the composite composition of the [A] site ions and the combination between the [B] site ions are complex compositions, by growing a piezoelectric single crystal uniformly, compared with a conventional piezoelectric single crystal, the dielectric constant (K 3 T ≥4,000 or more, preferably 4,000 to 15,000), the piezoelectric charge constant (d 33 ≥1,400 or more, preferably 1,400 to 6,000 pC / N), and a high breakdown electric field (E C ≥4 to 12 kV / cm) can be significantly increased, and a novel piezoelectric single crystal can be provided.

[0114] Further, the present invention pulverizes a piezoelectric single crystal of a perovskite structure ([A][B]O 3 ) to 50 μm or more to prepare single crystal particles (a), prepares polycrystalline powder particles (b) having an average particle size distribution of 0.1 to 5 μm, mixes them so that the particle size distribution a / b becomes 20 or more, and performs heat treatment, grows the piezoelectric single crystal to 100 μm or more in particle size by the heat treatment, and provides a method for producing a piezoelectric single crystal - polycrystalline ceramic composite body that is performed so that the particle size distribution a / b becomes 20 to 100 after the heat treatment.

[0115] The method for producing a piezoelectric single crystal of the present invention is performed by the solid-phase single crystal growth method (see Patent Documents 1 and 2), and compared with the flux method and the Bridgman method, mass production is possible at a low process cost.

[0116] Also, through the sintering process, in polycrystalline ceramics, particle growth is maximized to increase the particle size to dozens to hundreds of μm or more (especially when using abnormal grain growth), and the sintered polycrystalline body is crushed to obtain piezoelectric single crystals or aggregates of piezoelectric single crystals with a size of dozens to several bags of μm.

[0117] When manufacturing, sorting, and using piezoelectric single crystals in such a method, the manufacturing cost of the piezoelectric single crystals can be reduced, and mass production of composites can be achieved at a lower process cost.

[0118] In the method for manufacturing a piezoelectric single crystal - polycrystalline ceramic composite of the present invention, the excellent properties of the composite are attributed to the piezoelectric single crystal, but since the polycrystalline ceramic particles also account for 20 to 70% by volume, the selection of the polycrystalline ceramic particles will also be important.

[0119] At this time, the composition of the polycrystalline ceramic particles compounded with the piezoelectric single crystal represented by Chemical Formula 1 is the same as the composition represented by Chemical Formula 1, but can be distinguished from the piezoelectric single crystal by the difference in each composition formula. Also, when the composition of the piezoelectric single crystal and the polycrystalline ceramic particles is different, a synergistic effect can also be expected by the combination of both compositions.

[0120] The above polycrystalline ceramics are not limited to this and may include known polycrystalline compositions.

[0121] At this time, the polycrystalline ceramic particles are required to have (1) high piezoelectric properties, (2) excellent sintering properties due to an increase in density during heat treatment, and (3) high mechanical properties of fracture toughness.

[0122] In the method for manufacturing a piezoelectric single crystal - polycrystalline ceramic composite of the present invention, during the heat treatment process, the perovskite structure ([A][B]O 3Not only the piezoelectric single crystal but also the polycrystalline ceramic particles will have their particle sizes increase simultaneously. Therefore, before the heat treatment, the particle size of the piezoelectric single crystal is preferably 50 μm or more. At this time, if the particle size of the piezoelectric single crystal is less than 50 μm, it will be too small and pulverized, and the effect of composite formation will be extremely small.

[0123] In the case of polycrystalline ceramic particles, the smaller the initial particle size, the more advantageous it is for densification. Therefore, it is selected to be 0.1 μm or more and 0.1 to 5 μm for composite formation.

[0124] Generally, when compared with before the heat treatment, after the heat treatment, the particle size distribution ratio (a / b) will decrease. Therefore, if the particle size distribution ratio (a / b) before the heat treatment is not mixed at 20 or more, the particle size distribution ratio (a / b) after the heat treatment cannot meet the requirement of 20 to 100.

[0125] During the heat treatment, heat treatment is performed so that the particle size of the piezoelectric single crystal grown by particle growth becomes 100 μm or more, and the particle size distribution ratio (a / b) between the piezoelectric single crystal particles (a) and the polycrystalline powder particles (b) after the heat treatment is set to be 20 to 100.

[0126] Also, during the heat treatment, the growth of the single crystal particles consumes the polycrystalline ceramic particles, that is, the single crystal grows while the polycrystalline ceramic particles are contained in the single crystal particles. Therefore, during the heat treatment, due to the growth of the single crystal particles, the single crystal volume ratio also increases.

[0127] Therefore, it is preferable to set the initial input ratio of the piezoelectric single crystal before the heat treatment to 80% by volume or less, and optimize it to be 30 to 80% by volume after the heat treatment.

[0128] When the piezoelectric single crystal and the polycrystalline ceramic particles are mixed and heat-treated, during the heat treatment, both the single crystal and the polycrystalline ceramic particles grow, and the particle size increases. The degree of growth may vary depending on the heat treatment conditions, and thus the physical properties after the heat treatment can be controlled.

[0129] At this time, in the heat treatment conditions, the heat treatment temperature and time are the most important variables, and additional variables such as the heat treatment atmosphere (e.g., oxygen partial pressure), heating rate, and pressure are applied.

[0130] Therefore, depending on the heat treatment conditions, the particle growth rate and density change, so the piezoelectric and mechanical properties are different.

[0131] However, depending on the composition of the piezoelectric single crystal and the ceramics, the optimal heat treatment conditions may change. Preferably, the heat treatment temperature and time are carried out at 900 to 1,300 °C for 1 to 100 hours.

[0132] Also, the heat treatment is preferably carried out at a heating rate of 1 to 20 °C / min. During the heat treatment, the pressure is carried out at 1 to 50 MPa, but it is not limited thereto.

[0133] Furthermore, the present invention obtains a piezoelectric single crystal - polycrystalline ceramic composite by mixing and heat treating a perovskite-type piezoelectric single crystal having the composition formula of Chemical Formula 1 and polycrystalline ceramic particles at a specific particle size distribution ratio.

[0134] The obtained piezoelectric single crystal - polycrystalline ceramic composite maintains the high piezoelectric charge constant and low dielectric loss of the piezoelectric single crystal, and at room temperature, the ratio of the piezoelectric charge constant (Piezoelectric Charge Constant [d 33 (pC / N)]) and the dielectric loss (Dielectric Loss [tanδ(%)]) [= d 33 / tanδ] satisfies 1,000 or more.

[0135] Also, the piezoelectric single crystal - polycrystalline ceramic composite obtained in the present invention maintains the high piezoelectric charge constant and low dielectric loss of the piezoelectric single crystal, while the dielectric constant does not increase significantly. At room temperature, the piezoelectric charge constant (Piezoelectric Charge Constant, d 33 , pC / N]), piezoelectric voltage constant (Piezoelectric Voltage ConsTant, g 33, ×10 -3 The ratio of [=(d 33 ×g 33 ) / tanδ] of the dielectric constant (Dielectric Loss [tanδ (%)]) is 25,000 or more.

[0136] In addition, the piezoelectric single crystal - polycrystalline ceramic composite obtained in the present invention satisfies: (1) The dielectric constant at 30 °C is 3,000 or more, (2) The piezoelectric charge constant (Piezoelectric Charge Constant [d 33 ) is 1,200 pC / N or more, and (3) The phase transition temperature first shown at 30 °C or higher is 80 °C or higher.

[0137] Furthermore, the present invention provides dielectric and piezoelectric application components including a piezoelectric single crystal - polycrystalline ceramic composite having a high dielectric constant (K 3 T ≥ 3,000), a piezoelectric charge constant (d 33 ≥ 1,200 pC / N), an anti - electric field (E C ≥ 3 - 4 kV / cm), and a high internal electric field (E I ≥ 0.5 - 1.0 kV / cm) at the same time.

[0138] Specifically, the piezoelectric application components include ultrasonic transducers (medical ultrasonic diagnostic devices, sonar transducers, non - destructive inspection transducers, ultrasonic cleaners, ultrasonic motors, etc.), piezoelectric actuators (d 33 type actuators, d 31 type actuators, d 15 type actuators, piezoelectric actuators for fine position control, piezoelectric pumps, piezoelectric valves, piezoelectric speakers, bimorph type actuators, and laminated type actuators, etc.), piezoelectric sensors (piezoelectric accelerometers, etc.), and piezoelectric polymer composites (composites of piezoelectric single crystal - polycrystalline ceramic composites and polymers, etc.).

[0139] In addition, examples of the dielectric application components include high-efficiency capacitors, infrared sensors, dielectric filters, field emission transducers, and field-vibration emission transducers.

[0140] <Example> Hereinafter, the present invention will be described in more detail with reference to examples.

[0141] This example is for further specifically explaining the present invention, and the scope of the present invention is not limited to these examples.

[0142] <Example 1> Fabrication and Characterization of a Piezoelectric Single Crystal - Polycrystalline Ceramic Composite 1 By the solid-phase single crystal growth method, a piezoelectric single crystal with the composition of [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3 was manufactured. Also, in the powder synthesis process, excess MgO was added so that the interior of the manufactured single crystal contained 2 vol% of MgO second phase and pore-strengthening phase. As a result of evaluating the piezoelectric charge constant, dielectric constant, and dielectric loss characteristics of the manufactured (001) piezoelectric single crystal, the piezoelectric charge constant (d 33 ) was 2,650 [pC / N], the dielectric constant was 8,773, and the dielectric loss (tanδ) was 0.5%.

[0143] The manufactured [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3After cutting the as-grown piezoelectric single crystal into small pieces, it was continuously pulverized by a ball milling process. The finally pulverized piezoelectric single crystal particles were sorted by size through a sieving process. By adjusting the ball milling process conditions, time, and sieving conditions, piezoelectric single crystal particles with sizes ranging from several tens of micrometers to several millimeters were produced.

[0144] The manufactured piezoelectric single crystal particles were mixed with calcined ceramic powder having a particle size of ~1 μm, formed, and sintered to finally produce a piezoelectric single crystal - polycrystalline ceramic composite. In the mixing step of the piezoelectric single crystal particles and the calcined ceramic powder, the volume of the piezoelectric single crystal was adjusted to produce single crystal - polycrystalline ceramic composites having various volume fractions as shown in Figure 2.

[0145] <Example 2> Fabrication and Characterization of Piezoelectric Single Crystal - Polycrystalline Ceramic Composites 1 By the solid-phase single crystal growth method, a piezoelectric single crystal with the composition of [Pb 0.965 Sr 0.02 Sm 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.25 (Ni 1 / 3 Nb 2 / 3 ) 0.10 Zr 0.30 Ti 0.35 O 3 was manufactured. Also, during single crystal growth, pores in the polycrystalline matrix were trapped inside the single crystal, and the manufactured single crystal contained a pore strengthening phase of about 1.5 vol%. The piezoelectric charge constant (d 33 ) of the manufactured piezoelectric single crystal was 4,457 [pC / N], the dielectric constant was 14,678, and the dielectric loss (Tanδ) was 1.0%.

[0146] The manufactured [Pb 0.965 Sr 0.02 Sm 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.25 (Ni 1 / 3 Nb 2 / 3 ) 0.10Zr 0.30 Ti 0.35 O 3 Except for using the piezoelectric single crystal of the composition, the piezoelectric single crystal particles and the piezoelectric single crystal - polycrystalline ceramic composite were produced by the same process as in Example 1 above.

[0147] The produced piezoelectric single crystal - polycrystalline ceramic composite was adjusted so that the Zr content was lower in the polycrystalline ceramic than in the piezoelectric single crystal. At this time, when the Zr content is low, the sintering temperature of the polycrystalline ceramic can be lowered, and the piezoelectric single crystal can be heat - treated at a lower temperature to minimize the chemical reaction between the piezoelectric single crystal and the polycrystalline ceramic particles, and it has the advantage of minimizing thermal shock and the like generated during the heat - treatment process.

[0148] <Experimental Example 1> Evaluation 1 of Dielectric and Piezoelectric Properties Among the piezoelectric single crystal - polycrystalline ceramic composites produced in Example 1 above, in the composite in which piezoelectric single crystals with an average particle size of ~300 μm and polycrystalline particles with an average particle size of ~10 μm were mixed, formed, and sintered, the piezoelectric charge constant [d 33 (pC / N)], piezoelectric voltage constant [g 33 (mVm / V)], and change in dielectric loss [tanδ (%)] were measured and listed in Table 1 below.

[0149]

Table 1

[0150] Among the single - crystal - polycrystalline ceramic composites in Table 1 above, for the composite produced by mixing with polycrystalline particles with an average particle size of ~10 μm and a volume fraction of piezoelectric single crystals of 70%, the piezoelectric charge constant [d 33 (pC / N)], piezoelectric voltage constant [g 33 (mVm / V)], and change in dielectric loss [tanδ (%)] were measured and listed in Table 2 below.

[0151]

Table 2

[0152] From the above results, [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3 The piezoelectric single crystal - polycrystalline ceramic composite fabricated using the piezoelectric single crystal with the above composition exhibited a higher piezoelectric charge constant (d 33 ), a higher piezoelectric voltage constant (g 33 ) and a lower dielectric loss (Tanδ) compared with existing piezoelectric polycrystalline ceramics. In particular, when the piezoelectric single crystal particle size, volume fraction, and the size ratio of single crystal / polycrystal were specified, the piezoelectric properties of the composite were maximized (d 33 >1,000, d 33 / tanδ>1,000, (d 33 ×g 33 ) / tanδ>30,000).

[0153] Also, when the volume ratio of the piezoelectric single crystal was small, less than 30%, or exceeded 80%, improved piezoelectric and mechanical properties could not be obtained for the polycrystal.

[0154] In particular, when the volume fraction of the single crystal exceeded 80%, the sintering density of the composite was low, it was easily broken during machining, and it was impossible to make a measurement specimen, or it was energized during poling, or the piezoelectric properties tended to decrease rapidly.

[0155] <Experimental Example 2> Evaluation of Dielectric and Piezoelectric Properties 2 After applying silver paste electrodes on both sides of the piezoelectric single crystal - polycrystalline ceramic composite fabricated in the above Example 2 and poling, the evaluation of dielectric and piezoelectric properties was carried out.

[0156] Among the fabricated piezoelectric single crystal - polycrystalline ceramics composites, in the composite where piezoelectric single crystals with an average particle size of ~600 μm and polycrystalline particles with an average particle size of ~8 μm are mixed, formed, and sintered, the piezoelectric charge constant [d 33 (pC / N)], piezoelectric voltage constant [g 33 (mVm / V)], and dielectric loss [tanδ(%)] were measured and are listed in Table 3 below.

[0157]

Table 3

[0158] Among the single crystal - polycrystalline ceramics composites in Table 3 above, for the composite fabricated by mixing with polycrystalline particles with an average particle size of ~8 μm and having a volume fraction of piezoelectric single crystals of 60%, the piezoelectric charge constant [d 33 (pC / N)], piezoelectric voltage constant [g 33 (mVm / V)], and dielectric loss [Tanδ(%)] were measured and are listed in Table 4 below.

[0159]

Table 4

[0160] From the above results, the piezoelectric single crystal - polycrystalline ceramics composite fabricated using the piezoelectric single crystal with the composition of [Pb 0.965 Sr 0.02 Sm 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.25 (Ni 1 / 3 Nb 2 / 3 ) 0.10 Zr 0.30 Ti 0.35 O 3 shows a higher piezoelectric charge constant (d 33 ), higher piezoelectric voltage constant (g 33 ) and dielectric loss (Tanδ) compared with existing piezoelectric polycrystalline ceramics.

[0161] In particular, when the particle size, volume fraction, and single crystal / polycrystal size ratio of the piezoelectric single crystal particles are specified, the piezoelectric properties of the composite are maximized (d 33 > 1,000, d 33 / tanδ > 1,000, (d 33 ×g 33 ) / tanδ > 30,000). If the volume ratio of the piezoelectric single crystal is too small (less than 30%) or extremely large (more than 80%), improved piezoelectric and mechanical properties cannot be obtained for the polycrystal. In particular, when the volume fraction of the single crystal exceeds 80%, the sintering density of the composite is low, it is easily broken during machining, it is impossible to make a measurement specimen, or it is energized during poling, and a tendency for the piezoelectric properties to rapidly decrease is confirmed.

[0162] <Experimental Example 3> Observation of the Change in Dielectric Properties with Temperature and Phase Transition Phenomenon By the solid-phase single crystal growth method, PMN-PT and [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3 composite piezoelectric single crystals were each manufactured. Also, the piezoelectric single crystal-polycrystalline ceramic composite manufactured in Example 1 above was selected as a sample, and the change in dielectric properties with temperature and phase transition phenomenon were observed for the piezoelectric single crystal and the piezoelectric single crystal-polycrystalline ceramic composite.

[0163] Figure 5 shows the results of observing the change in dielectric properties with temperature and phase transition phenomenon of a PMN-PT piezoelectric single crystal manufactured by the solid-phase single crystal growth method. The dielectric constant of the PMN-PT single crystal is higher at the Curie temperature (T C ) than at the phase transition temperature (T RT ) between ferroelectric phases.

[0164] Figure 6 shows [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 )0.4 Zr 0.25 Ti 0.35 O 3 Results of changes in dielectric properties and phase transition phenomena due to temperature for the piezoelectric single crystal of, particularly, at the Curie temperature (T C ), and the dielectric constant was confirmed to be even higher at the phase transition temperature (T RT ) between ferroelectric phases.

[0165] FIG. 7 shows the case of a piezoelectric single crystal - polycrystalline ceramic composite manufactured in Example 1 using the piezoelectric single crystal of [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3 For the dielectric constant at room temperature, the dielectric constant was significantly higher at the phase transition temperature [dielectric constant (@T RT ) > 3 × dielectric constant (@30 °C)], and it was confirmed that the room temperature characteristics of the piezoelectric single crystal - polycrystalline ceramic composite were significantly improved compared to using a general PMN - PT single crystal.

[0166] From the above results, similar to the piezoelectric single crystal, the piezoelectric single crystal - polycrystalline ceramic composite shows a phase transition between ferroelectric phases (such as rhombohedral phase and tetragonal phase) below the Curie temperature (T C ), and the dielectric constant (K 3 T ) was confirmed to be more than three times higher at the phase transition temperature between ferroelectric phases than at room temperature.

[0167] Therefore, more preferably, using a piezoelectric single crystal with a high dielectric constant at the phase transition temperature between ferroelectric phases is effective in improving the piezoelectric properties of the piezoelectric single crystal - polycrystalline ceramic composite.

[0168] <Experimental Example 4> Evaluation of Mechanical Properties For [Pb 0.965 Sr 0.02 La 0.01 [(Mg1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3 Using the piezoelectric single crystal of the composition as a sample, the piezoelectric single crystal - polycrystalline ceramic composite of Example 1 manufactured thereby, mechanical properties such as fracture strength and fracture toughness were comparatively evaluated. At this time, the fracture strength value was measured by the four - point bending strength measurement method according to the ASTM method.

[0169] Among the piezoelectric single crystal - polycrystalline ceramic composites of Example 1 presented in Table 1 above, both composites with volume fractions of 40% and 60% were selected as specimens, and the fracture strength was compared with that of the (001) piezoelectric single crystal specimen. The results are shown in Table 5 below.

[0170]

Table 5

[0171] Also, among the piezoelectric single crystal - polycrystalline ceramic composites of Example 1 presented in Table 1 in Table 2 above, specimens of both composites with single crystal sizes of 200 μm and 500 μm were selected, and the fracture strength was compared with that of the (001) piezoelectric single crystal specimen. The results are shown in Table 6 below.

[0172]

Table 6

[0173] From the above results, compared with the piezoelectric single crystal of [Pb 0.965 Sr 0.02 La 0.01 [(Mg 1 / 3 Nb 2 / 3 ) 0.4 Zr 0.25 Ti 0.35 O 3 the piezoelectric single crystal - polycrystalline ceramic composite shows fracture strength and fracture toughness values more than twice as high, and this value was confirmed to be similar to that of general piezoelectric polycrystalline ceramics.

[0174] Therefore, it was confirmed that the fracture strength and fracture toughness of the piezoelectric single crystal-polycrystalline ceramics composite manufactured in this experimental example increased by about two times compared with those of the piezoelectric single crystal.

[0175] In addition, in the piezoelectric single crystal-polycrystalline ceramics composite, the matrix of the polycrystals surrounding the single crystal not only has higher mechanical properties than the single crystal itself, but also plays a role in protecting the single crystal from external mechanical impacts, resulting in a significant improvement in the mechanical performance of the composite.

[0176] By combining the single crystal with excellent piezoelectric properties and the polycrystalline ceramics with excellent mechanical properties as described above, a composite excellent in all of both properties was fabricated, which maintained the high piezoelectric properties of the piezoelectric single crystal and improved the mechanical brittleness characteristics.

[0177] As described above, the present invention has been described in detail only for the described specific examples, but it is obvious to those skilled in the art that various modifications and corrections are possible within the scope of the technical idea of the present invention, and these modifications and corrections belong to the appended claims.

Claims

1. A perovskite-type structure containing lead zirconate ([A][B]O ３ ) is a piezoelectric single crystal-polycrystalline ceramic composite in which a piezoelectric single crystal of the above formula (1) is composited with polycrystalline ceramic particles, The average particle size (a) of the piezoelectric single crystal is 200 to 1,000 μm; The average particle size (b) of the polycrystalline ceramic particles is 2 to 20 μm; a ratio (a / b) of the average grain size (a) of the piezoelectric single crystal to the average grain size (b) of the polycrystalline ceramic grains is 20 to 100; The piezoelectric charge constant (d) of the piezoelectric single crystal-polycrystalline ceramic composite at room temperature ３３ , pC / N) and the ratio of dielectric loss (tan δ (%)) [d ３３ / tan δ] is 1,000 or more.

2. A piezoelectric single crystal-polycrystal ceramic composite comprising:

2. The piezoelectric single crystal is contained in an amount of 30 to 80% by volume.

2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

3. In the composite, the piezoelectric single crystal is oriented in the crystal direction of <001> or <011>.

2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

4. The piezoelectric single crystal-polycrystalline ceramic composite is, at room temperature, (1) Dielectric constant (K ３ Ｔ ) more than 3,000, (2) Piezoelectric Charge Constant (d ３３ ) is 1,200 pC / N or more, and (3) The first phase transition temperature is 80° C. or higher.

2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

5. The piezoelectric single crystal-polycrystalline ceramic composite has a Curie temperature (T Ｃ ) or less, a phase transition between ferroelectric phases occurs, and the dielectric constant (K ３ Ｔ ) is more than three times higher at the phase transition temperature between ferroelectric phases than at room temperature.

2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

6. The piezoelectric single crystal-polycrystalline ceramic composite has a piezoelectric charge constant (d ３３ , pC / N), Piezoelectric Voltage Constant (Piezoelectric Voltage Constant, g ３３ , 10 －３ Vm / N)) and the dielectric loss (Tan δ%) [(d ３３ ×g ３３ ) / tan δ] is 25,000 or more 2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

7. The piezoelectric single crystal-polycrystalline ceramic composite has a part or all of the empty space inside the composite filled with a polymer.

2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

8. The Zr content in the piezoelectric single crystal is higher than that in the polycrystalline ceramic particles.

2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

9. The piezoelectric single crystal has the following chemical formula 1: Chemical formula 1 [A １－（ａ＋１．５ｂ） B ａ C ｂ ][(MN) １－ｘ－ｙ (L) ｙ Ti ｘ ]O ３－ｚ (In the above formula, A is Pb or Ba; B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn, and Sr; C is at least one selected from the group consisting of Co, Fe, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; L is selected from Zr or Hf, either alone or in a mixed form; M is at least one selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb, and Zn; N is at least one selected from the group consisting of Nb, Sb, Ta, and W; 0<a≦0.10, 0<b≦0.05, 0.05≦x≦0.58, 0.05≦y≦0.62, and 0≦z≦0.02). having the formula 2. The piezoelectric single crystal-polycrystal ceramic composite according to claim 1.

10. In the above formula, 0.01≦a≦0.10 and 0.01≦b≦0.

05.

10. The piezoelectric single crystal-polycrystal ceramic composite according to claim 9.

11. In the above formula, a / b≧2.

10. The piezoelectric single crystal-polycrystal ceramic composite according to claim 9.

12. In the above formula, 0.10≦x≦0.58 and 0.10≦y≦0.

62.

10. The piezoelectric single crystal-polycrystal ceramic composite according to claim 9.

13. In the piezoelectric single crystal, when L is a mixed type, it is represented by the following formula 2 or 3: chemical formula 2 [A １－（ａ＋１．５ｂ） B ａ C ｂ ][(MN) １－ｘ－ｙ (Zr) １－ｗ ,Hf ｗ ) ｙ Ti ｘ ]O ３ chemical formula 3 [A １－（ａ＋１．５ｂ） B ａ C ｂ ][(MN) １－ｘ－ｙ (Zr) １－ｗ ,Hf ｗ ) ｙ Ti ｘ ]O ３－ｚ (In the above formula, A, B, C, M, N, a, b, x, y, and z are the same as those in Chemical Formula 1, with the proviso that 0.01≦w≦0.20.) having the formula 10. The piezoelectric single crystal-polycrystal ceramic composite according to claim 9.

14. The composition of the piezoelectric single crystal further includes a reinforcing second phase (P) of 0.1 to 20% by volume.

10. The piezoelectric single crystal-polycrystal ceramic composite according to claim 9.

15. The reinforcing second phase P is a metal phase, an oxide phase, or a pore. The piezoelectric single crystal-polycrystal ceramic composite according to claim 14.

16. The strengthening second phase P is Au, Ag, Ir, Pt, Pd, Rh, MgO, ZrO ２ and pores.

16. The piezoelectric single crystal-polycrystal ceramic composite according to claim 15.

17. The reinforcing second phase P is distributed uniformly in the form of particles in the piezoelectric single crystal, or is regularly distributed in a certain pattern. The piezoelectric single crystal-polycrystal ceramic composite according to claim 16.

18. By solid-phase single crystal growth, a perovskite-type structure containing lead zirconate ([A][B]O ３ ) a piezoelectric single crystal, and then the piezoelectric single crystal is crushed to a size of 50 μm or more to prepare single crystal particles (a); preparing polycrystalline powder particles (b) having an average particle size of 0.1 to 5 μm, mixing the particles so that the ratio a / b of the average particle size (a) of the piezoelectric single crystal before heat treatment to the average particle size (b) of the polycrystalline ceramic particles is 20 or more, and then heat treating the mixture; The heat treatment is performed to grow the piezoelectric single crystal to a grain size of 100 μm or more, and after the heat treatment, the ratio a / b is set to 20 to 100. The present invention relates to a method for producing a piezoelectric single crystal-polycrystal ceramic composite.

19. During the mixing, the piezoelectric single crystal was contained in an amount of 80% by volume or less. The method for producing a piezoelectric single crystal-polycrystal ceramic composite according to claim 18.

20. After the heat treatment, the piezoelectric single crystal was contained in an amount of 30 to 80% by volume. The method for producing a piezoelectric single crystal-polycrystal ceramic composite according to claim 18.

21. After the heat treatment, the average particle size distribution (a) of the grown piezoelectric single crystal is 100 to 1,000 μm, the average particle size distribution (b) of the grown polycrystalline grain is 2 to 20 μm, and the particle size distribution a / b is 20 to 100. The method for producing a piezoelectric single crystal-polycrystal ceramic composite according to claim 18.

22. The heat treatment was carried out at 900 to 1,300° C. for 1 to 100 hours. The method for producing a piezoelectric single crystal-polycrystal ceramic composite according to claim 18.

23. The heat treatment was carried out at a heating rate of 1 to 20° C. / min. The method for producing a piezoelectric single crystal-polycrystal ceramic composite according to claim 18.

24. A piezoelectric ceramic material comprising the piezoelectric single crystal-polycrystal ceramic composite according to any one of claims 1 to 17. A piezoelectric application component and a dielectric application component characterized by the above.

25. The piezoelectric application part and the dielectric application part are any one selected from the group consisting of ultrasonic transducers, piezoelectric actuators, piezoelectric sensors, dielectric capacitors, electric field generating transducers, and electric field and vibration generating transducers.

25. The piezoelectric and dielectric application components according to claim 24.

Images