Ferroelectric piezoelectric single crystal having spontaneous poling characteristic, method for manufacturing same, and piezoelectric and dielectric application parts using same

Abstract

The present invention relates to a ferroelectric piezoelectric single crystal having a spontaneous poling characteristic, a method for manufacturing same, and piezoelectric and dielectric application parts using same. The ferroelectric piezoelectric single crystal of the present invention can realize high piezoelectric properties itself without poling treatment by an external electric field, by greatly increasing the effect of electrical defects under the conditions of a specific secondary phase inside the single crystal through a change in the composition of [A] site ions, [B] site ions, and [C] site ions, in a perovskite-type crystal structure ([A][B]O3), and changes in the volume fraction and average size [D50] of a secondary phase. Furthermore, by maintaining high piezoelectric characteristics while having thermal and electrical stability in a wide temperature range, piezoelectric application parts and dielectric application parts, using same, can be stably used without degradation in characteristics under a wide range of usage conditions such as temperature, electric field, and pressure.

Description

Ferroelectric piezoelectric single crystal with spontaneous poling properties, its manufacturing method, and piezoelectric and dielectric application components using the same

[0001] The present invention relates to a ferroelectric piezoelectric single crystal having spontaneous poling characteristics, a method for manufacturing the same, and piezoelectric and dielectric application components using the same, and more particularly, to a perovskite crystal structure ([A][B]O3), a compositional change of [A] site ions, [B] site ions, and [O] site ions, and a volume fraction and average size of a secondary phase [D 50 ] through changes, the secondary phase and electrical defects coexist inside the ferroelectric piezoelectric single crystal, and the effect of electrical defects is greatly increased under specific secondary phase conditions inside the single crystal, thereby increasing the piezoelectric constant (d) without poling treatment by an external electric field. 33 ) relates to a ferroelectric piezoelectric single crystal having spontaneous poling characteristics that realize high piezoelectric properties satisfying 500 to 5,000 pC / N, a method for manufacturing the same, and piezoelectric and dielectric application components using the same.

[0002] Ferroelectric piezoelectric single crystals with perovskite crystal structure ([A][B]O3) have a significantly higher dielectric constant (K3) than conventional piezoelectric polycrystalline materials. T ) and piezoelectric constant (d 33 and k 33 ) and is used in high-performance components such as piezoelectric actuators, ultrasonic transducers, piezoelectric sensors, and dielectric capacitors, and its application as a substrate material for various thin film devices is also expected.

[0003] Among the piezoelectric single crystals with perovskite crystal structure developed to date, PMN-PT (Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3), PZN-PT (Pb(Zn 1 / 3 Nb 2 / 3 )O3-PbTiO3), PInN-PT (Pb(In 1 / 2 Nb 1 / 2)O3-PbTiO3), PYbN-PT (Pb(Yb 1 / 2 Nb 1 / 2 )O3-PbTiO3), PSN-PT (Pb(Sc 1 / 2 Nb 1 / 2 )O3-PbTiO3), PMN-PInN-PT, PMN-PYbN-PT, and BiScO3-PbTiO3(BS-PT). These single crystals exhibit eutectic melting behavior when melted, and have been conventionally manufactured using conventional single crystal growth methods such as the flux method and Bridgman method.

[0004] However, the previously developed piezoelectric single crystals of PMN-PT and PZN-PT have high dielectric and piezoelectric properties (K3) at room temperature. T >4,000, d 33 >1,400 pC / N, k 33 >0.85), but has the advantage of low phase transition temperatures (T C Wow T RT ), low coercive electric field (E C ) and brittleness, the usage conditions (temperature, electric field, pressure, etc.) of piezoelectric single crystals are significantly limited.

[0005] In general, it is known that piezoelectric single crystals with a perovskite crystal structure have the highest dielectric and piezoelectric properties in the region near the MPB (morphotropic phase boundary), that is, the phase boundary between the rhombohedral and tetragonal phases.

[0006] However, since piezoelectric single crystals with a perovskite crystal structure generally show the best dielectric and piezoelectric properties when in the rhombohedral phase, the rhombohedral piezoelectric single crystals are most actively applied. However, the rhombohedral piezoelectric single crystals have a phase transition temperature (T) between the rhombohedral phase and the tetragonal phase. RT ) is stable only below the maximum temperature at which the rhombohedral phase can be stable, T RTIt can only be used below. Therefore, T RT When the phase transition temperature is low, the use temperature of the rhombohedral piezoelectric single crystal is lowered, and the manufacturing temperature and use temperature of the piezoelectric single crystal application parts are also T RT Limited to the following.

[0007] Also, the phase transition temperatures (T C Wow T RT ) and the anti-electromagnetic field (E C ) are low, piezoelectric single crystals are easily depoled and lose their excellent dielectric and piezoelectric properties under mechanical processing, stress, heat generation and driving voltage. Therefore, the phase transition temperatures (T C Wow T RT ) and the anti-electromagnetic field (E C ) have limitations in the conditions for manufacturing single crystal application parts, operating temperature conditions, and driving voltage conditions. In the case of PMN-PT single crystals, T is generally C <150℃, T RT <80℃ and E C <2.5 kV / cm, and for PZN-PT single crystals, T is typically C <170℃, T RT <100℃ and E C <3.5 kV / cm. In addition, the development and commercialization of piezoelectric single crystal application components have been hindered due to limitations in manufacturing conditions, operating temperature range, and operating voltage conditions of dielectric and piezoelectric single crystal application components.

[0008] To overcome the shortcomings of piezoelectric single crystals, new compositions of single crystals, 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, are also being studied.

[0009] However, in the case of these single crystals, the dielectric constant, piezoelectric constant, phase transition temperature, coercive field and mechanical properties could not be improved simultaneously, and piezoelectric single crystals mainly composed of expensive elements such as Sc and In have a problem that hinders the practical use of single crystals due to the high single crystal manufacturing cost.

[0010] There are three main reasons why piezoelectric single crystals with a perovskite crystal structure, including PMN-PT, developed to date show low phase transition temperatures. First, the phase transition temperature of the relaxor (PMN or PZN, etc.), which is the main component along with PT, is low.

[0011] Second, because the MPB, which forms the boundary between the tetragonal and rhombohedral phases, is not perpendicular to the temperature axis but is gently tilted, the phase transition temperature (T) between the rhombohedral and tetragonal phases is RT ) to raise the Curie temperature (T C ) is inevitable, so the Curie temperature (T C ) and the phase transition temperature (T) between the rhombohedral and tetragonal phases RT ) is difficult to raise at the same time.

[0012] Third, even when a relaxer with a relatively high phase transition temperature (such as PYbN, PInN, or BiScO3) is mixed with PMN-PT, the phase transition temperature does not simply increase in proportion to the composition, or the dielectric and piezoelectric properties deteriorate.

[0013] Furthermore, the Relaxor-PT single crystals presented in non-patent literature 1 are mainly manufactured using existing single crystal growth methods such as the flux method and the Bridgman method that utilize melting processes. However, due to the single crystal manufacturing process, it is difficult to manufacture large single crystals with uniform composition, and the manufacturing cost is high, making mass production difficult, so commercialization has not yet been successful.

[0014] Additionally, compared to piezoelectric polycrystalline ceramics in general, piezoelectric single crystals have a higher piezoelectric constant (d33 ≥2,000∼4,000 pC / N), but because the coercive electric field is low (EC≤2 kV / cm), it is easily depoled, so its electrical stability is low and its practical use is limited. Therefore, the coercive electric field (E) of the piezoelectric single crystal C ) and internal electric field (Internal Bias Electric Field, E I ) has been proposed, but the increase in the resistive field and internal electric field is accompanied by a decrease in piezoelectric properties, so its low effectiveness has been pointed out.

[0015] In particular, the piezoelectric properties of ferroelectric materials are maximized when the material is poled under high electric fields at low temperatures. However, as the temperature increases, the aligned electric domains in the low-temperature poling shift into disorder, causing depolarization. This weakens or even disappears the piezoelectric properties of ferroelectric materials at temperatures well below the Curie temperature, making their practical operating temperatures much lower.

[0016] Therefore, significant piezoelectric response in ferroelectrics occurs only after poling by an external electric field applied along a specific crystal structure, and the piezoelectric effect disappears upon heating above the Curie temperature (Tc), thus eliminating the poled state. This thermally induced depoling limits the temperature range of applications in piezoelectric devices.

[0017] Accordingly, the inventors of the present invention have designed a method to maintain high piezoelectric properties and electrical and temperature stability of a ferroelectric piezoelectric single crystal by appropriately increasing the types and concentrations of structural and electrical defects inside the ferroelectric piezoelectric single crystal to improve the problems of the prior art, and in a perovskite crystal structure ([A][B]O3), the compositional changes of [A] site ions, [B] site ions, and [O] site ions and the volume fraction and average size of the secondary phase [D 50] By controlling the type, size and fraction of the secondary phase inside the single crystal and the type and concentration of various lattice defects (Point Defects) and lattice defect associations (Defect Associates such as Defect Dipoles), the present invention was completed by confirming the properties that simultaneously satisfy the high piezoelectric constant characteristic of the single crystal while having the spontaneous poling characteristic essential for the thermal and electrical stability of the single crystal without significantly increasing the coercive field and internal electric field of the ferroelectric piezoelectric single crystal.

[0018] (Patent Document 1) Republic of Korea Patent No. 0564092 (announced on March 27, 2006)

[0019] (Patent Document 2) Republic of Korea Patent No. 0743614 (Published on July 30, 2007)

[0020] (Non-patent Document 1) IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 44, no. 5, 1997, pp. 1140-1147.

[0021] The purpose of the present invention is to provide a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having spontaneous poling characteristics.

[0022] Another object of the present invention is to provide a method for manufacturing the ferroelectric piezoelectric single crystal.

[0023] Another object of the present invention is to apply the ferroelectric piezoelectric single crystal and a composite including the same to a piezoelectric component or a dielectric component.

[0024] In order to achieve the above-mentioned purpose, the present invention provides a piezoelectric charge constant (d) of a single crystal. 33 ) is 500 to 5,000 pC / N, and the internal bias electric field (Internal Bias Electric Field, E) of the single crystal I) provides a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having a piezoelectric property of 1.0 kV / cm or less and a secondary phase mixed in at 2 to 12 volume% inside the single crystal, thereby having spontaneous poling characteristics.

[0025] Among the above piezoelectric properties, the internal bias electric field (E) is more preferable. I ) 0.5 kV / cm or less, and the hydrostatic piezoelectric constant (d h ) meets 200 to 1,500 pC / N.

[0026] The ferroelectric piezoelectric single crystal of the above perovskite type crystal structure ([A][B]O3) has a Curie temperature (T C ) or maximum dielectric constant temperature (T MAX ) and room temperature (20°C), and the piezoelectric constant of the single crystal is maintained in the temperature range of 10 to 250°C due to the spontaneous poling characteristic.

[0027] In the ferroelectric piezoelectric single crystal of the present invention, two or more secondary phases selected from a metal phase, an oxide phase, or a pore are mixed, and at this time, the average size of the secondary phase [D 50 ] is preferably 2 to 20㎛.

[0028] Additionally, it is desirable that the pores be at least 50% by volume compared to the total volume occupied by the secondary phase within the piezoelectric single crystal.

[0029] The present invention is a method for manufacturing the above piezoelectric single crystal,

[0030] (a) a step of reducing the number density (number of abnormal grains / unit area) of abnormal grains by controlling the average size of matrix grains of a polycrystal having a piezoelectric single crystal composition of a perovskite type crystal structure ([A][B]O3); and

[0031] (b) A method for manufacturing a piezoelectric single crystal is provided, comprising: a step of heat-treating a polycrystal having a reduced number density of abnormal particles obtained through the above step (a) to grow abnormal particles; wherein a powder having a composition of [A] site ions and [B] site ions constituting the piezoelectric single crystal is calcined at a temperature of 600 to less than 1,000°C to obtain a powder molded body; a first heat treatment process for sintering the powder molded body and a second heat treatment process during the single crystal growth are performed; and a secondary phase is controlled to be included in the powder molded body at a volume fraction of 2 to 12% by volume.

[0032] In addition, the average size of the above secondary phase [D 50 ] is preferably adjusted to 2 to 20㎛.

[0033] The above method for manufacturing a piezoelectric single crystal controls the composition of [A] site ions and [B] site ions in a piezoelectric single crystal having a perovskite crystal structure ([A][B]O3), and controls the oxygen partial pressure during heat treatment in the manufacturing process, thereby allowing electrical defects and secondary phases to coexist inside the single crystal, and significantly increases the effect of electrical defects under specific secondary phase conditions inside the single crystal, thereby maintaining the high dielectric constant and piezoelectric constant inherent in the piezoelectric single crystal without poling treatment by an external electric field. Therefore, the present invention can sufficiently induce spontaneous poling characteristics that are not observed in general PMN-PT single crystals, thereby providing a piezoelectric single crystal with high resistance to external environments.

[0034] Furthermore, the present invention provides piezoelectric application components and dielectric application components using a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having the above-described spontaneous poling characteristics.

[0035] In addition, the present invention provides a ferroelectric piezoelectric single crystal having a perovskite crystal structure ([A][B]O3) having the above-described spontaneous poling characteristics, a piezoelectric single crystal composite in which the single crystal and a polymer are mixed, and a piezoelectric application component and a dielectric application component using the piezoelectric single crystal composite are provided.

[0036] Examples of the above piezoelectric application components and dielectric application components may 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.

[0037] The ferroelectric piezoelectric single crystal according to the present invention has a piezoelectric constant (d) due to spontaneous poling that is not subjected to poling by an external electric field. 33 ) It has excellent piezoelectric properties of more than 500 pC / N and Curie temperature (T C ) and then cooled to room temperature, the piezoelectric charge constant (d) at room temperature before heat treatment 33 ) Since the characteristics are maintained by more than 80%, it is possible to fundamentally solve the problem of depoling when excessive temperature or pressure is applied during the manufacturing process and use of piezoelectric single crystal application components.

[0038] In addition, it is possible to manufacture piezoelectric single crystals using a solid-state single crystal growth method suitable for mass production of single crystals and to develop a single crystal composition that does not include expensive raw materials, thereby enabling the commercialization of piezoelectric single crystals.

[0039] Furthermore, the present invention can provide a piezoelectric application component and a dielectric application component using a piezoelectric single crystal having a spontaneous poling characteristic that can maintain high piezoelectric properties while maintaining thermal and electrical stability, and the piezoelectric application component and the dielectric application component can be manufactured and used in a wide temperature range, and can be used stably without deterioration of properties under a wide range of usage conditions (temperature, electric field, pressure, etc.).

[0040] Figure 1 is a microstructure photograph (low secondary phase fraction) of a ferroelectric piezoelectric single crystal of a perovskite type crystal structure according to Example 1 of the present invention.

[0041] Figure 2 is a microstructure photograph (high secondary phase fraction) of a ferroelectric piezoelectric single crystal of a perovskite type crystal structure according to Example 1 of the present invention.

[0042] Figure 3 is a photograph of a ferroelectric piezoelectric single crystal with a perovskite crystal structure according to Example 2 of the present invention.

[0043] Figure 4 is a microscopic photograph of a ferroelectric piezoelectric single crystal with a perovskite crystal structure of Figure 3.

[0044] Figure 5 shows the Curie temperature (T) of a ferroelectric piezoelectric single crystal of a perovskite type crystal structure according to Example 1 of the present invention. C ) Repeatedly heat-treated 5 times up to 250℃, and the dielectric constant change curve according to the temperature measured at the 5th time.

[0045] Figure 6 shows the Curie temperature (T) of a ferroelectric piezoelectric single crystal of a perovskite type crystal structure according to Example 2 of the present invention. C ) is a temperature-dependent dielectric constant change curve measured while repeatedly heat-treating 5 times up to 250℃.

[0046] Figure 7 shows the Curie temperature (T) of a typical PMN-PT single crystal according to Comparative Example 1 of the present invention. C ) This is a curve showing the change in dielectric constant according to temperature measured while repeatedly heat-treating 5 times up to 250℃.

[0047] Hereinafter, the present invention will be described in detail.

[0048] The present invention relates to a piezoelectric charge constant (d) of a single crystal. 33 ) is 500 to 5,000 pC / N, the internal bias electric field (E) of a single crystal I ) provides a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having a piezoelectric property of 1.0 kV / cm or less and a secondary phase mixed in at 2 to 12 volume% inside the single crystal, thereby having spontaneous poling characteristics.

[0049] In general, in a perovskite crystal structure, by adding additives such as donors and acceptors, the types and concentrations of various electrical lattice defects (point defects) and lattice defect bonds (defect associates such as defect dipoles) inside the piezoelectric single crystal can be controlled, and the internal electric field inside the single crystal can be controlled.

[0050] Accordingly, the present invention has confirmed that in a perovskite crystal structure ([A][B]O3), the formation of electrical defects and internal electric fields by additives such as donors and acceptors are greatly affected by the type, size, and fraction of secondary phases inside a single crystal, and thus, by controlling the composition change of [A] site ions, [B] site ions, and [O] site ions in the crystal structure and the oxygen partial pressure during heat treatment in the manufacturing process, the type, size, and fraction of secondary phases inside the single crystal and the type and concentration of various lattice defects (Point Defects) and lattice defect bonds (Defect Associates such as Defect Dipoles) are controlled, thereby providing a piezoelectric single crystal that simultaneously satisfies the high piezoelectric constant characteristics of a piezoelectric single crystal while having spontaneous poling characteristics.

[0051] The ferroelectric piezoelectric single crystal of the present invention having a perovskite crystal structure ([A][B]O3) with spontaneous poling properties

[0052] (1) Piezoelectric charge constant (d) of single crystal 33 ) meets 500 to 5,000 pC / N, preferably 500 to 3,000 pC / N, more preferably 1,000 to 5,000 pC / N,

[0053] (2) Internal Bias Electric Field (E) of a single crystal I ) simultaneously satisfies the property of 1.0 kV / cm or less, more preferably 0.5 kV / cm or less,

[0054] (3) When the volume fraction of the secondary phase inside the single crystal is mixed at 2 to 12% by volume, the ferroelectric piezoelectric single crystal exhibits high piezoelectric properties without poling treatment, that is, spontaneous poling properties are induced.

[0055] The ferroelectric piezoelectric single crystal of the above perovskite type crystal structure ([A][B]O3) has a Curie temperature (T C) or maximum dielectric constant temperature (T MAX ) and room temperature (20°C), and the piezoelectric constant of the single crystal is maintained in the temperature range of 10 to 250°C due to the spontaneous poling characteristic.

[0056] In the ferroelectric piezoelectric single crystal of the present invention, two or more secondary phases selected from a metal phase, an oxide phase, or a pore are mixed, and at this time, the average size of the secondary phase [D 50 ] is preferably 2 to 20㎛.

[0057] In addition, the piezoelectric single crystal of the present invention has a hydrostatic piezoelectric constant (d h ) shows a high value of 200 to 1,500 pC / N, and the hydrostatic piezoelectric constant (d h ) is calculated by the following formula.

[0058] d h = d 33 + 2 d 31

[0059] Generally d 33 is positive but d 31 is negative, and d 31 Silver d 33 It is about 50% to 30% of d, resulting in h is very small, less than 100.

[0060] However, the piezoelectric single crystal of the present invention is uniquely d 31 This d 33 It is about 20% to 5% of d 33 is high, ranging from 500 to 5,000 pC / N, resulting in a hydrostatic piezoelectric constant (d h ) provides a ferroelectric piezoelectric single crystal of perovskite type crystal structure ([A][B]O3) satisfying the properties of 200 to 1,500 pC / N.

[0061] The ferroelectric piezoelectric single crystal of the present invention having a perovskite crystal structure ([A][B]O3) with spontaneous poling characteristics induces spontaneous poling characteristics in the piezoelectric single crystal by controlling the type, size and fraction of the secondary phase inside the single crystal and the type and concentration of various lattice defects (point defects) and lattice defect bonds (defect associates such as defect dipoles), thereby maintaining high piezoelectric characteristics of the piezoelectric single crystal and a wide range of use (temperature, electric field, pressure, etc.).

[0062] The above dielectric constant and piezoelectric constant values ​​can be evaluated under the same temperature conditions of room temperature, and in the specification of the present invention, unless otherwise specified, the dielectric constant and piezoelectric constant values ​​evaluated at room temperature (20°C) are referred to.

[0063] The present invention provides a ferroelectric piezoelectric single crystal having a perovskite crystal structure ([A][B]O3) having a composition formula of the following chemical formula 1.

[0064] Chemical Formula 1

[0065] [A 1-(a+1.5b) B a C b ][(MN) 1-x-y (L) y Ti x ]O 3-z

[0066] In the above formula,

[0067] A is Pb or Ba,

[0068] B is at least one selected from the group consisting of Ba, Ca, Co, Fe, Ni, Sn and Sr,

[0069] 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,

[0070] L is a single or mixed form selected from Zr or Hf,

[0071] M is at least one species selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb and Zn,

[0072] N is at least one species selected from the group consisting of Nb, Sb, Ta and W,

[0073] 0 <a≤0.10, 0<b≤0.05, 0.05≤x≤0.58, 0.05≤y≤0.62 및 0≤z≤0.03이다.

[0074] The piezoelectric single crystal having the chemical formula of the present invention has a perovskite crystal structure ([A][B]O3) in which the [A] site ions are formed into a composite composition based on the tendency for the piezoelectric properties to increase as the chemical composition becomes more complex. At this time, if we look specifically at the composite composition of the [A] site ions in the piezoelectric single crystal having the chemical formula of the present invention, [A 1-(a+1.5b) B a C b ], and the above A composition includes a flexible or lead-free element. In the embodiment of the present invention, the description is limited to a flexible piezoelectric single crystal in which A is Pb, but is not limited thereto.

[0075] In the above [A] site ion, the B composition is at least one selected from the group consisting of a divalent metal element, preferably Ba, Ca, Co, Fe, Ni, Sn and Sr, and the C composition is used if it is a trivalent metal element.

[0076] Preferably, at least one element is 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, one or two lanthanide elements are used in a mixed form.

[0077] In the composite composition of the [A] site ion in the piezoelectric single crystal having the composition formula of the above chemical formula 1, [A] corresponding to the [A] site ion1-(a+1.5b) B a C b ] The composition is a requirement for realizing the target properties, and is characterized by being composed by combining a metal divalent element and a metal trivalent element when A is a flexible or lead-free piezoelectric single crystal.

[0078] Preferably, in the composite composition of the [A] site ion corresponding to the donor in the piezoelectric single crystal composition of Chemical Formula 1, 0.01≤a≤0.10 and 0.01≤b≤0.05 should be satisfied, and more preferably, a / b≥2 should be satisfied. At this time, 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, making it difficult to use in practice, which is not preferable.

[0079] In addition, if the requirement of a / b≥2 is not satisfied, it is not desirable because the dielectric and piezoelectric properties are not maximized or single crystal growth is limited.

[0080] At this time, in the composite composition of the [A] site ion in the piezoelectric single crystal having the composition formula of Chemical Formula 1, an excellent dielectric constant can be realized when the composite composition is compared to the case where the composite composition is composed of only a metal trivalent element or a metal divalent element.

[0081] According to the generally known [A][MN]O3-PbTiO3-PbZrO3 phase diagram, the composition region exhibiting excellent dielectric and piezoelectric properties is shown around the phase boundary (MPB) of the rhombohedral and tetragonal phases. In the [A][MN]O3-PbTiO3-PbZrO3 phase diagram, the dielectric and piezoelectric properties are maximized at the phase boundary of the rhombohedral and tetragonal phases, and the dielectric and piezoelectric properties gradually decrease as the composition moves away from the MPB composition. In addition, when the composition changes from the MPB composition to the rhombohedral region within 5 mol%, the dielectric and piezoelectric properties decrease little, maintaining very high dielectric and piezoelectric property values. When the composition changes from the MPB composition to the tetragonal region, the dielectric and piezoelectric properties decrease more rapidly than in the rhombohedral region. However, even when the composition is within 5 mol% or 10 mol% in the tetragonal region, the dielectric and piezoelectric properties continuously decrease, but the dielectric and piezoelectric property values ​​are sufficiently high to be applied to dielectric and piezoelectric application components.

[0082] The phase boundary (MPB) of PbTiO3 and PbZrO3 is known as PbTiO3: PbZrO3= x: y = 0.48: 0.52 (molar ratio).

[0083] When the composition changes from the MPB composition to the rhombohedral and tetragonal regions by 5 mol% each, the maximum values ​​of x and y become 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). And when the composition changes from the MPB composition to the rhombohedral and tetragonal regions by 10 mol% each, the maximum values ​​of x and y become 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 MPB composition, high dielectric and piezoelectric property values ​​were maintained within the range of 5 mol% composition in the rhombohedral and tetragonal regions, respectively, and in the MPB composition, high dielectric and piezoelectric property values ​​were shown sufficiently high for application to dielectric and piezoelectric application components within the range of 10 mol% composition in the rhombohedral and tetragonal regions, respectively.

[0084] In addition, when the content of PbTiO3 and PbZrO3, i.e., the x and y values, are 0.05 or less, the phase boundary between the rhombohedral phase and the tetragonal phase cannot be formed, or the phase transition temperatures and coercive fields are too low, making it unsuitable for the present invention.

[0085] Therefore, in the composite composition of the [B] site ion corresponding to the acceptor in the piezoelectric single crystal composition having the composition formula of the above chemical formula 1, x is preferably in the range of 0.05≤x≤0.58, and more preferably 0.10≤x≤0.58. In this case, when x is less than 0.05, the phase transition temperature (Tc and T RT ), piezoelectric constant (d 33 , k 33 ) or the dielectric constant (K3) is low when the coercive field (Ec) is low and x exceeds 0.58. T ), piezoelectric constant (d 33 , k 33 ) or phase transition temperature (T RT) is low. Meanwhile, y is preferably in the range of 0.05≤y≤0.62, and more preferably satisfies 0.10≤y≤0.62. The reason is that when y is less than 0.05, the phase transition temperature (Tc and T RT ), piezoelectric constant (d 33 , k 33 ) or if the coercive field (Ec) is low and exceeds 0.62, the dielectric constant (K3 T ) or piezoelectric constant (d 33 , k 33 ) is low.

[0086] The piezoelectric single crystal having the composition formula of chemical formula 1 of the present invention has a perovskite crystal structure ([A][B]O3), and includes a metal tetravalent element in the [B] site ion, but is limited to a single or mixed form selected from Zr or Hf, particularly for the L composition.

[0087] In the above mixed form, a piezoelectric single crystal having a composition formula of the following chemical formula 2 is provided.

[0088] Chemical Formula 2

[0089] [A 1-(a+1.5b) B a C b ][(MN) 1-x-y (Zr 1-w , Hf w ) y Ti x ]O 3-z

[0090] In the above, A, B, C, M and N are the same as in the chemical formula 1, and a, b, x and y are also the same, except that 0.01≤ w≤0.20.

[0091] At this time, if the above w is less than 0.01, there is a problem that the dielectric and piezoelectric properties are not maximized, and if it exceeds 0.20, the dielectric and piezoelectric properties decrease rapidly, which is not desirable.

[0092] In Example 1 of the present invention, [Pb 0.98-1.5x Ba 0.02 Sr0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0.0≤x≤0.04 [Donor content]; 0.0≤z≤0.03 [Oxygen vacancy content]) and in Example 2 [Pb 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02 [Donor content]; 0 <z≤0.02 [산소 공공 함량])를 압전 단결정의 일례로 설명하고 있으나, 상기 조성 및 조성비는 이에 한정되지 아니하고 화학식 1의 조성범위 내에서 다양한 변형 및 수정이 가능할 것이다.

[0093] Figure 1 and Figure 4 are photographs of the internal microstructure of a piezoelectric single crystal of a perovskite type crystal structure manufactured in Example 1 or Example 2, and it can be confirmed that secondary phases (MgO, liquid phase, pores, etc.) are mixed inside the single crystal.

[0094] Through the embodiment of the present invention, the piezoelectric single crystal manufactured by the solid-state single crystal growth method has a volume fraction (%) of the secondary phase and an average size of the secondary phase [D 50 ] The high dielectric constant (K3) of piezoelectric single crystals changes with T ) and piezoelectric constant (d 33 ) can be controlled [Table 1 and Table 2]. At this time, the volume fraction (%) of the secondary phase and the average size of the secondary phase [D 50 ] The controlled piezoelectric properties according to the change are confirmed to be at a level similar to the dielectric constant and piezoelectric constant when poled by an external electric field in a typical PMN-PT single crystal.

[0095] Therefore, the piezoelectric properties of the piezoelectric single crystal of the present invention are spontaneous poling properties that have high piezoelectric properties on their own without poling treatment by an external electric field, and since these properties are repeatedly poled, the present invention can provide a new piezoelectric single crystal with high resistance to the external environment.

[0096] Figure 5 shows the Curie temperature (T) of a ferroelectric piezoelectric single crystal of a perovskite type crystal structure according to Example 1 of the present invention. C ) was repeatedly heat-treated five times up to 250℃, and the dielectric constant change curve according to the temperature measured at the fifth time is shown. As a result, the room temperature piezoelectric constant (d) of the single crystal itself 33 ) is 500 pC / N or more, more preferably 1,000 pC / N or more, and most preferably 1,600 pC / N or more, the dielectric constant (K3) at room temperature even after repeated heat treatments above the Curie temperature T ) and piezoelectric constant (d 33 ) does not decrease, it can be confirmed that the result is recovered through spontaneous falling during the cooling process to room temperature after passing through the R / T / C crystal structure.

[0097] In addition, Fig. 6 shows the Curie temperature (T) of a ferroelectric piezoelectric single crystal of a perovskite type crystal structure according to Example 2 of the present invention. C ) is a temperature-dependent dielectric constant change curve measured while repeatedly heat-treating 5 times up to 250℃, and the dielectric constant (K3) at room temperature is the same even after heat treatment above the Curie temperature. T ) shows no decrease in results.

[0098] Therefore, the piezoelectric constant (d) of the single crystal itself 33 ) of a piezoelectric single crystal having a temperature of 500 pC / N or higher, and then heat-treated above the Curie temperature, and then cooled to room temperature, the piezoelectric constant (d) is compared with the temperature change. 33 ) By showing the results that the values ​​match [Table 6], it is possible to confirm thermal stability by inducing spontaneous poling characteristics during the cooling process to room temperature. At this time, the temperature range is 10 to 250℃.

[0099] From the above, the ferroelectric piezoelectric single crystal of the perovskite type crystal structure of the present invention has a Curie temperature (T) without poling treatment by an external electric field. C ) and then cooled to room temperature, the piezoelectric charge constant (d) at room temperature before heat treatment 33 ) has a characteristic that maintains more than 80% of its characteristics.

[0100] In addition, the Curie temperature (T) of the ferroelectric piezoelectric single crystal of Example 2 having the above characteristics was measured after poling treatment. C ) In the results of the heat treatment process repeated five times up to 250℃, the piezoelectric properties increased due to poling decreased in the first heat treatment, and the room temperature properties before poling were maintained after the second heat treatment [Table 7]. Therefore, the ferroelectric piezoelectric single crystal of the perovskite type crystal structure of the present invention has a Curie temperature (T) after poling treatment. C ) and cooled back to room temperature, the piezoelectric charge constant (d) at room temperature before poling treatment 33 ) has a characteristic that maintains more than 80% of its characteristics.

[0101] On the other hand, Fig. 7 shows the same experimental results for a general PMN-PT single crystal according to Comparative Example 1 of the present invention, and the piezoelectric constant (d) of the piezoelectric single crystal measured at room temperature before the poling treatment. 33 ) are all piezoelectric single crystals with values ​​less than 30 pC / N, and the Curie temperature (T C ) after heat treatment at room temperature (K3) T ) As we see the results of lowering the value, it is difficult to use in practice.

[0102] The present invention manufactures piezoelectric single crystals containing a secondary phase within a single crystal using a solid-state single crystal growth method that does not utilize a melting process. In the solid-state single crystal growth method, single crystal growth occurs below the melting temperature, thereby suppressing chemical reactions between the secondary phase and the single crystal, allowing the secondary phase to exist stably and independently within the single crystal.

[0103] In addition, single crystal growth occurs in a polycrystal containing a secondary phase, and there is no change in the volume fraction, size, shape, arrangement, and distribution of the secondary phase during single crystal growth. Therefore, in the process of making a polycrystal containing a secondary phase, by controlling the volume fraction, size, shape, arrangement, and distribution of the secondary phase within the polycrystal and growing the single crystal, a single crystal containing the secondary phase of the desired shape (second phase-including single crystals) can be manufactured.

[0104] In particular, the present invention provides a ferroelectric piezoelectric single crystal having spontaneous poling characteristics, that is, a ferroelectric piezoelectric single crystal that exhibits high piezoelectric characteristics without poling treatment by an external electric field only under specific conditions of the secondary phase and the electrical defects coexisting within the single crystal.

[0105] In the ferroelectric piezoelectric single crystal of the present invention, two or more secondary phases selected from a metal phase, an oxide phase, or a pore are mixed. Specifically, the secondary phase may be a metal phase, an oxide phase, or a pore, and more specifically, it is at least two or more selected from the group consisting of Au, Ag, Ir, Pt, Pd, Rh, MgO, ZrO2, and a pore, and more preferably, it includes one selected from the metal phase or the oxide phase and a pore.

[0106] The above secondary phase is uniformly distributed in the form of particles within the piezoelectric single crystal or is regularly distributed in a certain pattern.

[0107] The average size of the above secondary phase (D 50 ) is preferably 1 to 20㎛, and the volume fraction inside the single crystal is 2 to 12% by volume. At this time, the fraction of pores inside the piezoelectric single crystal can be 50% by volume or more compared to the entire secondary phase.

[0108] The volume fraction of the secondary phase is high compared to single crystal or polycrystalline ceramics manufactured by the conventional flux method and Bridgman method. The process for increasing the volume fraction of the secondary phase is generally to first mold powder to produce a molded body, and then heat-treat the molded body to manufacture a single crystal. This is a method of using high pressure during the molding process to maximize the density of the molded body. At this time, if the density of the molded body is high, the density of the sintered body or single crystal after the heat treatment also increases, so if the pressure is intentionally lowered during molding, the density of the molded body, sintered body, and single crystal decreases. In other words, the fraction of pores increases. Therefore, by lowering the molding pressure during molding, the fraction of pores inside the single crystal can be increased.

[0109] Another process involves using organic materials that burn out at low temperatures. Specifically, after powder manufacturing, organic materials are mixed into the powder and molded. This process results in the molded body containing the organic materials. Subsequent heat treatment causes the organic materials to burn out at a temperature lower than the sintering temperature (approximately 200-600°C), leaving pores in their place. If heat treatment is performed at the temperature at which single crystals grow, densification cannot be sufficiently achieved within these pores, resulting in increased porosity. Therefore, increasing the content of organic materials can proportionally increase the porosity within the single crystal.

[0110] Furthermore, general heat treatment conditions, sintering conditions, and single crystal manufacturing conditions represent conditions suitable for producing high-density single crystals. If single crystals are manufactured under conditions (temperature, heating rate, heat treatment atmosphere, additives, liquid phase, secondary phase, etc.) different from these optimal conditions, the density naturally decreases and the porosity increases. Therefore, in the single crystal manufacturing process, the porosity within the single crystal can be increased simply by changing other conditions (temperature, heating rate, heat treatment atmosphere, additives, liquid phase, secondary phase, etc.).

[0111] The present invention provides a method for manufacturing a piezoelectric single crystal using a solid-state single crystal growth method. The solid-state single crystal growth method is based on patent documents 1 and 2, and piezoelectric single crystals grown using the solid-state single crystal growth method can be mass-produced at a lower process cost than those grown using the flux method and the Bridgman method.

[0112] Specifically, the method for manufacturing the piezoelectric single crystal of the present invention is

[0113] (a) a step of reducing the number density (number of abnormal grains / unit area) of abnormal grains by controlling the average size of matrix grains of a polycrystal having a composition constituting the piezoelectric single crystal; and

[0114] (b) A method for manufacturing a piezoelectric single crystal is provided, comprising: a step of heat-treating a polycrystal having a reduced number density of abnormal particles obtained through the above step (a) to grow abnormal particles; wherein a powder having a composition of [A] site ions and [B] site ions constituting the piezoelectric single crystal is calcined at a temperature of 600 to less than 1,000°C to obtain a powder molded body; a first heat treatment process for sintering the powder molded body and a second heat treatment process during the single crystal growth are performed; and a secondary phase is controlled to be included in the powder molded body at a volume fraction of 2 to 12% by volume.

[0115] In addition, the average size of the above secondary phase [D 50 ] is preferably adjusted to 2 to 20㎛.

[0116] In the method for manufacturing a piezoelectric single crystal of the present invention, the first and second heat treatment processes are performed at 900 to 1,300°C for 1 to 1,000 hours, and it is preferable that the heat treatment is performed at a heating rate of 1 to 20°C / min.

[0117] The above heat treatment can be performed by controlling the oxygen partial pressure. At this time, the oxygen partial pressure control can be performed under air conditions, N2 atmosphere, or H2-N2 atmosphere, and depending on the oxygen partial pressure conditions during the heat treatment, the coercive field (E C ) and internal electric field (E I ) can control the properties.

[0118] Specifically, as the oxygen partial pressure in the above atmosphere decreases, the electric field (E C ) and internal electric field (E I ) is implemented with properties that tend to increase.

[0119] Accordingly, if single crystal growth is not sufficient or is promoted by the first and second heat treatments, the oxygen vacancy content in the piezoelectric single crystal can be controlled by further performing a third heat treatment on the grown single crystal.

[0120] At this time, the third heat treatment process may vary in temperature and time depending on the oxygen atmosphere, but may preferably be performed at 600 to 1,300°C for 0.1 to 100 hours. After the single crystal growth process, the oxygen vacancy content (0) is increased depending on the oxygen partial pressure conditions in the atmosphere during the additional third heat treatment process. <z≤0.03)이 조절하여 압전 단결정을 제조할 수 있다.

[0121] Therefore, by controlling the atmosphere [size of oxygen partial pressure] during the single crystal growth heat treatment process, it is possible to sufficiently induce spontaneous poling characteristics that are not present in general PMN-PT single crystals, thereby manufacturing a new piezoelectric single crystal with high resistance to external environments.

[0122] Conventional single crystal growth methods, such as the flux method and the Bridgman method, cannot produce a piezoelectric single crystal with a composite composition in the perovskite type crystal structure ([A][B]O3). In particular, in the case of the flux method and the Bridgman method, which include a melting process, the composition gradient within the single crystal is produced to be 1 to 5 mol% or more during the manufacturing process, whereas the solid-state single crystal growth method of the present invention can produce a uniform composition with a composition gradient within the single crystal of 0.2 to 0.5 mol%.

[0123] Therefore, the present invention uniformly grows a piezoelectric single crystal in a perovskite crystal structure ([A][B]O3) containing lead zirconate by a solid-state single crystal growth method, even if the composition of the [A] site ion and the combination of the [B] site ions are complex, thereby achieving a high piezoelectric constant (d) without poling treatment compared to conventional piezoelectric single crystals. 33 ≥500 to 5,000 pC / N) and high internal electric fields (E C ≤1.0 kV / cm) and has a dielectric constant (Dielectric Constant, K3) T ) can provide a ferroelectric piezoelectric single crystal satisfying 1,500 to 8,000.

[0124] In particular, the above-mentioned anti-electromagnetic field (E C ) is 2.0 kV / cm or more, more preferably 3 to 10 kV / cm, and if the resistive field is less than 2.0 kV / cm, there is a problem that polling is easily eliminated when processing a piezoelectric single crystal or when manufacturing or using a piezoelectric single crystal application part.

[0125] In addition, the internal bias electric field (E) of the ferroelectric piezoelectric single crystal of the perovskite type crystal structure ([A][B]O3) of the present invention I ) is 1.0 kV / cm or less, more preferably 0.5 kV / cm, so that the piezoelectric charge constant (d) of the single crystal 33 ) has the advantage of enabling it to be increased to the range of 500 to 5,000 pC / N.

[0126] The above method for manufacturing a piezoelectric single crystal controls the composition of [A] site ions and [B] site ions in a piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3), and controls the oxygen partial pressure during heat treatment in the manufacturing process, thereby allowing electrical defects and secondary phases to coexist inside the single crystal, and significantly increasing the effect of electrical defects under specific secondary phase conditions inside the single crystal, thereby maintaining the high dielectric constant and piezoelectric constant inherent to the piezoelectric single crystal without poling treatment by an external electric field.

[0127] Furthermore, the present invention provides piezoelectric application components and dielectric application components using a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having the above-described spontaneous poling characteristics.

[0128] In addition, the present invention provides a piezoelectric single crystal composite in which a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having the above-described spontaneous poling characteristics is mixed with a polymer, and provides a piezoelectric application component and a dielectric application component using the piezoelectric single crystal composite.

[0129] The above piezoelectric application components include ultrasonic transducers (medical ultrasound diagnostic devices, sonar transducers, non-destructive testing transducers, ultrasonic cleaners, ultrasonic motors, etc.), piezoelectric actuators (d 33 Type actuator, d 31 Type actuator, d 15There are piezoelectric actuators (such as piezoelectric actuators for micro-position control, piezoelectric pumps, piezoelectric valves, and piezoelectric speakers), piezoelectric sensors (such as piezoelectric accelerometers), electric field generating transducers, and electric field and vibration generating transducers.

[0130] Additionally, genetic application components include high-efficiency capacitors, infrared sensors, and dielectric filters.

[0131] The above piezoelectric application components and dielectric application components utilize the thermal stability of a piezoelectric single crystal with spontaneous poling characteristics, so that they can be used stably without degradation of characteristics under a wide range of usage conditions (temperature, electric field, pressure, etc.) without shock from excessive temperature or pressure during the manufacturing process or use.

[0132] Hereinafter, the present invention will be described in more detail through examples.

[0133] These examples are intended to explain the present invention more specifically, and the scope of the present invention is not limited to these examples.

[0134] <Example 1> Manufacturing of piezoelectric single crystals with controlled secondary phase fraction 1

[0135] [Pb] by solid-state single crystal growth method 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z(0.0≤x≤0.04 [Donor content]; 0.0≤z≤0.03 [Oxygen vacancy content]) Piezoelectric single crystals were manufactured. Excess MgO and PbO were added in the powder synthesis process, and the content of secondary phases (MgO, liquid phase and pores, etc.) inside the manufactured single crystals was changed from 1 to 20 vol% by changing the amount of excess MgO and PbO, [Pb 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0.0≤x≤0.04; 0.0≤z≤0.03) Ceramic powders were manufactured using the Coulombite method. First, MgO and Nb2O5 powders were ball milled and mixed, and then calcined to manufacture the MgNb2O6 phase. Additionally, the raw material powders were mixed again in a fixed quantitative ratio and calcined to manufacture perovskite phase powders (calcination process). Excess MgO and PbO were added to the manufactured powders to manufacture mixed powders. At this time, in order to change the content of secondary phases (MgO, liquid phase, pores, etc.) inside the single crystal from 1 to 20 vol%, the amounts of excess MgO and PbO were increased in the powder synthesis process.

[0136] After molding the above mixed powders, they were pressurized with a hydrostatic pressure of 200 MPa, and the powder molded bodies were heat-treated at various temperature conditions between 900°C and 1300°C at intervals of 25°C for up to 100 hours. The average size (R) of the matrix particles of the polycrystal was set to a size range of 0.5 to 2 times the critical size at which abnormal particles were generated (0.5R c ≤R≤2R c ), the amount of excess PbO added was determined to be in the range of 5 to 20 mol%, and the heat treatment temperature was determined to be in the range of 1000 to 1250°C (sintering process, first heat treatment). Ba(Ti) was added to the polycrystal manufactured in this way.0.7 Zr 0.3 )O3 seed single crystals were placed and heat-treated (single crystal growth heat treatment, second heat treatment), and the continuous growth of the seed single crystals into the polycrystal was used to determine the polycrystal composition. A single crystal was manufactured.

[0137] The average size (R) of the matrix particles of the above polycrystal is the critical size at which abnormal particles are generated (the average size of the matrix particles at which the number density of abnormal particles becomes "0 (zero)", R c ) is 0.5 times or more and 2 times or less in size range (0.5R) c ≤R≤2R c ), the seed single crystals grew continuously into the polycrystal. In this example, when the amount of excess PbO and the heat treatment temperature were adjusted, the average size (R) of the matrix particles of the polycrystal could be adjusted to a size range of 0.5 to 2 times the critical size at which abnormal particles were generated. The average size (R) of the matrix particles of the polycrystal was adjusted to 0.5R c ≤R≤2R c When adjusted to the range of Ba(Ti) during heat treatment 0.7 Zr 0.3 )O3 seed single crystals were continuously grown inside the polycrystal, and a single crystal with the same composition as the polycrystal was manufactured, and the size of the grown single crystal was 20×20 mm. 2 That was it.

[0138] During the above single crystal production process [powder calcination process, sintering process of powder compact (first heat treatment), single crystal growth process (second heat treatment)], the oxygen vacancy content [z] was controlled by controlling the oxygen partial pressure in the atmosphere, and the grown single crystal was additionally heat treated [third heat treatment] to ultimately obtain various [Pb] in the range of "0.0≤z≤0.03". 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr0.30 Ti 0.35 ]O 3-z (0.0≤x≤0.04; 0.0≤z≤0.03) Piezoelectric single crystals were manufactured.

[0139] Figures 1 and 2 are photographs of the internal microstructure of a piezoelectric single crystal of a perovskite type crystal structure manufactured in Example 1. It was confirmed that secondary phases (MgO, liquid phase, pores, etc.) were mixed inside the single crystal, and in particular, in the case of a high secondary phase fraction, secondary phases of various types and sizes were mixed.

[0140] <Example 2> Manufacturing of piezoelectric single crystals including secondary phase fraction control and oxygen vacancies 2

[0141] [Pb] by solid-state single crystal growth method 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02 [Donor content]; 0 <z≤0.02 [산소 공공 함량]) 압전 단결정을 제조하였다. 분말 합성 공정에서 과량의 MgO, PbO와 내부 전기장을 크게 조절하기 위하여, 억셉터 첨가제로 MnO를 추가하여, 제조된 단결정 내부에는 이차상(MgO, 기공 등)이 5 부피% 정도 되도록 조절하여, [Pb 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z(0≤x≤0.02; 0 <z≤0.02) 조성의 세라믹 분말을 쿨롬바이트(Columbite)법을 이용하여 제조하는 것을 제외하고는, 상기 실시예 1과 동일하게 수행하여 압전 단결정을 제조하되, 상기 단결정 제작 공정[분말 하소 공정, 분말 성형체의 소결 공정 (1차 열처리), 단결정 성장 공정(2차 열처리)] 중에 분위기 내의 산소 분압을 조절하여 산소 공공 함량[z]를 조절하였고, 성장된 단결정을 추가적으로 열처리[3차 열처리]하여 최종적으로 "0<z≤0.02"의 범위에서 다양한 [Pb 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02; 0 <z≤0.02) 압전 단결정들을 제조하였다.

[0142] Figure 3 is a photograph of a piezoelectric single crystal of a perovskite type crystal structure manufactured in Example 2 of the present invention. The appearance of the single crystal may vary depending on the change in the composition ratio of the donor and acceptor and the atmosphere during single crystal growth, and [Pb 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02; 0≤z≤0.02) The piezoelectric single crystal is a single crystal growth atmosphere (Air) and is black due to the addition of Mn.

[0143] In addition, FIG. 4 is a microscopic photograph of a piezoelectric single crystal of a perovskite type crystal structure manufactured in Example 1 of the present invention, and it was confirmed that secondary phases (pores, liquid phase, MgO, etc.) were mixed inside the single crystal.

[0144] <Comparative Example 1>

[0145] Conventional PMN-PT single crystal ([Pb][(Mg 1 / 3 Nb 2 / 3 ) 0.7 Ti 0.3 ]O3) was prepared.

[0146] <Experimental Example 1> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 1-1

[0147] [Pb] prepared in the above Example 1 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0.0≤x≤0.04; 0.0≤z≤0.03) For piezoelectric single crystals, the average size of the secondary phase is about 5㎛, and the dielectric constant, piezoelectric constant, and internal electric field (E) of the piezoelectric single crystals manufactured according to the change in the volume fraction of the secondary phase I ) were measured using an impedance analyzer, etc. according to the IEEE method and are listed in Table 1 below.

[0148] Table 1

[0149]

[0150] From the results in Table 1 above, [Pb 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z In a piezoelectric single crystal with a composition of (0.0≤x≤0.04; 0.0≤z≤0.03), the dielectric constant (K3) varies with the volume fraction of the secondary phase. T ), piezoelectric constant (d 33 ) and internal electric field (E I ) value change was confirmed.

[0151] In particular, when the volume fraction of the secondary phase is 2 to 12 vol%, the piezoelectric constant (d) due to spontaneous polarization 33 ) was induced to be higher than 500 pC / N, more preferably higher than 1,000 pC / N, and at this time, the internal electric field (E I ) was induced at low levels, ranging from 0.1 to 0.35 kV / cm.

[0152] In addition, when manufacturing the piezoelectric single crystals of Example 1, the volume fraction of the secondary phase was fixed at 8% by volume, and the dielectric constant, piezoelectric constant, and internal electric field (E) of the piezoelectric single crystals according to the change in the average size of the secondary phase I ) were measured using an impedance analyzer, etc. according to the IEEE method and are listed in Table 2 below.

[0153] Table 2

[0154]

[0155] From the results in Table 2 above, [Pb 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z In a piezoelectric single crystal with a composition of (0.0≤x≤0.04; 0.0≤z≤0.03), the dielectric constant (K3) varies with the average size of the secondary phase. T ), piezoelectric constant (d 33 ) and internal electric field (E I ) value change was confirmed.

[0156] In particular, the average size of the secondary phase [D 50 ] is 2 to 20 μm, the piezoelectric constant (d) due to spontaneous polarization 33 ) was induced to be higher than 500 pC / N, more preferably higher than 1,000 pC / N, and at this time, the internal electric field (E I) was induced at low levels of 0.13 to 0.25 kV / cm.

[0157] From the above, the volume fraction (%) of the secondary phase and the average size of the secondary phase [D 50 ] according to the change in dielectric constant (K3 T ), piezoelectric constant (d 33 ) and internal electric field (E I ) was confirmed to be able to control the value.

[0158] <Experimental Example 2> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 1-2

[0159] [Pb] prepared in the above Example 1 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z Among the piezoelectric single crystals with a perovskite crystal structure (0.0≤x≤0.04; 0.0≤z≤0.03), three measurement specimens (11, 12, 13) were prepared with a size of 0.5 mm in thickness, 3.00 mm in width, and 3.00 mm in length.

[0160] In the above piezoelectric single crystals, the dielectric constant and phase transition temperatures (T) according to the change in x [donor content] and z [oxygen vacancy content] C Wow T RT ), piezoelectric constant, coercive field (E C ) and internal electric field (E I ) were measured using an impedance analyzer and other devices according to the IEEE method and are listed in Table 3.

[0161] Table 3

[0162]

[0163] The figures in Table 3 above are piezoelectric constants measured at room temperature without poling treatment, and the piezoelectric constant (d) is about 1,600 pC / N on average even though no separate poling treatment was performed after the single crystal growth process. 33 ) was confirmed. And the hydrostatic piezoelectric constant (d h ) showed a high value of over 1,000 pC / N, and the internal electric field was low at an average of less than 0.2 kV / cm.

[0164] Therefore, in the above Example 1, when manufacturing a piezoelectric single crystal by a solid-state single crystal growth method, the volume fraction (%) of the secondary phase and the average size of the secondary phase [D 50 ] High dielectric constant (K3) of piezoelectric single crystals controlled by change T ) and piezoelectric constant (d 33 ) values ​​were confirmed to be similar to the dielectric constant and piezoelectric constant when the PMN-PT single crystal was poled by an external electric field. At this time, the average size of the secondary phase [D ] in the single crystal was in the range of 2 to 12 volume%. 50 ] is preferably controlled in the range of 2 to 20 ㎛ [Table 1 and Table 2].

[0165] The volume fraction (%) of the secondary phase and the average size of the secondary phase [D 50 ] The dielectric constant and piezoelectric constant characteristics of the piezoelectric single crystal controlled by the change are induced by spontaneous poling with high piezoelectric properties without poling treatment by an external electric field, and it was confirmed that these characteristics can be used to manufacture a new piezoelectric single crystal with high resistance to the external environment by being repeatedly poled.

[0166] <Experimental Example 3> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 1-3

[0167] [Pb] prepared in the above Example 1 0.98-1.5x Ba 0.02 Sr 0.01 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr0.30 Ti 0.35 ]O 3-z (0.0≤x≤0.04; 0.0≤z≤0.03) For the piezoelectric single crystals, "11" among the single crystal specimens in Table 3 above is selected for the Curie temperature (T C ) After repeated heat treatment up to 250℃ five times, the piezoelectric constant was measured at room temperature (20℃) and recorded in Table 4 below.

[0168] Table 4

[0169]

[0170] As a result of the above Table 4, even after repeated heat treatment, the piezoelectric constant (d) which is the dielectric property at room temperature 33 ), dielectric constant (K3 T ) did not decrease, but rather the piezoelectric constant at room temperature (d 33 ) increased by about 10% of the characteristics.

[0171] Figure 5 shows a dielectric constant change curve according to temperature measured for the fifth time, showing that the room temperature characteristics are recovered again through spontaneous poling even after the fifth heat treatment.

[0172] From the above results, the piezoelectric single crystal manufactured in Example 1 has a volume fraction (%) of the secondary phase and an average size of the secondary phase [D 50 ] is controlled by the room temperature piezoelectric constant (d) of the single crystal itself. 33 ) is 500 pC / N or more, more preferably 1,000 pC / N or more, and most preferably 1,600 pC / N or more, even after repeated heat treatments above the Curie temperature, the dielectric constant (K3) at room temperature T ) and piezoelectric constant (d 33 ) was not reduced, and thermal stability was confirmed to be recovered through spontaneous poling during cooling to room temperature after passing through the R / T / C crystal structure.

[0173] <Experimental Example 4> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 2-1

[0174] [Pb] prepared in the above Example 20.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02; 0 <z≤0.03) 압전 단결정들에 대하여, 두께 0.5㎜, 폭 3.00㎜ 및 길이 3.00㎜ 크기로 측정 시편 5개(21, 22, 23, 24, 25)를 준비하였다.

[0175] The above manufactured [Pb 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02; 0 <z≤0.03) 압전 단결정들에서 x[Donor 함량]와 z[산소 공공 함량]의 변화에 따른 유전 상수, 상전이 온도들(T C Wow T RT ), piezoelectric constant, coercive field (E C ) and internal electric field (E I ) were measured using an impedance analyzer and other devices according to the IEEE method and are listed in Table 5.

[0176] Table 5

[0177]

[0178] The values ​​in Table 5 for the piezoelectric single crystals manufactured in the above Example 2 are piezoelectric constants measured at room temperature without poling treatment, and the piezoelectric constant (d) is about 900 pC / N on average even though poling treatment, which applies an external electric field, was not performed even once after the single crystal growth process. 33 ) was confirmed. And the hydrostatic piezoelectric constant (d h ) showed a high value of more than 400 pC / N, and the internal electric field was low at an average of less than 0.5 kV / cm.

[0179] <Experimental Example 5> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 2-2

[0180] [Pb] prepared in the above Example 2 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02; 0 <z≤0.03) 압전 단결정들에 대하여, 상기 표 5의 단결정 시편 중 "21"을 큐리 온도(T C ) After repeated heat treatment up to 250℃ five times, the piezoelectric constant was measured at room temperature (20℃) and recorded in Table 6 below.

[0181] Table 6

[0182]

[0183] As a result of the above Table 6, even after repeated heat treatment, the piezoelectric constant (d) which is the dielectric property at room temperature 33 ), dielectric constant (K3 T ) and the piezoelectric constant (d) at room temperature is not reduced. 33 ) More than 95% of the characteristics were maintained.

[0184] Figure 6 shows the Curie temperature (T) of the piezoelectric single crystal specimen “21” manufactured in Example 2. C ) It shows the results of the change in dielectric constant according to temperature measured while repeatedly heat-treating 5 times up to 250℃.

[0185] From the above results, the piezoelectric constant (d) of the single crystal itself 33 ) of the piezoelectric single crystal manufactured in Example 2 having a dielectric constant of 500 pC / N or more was repeatedly heat-treated without poling treatment, and the dielectric constant change curve according to temperature was measured. Even after heat treatment above the Curie temperature, the dielectric constant (K3) at room temperature was T ) does not decrease, and the piezoelectric constant (d) for temperature change after passing through the R / T / C crystal structure 33) showed consistent results, confirming thermal stability due to spontaneous poling characteristics induced during cooling to room temperature. At this time, thermal stability was confirmed in the temperature range of 10 to 250°C.

[0186] <Experimental Example 6> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 2-3

[0187] [Pb] prepared in the above Example 2 0.98-1.5x Ba 0.02 Sm x ][(Mg 1 / 3 Nb 2 / 3 ) 0.35 Zr 0.30 Ti 0.35 ]O 3-z (0≤x≤0.02; 0 <z≤0.03) 압전 단결정으로부터 제작된 시편"23"을 1차 폴링 후 상온 특성을 측정하고, 큐리 온도(T C ) After repeated heat treatment up to 250℃ five times, the piezoelectric constant was measured at room temperature (20℃) and the results are shown in Table 7.

[0188] Table 7

[0189]

[0190] As a result of Table 7 above, the piezoelectric constant (d) in the first heat treatment after poling 33 ), dielectric constant (K3 T ) decreases, but it was confirmed that the piezoelectric properties at room temperature before poling were maintained after the second heat treatment. Therefore, it was confirmed that the piezoelectric properties that were reduced in the first heat treatment after poling were reduced by the amount of the piezoelectric properties that increased due to poling, and that the inherent high piezoelectric properties of the piezoelectric single crystal were maintained.

[0191] From the above, in the perovskite type crystal structure ([A][B]O3) designed in the present invention, the donor content and acceptor content control, the volume fraction (%) of the secondary phase, and the average size of the secondary phase [D 50] According to the change, electrical defects and secondary phases coexist inside the ferroelectric piezoelectric single crystal, and the effect of electrical defects is greatly increased under specific secondary phase conditions (type, size, and fraction) inside the single crystal, and the piezoelectric properties are maintained during the cooling process to room temperature after heat treatment above the Curie temperature without poling treatment by an external electric field, and the thermal stability is shown. At this time, the piezoelectric constant (d 33 ) maintained high piezoelectric properties of 500 to 3,000 pC / N.

[0192] <Experimental Example 7> Evaluation of Dielectric and Piezoelectric Properties of Piezoelectric Single Crystals 3-1

[0193] Typical PMN-PT single crystal ([Pb][(Mg 1 / 3 Nb 2 / 3 ) 0.7 Ti 0.3 ]O3) Five specimens (31, 32, 33, 34, 35) each manufactured with a thickness of 0.5 mm, a width of 3.00 mm, and a length of 3.00 mm were prepared, and the changes in dielectric properties using the same method are described in Table 8 below.

[0194] Table 8

[0195]

[0196] As confirmed in the results in Table 8 above, all of the piezoelectric constants measured at room temperature before the first poling treatment are low (d 33 ) was confirmed to be less than 300 pC / N.

[0197] In addition, Fig. 7 shows the Curie temperature (T) of PMN-PT single crystal specimen "31" of Comparative Example 1. C ) It shows the change in dielectric constant according to temperature measured while repeatedly heat-treating 5 times up to 250℃, which is higher than the Curie temperature (T C ) after heat treatment at room temperature (K3) T ) results in lower values. Therefore, it is difficult to use in practice.

[0198] Although the present invention has been described in detail above only with respect to the described specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical scope of the present invention, and it is natural that such modifications and variations fall within the scope of the appended claims.

Claims

1. Piezoelectric charge constant (d) of single crystal 33 ) is 500 to 5,000 pC / N, Internal Bias Electric Field (E) of a single crystal I ) meets the piezoelectric properties of 1.0 kV / cm or less, A ferroelectric piezoelectric single crystal with a perovskite crystal structure ([A][B]O3) having a secondary phase mixed in at 2 to 12 volume% within the single crystal and having spontaneous poling characteristics.

2. In the first paragraph, the average size of the secondary phase [D 50 ] A ferroelectric piezoelectric single crystal having a perovskite type crystal structure characterized by a diameter of 2 to 20 μm.

3. A ferroelectric piezoelectric single crystal having a perovskite crystal structure ([A][B]O3), characterized in that the internal electric field (Internal Bias Electric Field, EI) of the single crystal in the first paragraph is 0.5 kV / cm or less.

4. In the first paragraph, the piezoelectric single crystal has a hydrostatic piezoelectric constant (d h ) A ferroelectric piezoelectric single crystal having a perovskite crystal structure characterized by a tensile strength of 200 to 1,500 pC / N.

5. A ferroelectric piezoelectric single crystal having a perovskite crystal structure, characterized in that the piezoelectric single crystal in the first paragraph has spontaneous poling characteristics in a temperature range of 10 to 250°C.

6. A ferroelectric piezoelectric single crystal having a perovskite crystal structure, characterized in that the secondary phase in the first paragraph is a mixture of two or more types selected from a metal phase, an oxide phase, and a pore phase.

7. A ferroelectric piezoelectric single crystal having a perovskite crystal structure, characterized in that the pores in the 6th paragraph are 50% by volume or more compared to the total volume occupied by the secondary phase.

8. In the first paragraph, a ferroelectric piezoelectric single crystal having a perovskite type crystal structure characterized in that the piezoelectric single crystal has a composition formula of the following chemical formula 1: Chemical Formula 1 [TO 1-(a+1.5b) B a C b ][(MN) 1-x-y (THE) y You x ]OR 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 a single or mixed form selected from Zr or Hf, M is at least one species selected from the group consisting of Ce, Co, Fe, In, Mg, Mn, Ni, Sc, Yb and Zn, N is at least one species 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 및 0≤z≤0.03이다.

9. In the 8th paragraph, a piezoelectric single crystal having a perovskite type crystal structure characterized by having a composition formula of chemical formula 2 when L is in a mixed form in the piezoelectric single crystal: Chemical Formula 2 [AND 1-(a+1.5b) B a C b ][(MN) 1-x-y (Zr 1-w ,Hf w ) y You x ]ON 3-z In the above, A, B, C, M and N, a, b, x, y and z are the same as in chemical formula 1, except that 0.01≤w≤0.

20. 10.(a) A step of reducing the number density (number of abnormal grains / unit area) of the abnormal grains by controlling the average size of the matrix grains of the polycrystal having a composition constituting a piezoelectric single crystal of the perovskite type crystal structure ([A][B]O3). (b) a step of heat-treating the polycrystal with a reduced number density of abnormal particles obtained through the above step (a) to grow abnormal particles, A powder having a composition of [A] site ions and [B] site ions constituting the above piezoelectric single crystal is calcined at a temperature of 600 to less than 1,000°C to obtain a powder molded body, and a first heat treatment process for sintering the powder molded body and a second heat treatment process during the growth of the single crystal are performed. A method for manufacturing a piezoelectric single crystal according to claim 1, characterized in that the secondary phase is included in the powder molded body at a volume fraction of 2 to 12% by volume.

11. In the 10th paragraph, the secondary phase has an average size [D 50 ] A method for manufacturing a piezoelectric single crystal characterized by containing 2 to 20㎛.

12. A method for manufacturing a piezoelectric single crystal, characterized in that the first and second heat treatment processes in the 10th paragraph are performed at 900 to 1,300°C for 1 to 1,000 hours.

13. A method for manufacturing a piezoelectric single crystal, characterized in that, in the 10th paragraph, a third heat treatment process is further performed at 600 to 1,300°C for 0.1 to 100 hours after completion of the single crystal growth.

14. In the 13th paragraph, the oxygen vacancy content (0) is determined by the oxygen partial pressure condition during the third heat treatment process. <z≤0.03)이 조절된 것을 특징으로 하는 압전 단결정의 제조방법.

15. A piezoelectric single crystal composite having spontaneous poling characteristics, wherein a ferroelectric piezoelectric single crystal having a perovskite crystal structure ([A][B]O3) having the spontaneous poling characteristics of any one of claims 1 to 9 is mixed with a polymer.

16. A piezoelectric application component and a dielectric application component using a ferroelectric piezoelectric single crystal of a perovskite type crystal structure ([A][B]O3) having the spontaneous poling characteristic of any one of claims 1 to 9.

17. Piezoelectric application components and dielectric application components using a piezoelectric single crystal composite having the spontaneous poling characteristics of Article 15.

18. A piezoelectric application component and a dielectric application component according to claim 16 or 17, characterized in that the piezoelectric application component and the dielectric application component 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.

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