Piezoelectric ceramic laminate

Abstract

To provide a piezoelectric ceramic laminate that exhibits excellent insulation properties under high temperature and high electric field conditions, as well as superior mechanical strength.SOLUTION: The piezoelectric ceramic laminate includes multiple ceramic layers composed mainly of alkali niobate-based perovskite-type oxides, and multiple internal electrodes alternately laminated in one direction. Each ceramic layer is composed of portions sandwiched between adjacent internal electrodes and has an active layer containing Mn2TiO4, and an inactive layer containing Mn4 Nb2O9, disposed at the ends beyond the internal electrodes in the lamination direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric ceramic laminate. [Background technology]

[0002] In recent years, attention has been focused on multilayer piezoelectric ceramic laminates, which are small and can be driven with high displacement even at low voltages. A typical piezoelectric ceramic laminate includes PZT (lead zirconate titanate) ceramic layers, which contain lead, which has a negative impact on the environment, and internal electrodes containing expensive platinum or palladium. Therefore, there is a demand for environmentally friendly, low-cost piezoelectric ceramic laminates. Accordingly, piezoelectric ceramic laminates have been proposed that include internal electrodes primarily composed of Ni, an inexpensive base metal, and lead-free ceramic layers primarily composed of alkali niobate-based perovskite oxides (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5862983 [Patent Document 2] Patent No. 6094682 Summary of the Invention [Problem to be solved by the invention]

[0004] Piezoelectric ceramic laminates are required to be used at high temperatures and under high electric fields (e.g., 100°C, 3 kV / mm), and therefore must exhibit high insulation properties even under such harsh conditions. Furthermore, because mechanical loads are applied to piezoelectric ceramic laminates during operation, they must also have high mechanical strength.

[0005] Although Patent Documents 1 and 2 disclose the above-mentioned conventional piezoelectric ceramic laminates, they do not consider the insulation properties and mechanical strength at high temperatures and in high electric fields.

[0006] An object of the present invention is to provide a piezoelectric ceramic laminate that has excellent insulating properties at high temperatures and in high electric fields, and also has excellent mechanical strength. [Means for solving the problem]

[0007] The means for solving the above problems are as follows: <1> A piezoelectric ceramic laminate in which a plurality of ceramic layers, the main component of which is an alkali niobate-based perovskite oxide, and a plurality of internal electrodes are alternately stacked in one direction, the ceramic layers being sandwiched between adjacent internal electrodes and having an active layer containing Mn2TiO4, and an inactive layer containing Mn4Nb2O9, which is arranged on the end side of the internal electrodes at both ends in the one direction.

[0008] <2> The plurality of internal electrodes are made of the above-mentioned material containing Ni as a main component. <1> The piezoelectric ceramic laminate according to claim 1. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a piezoelectric ceramic laminate that has excellent insulating properties at high temperatures and in high electric fields, and also has excellent mechanical strength. [Brief explanation of the drawings]

[0010] [Figure 1] Cross-sectional view of a piezoelectric ceramic laminate DETAILED DESCRIPTION OF THE INVENTION

[0011] A piezoelectric ceramic laminate according to an embodiment will now be described. Fig. 1 is a cross-sectional view of a piezoelectric ceramic laminate 10. Fig. 1 shows the piezoelectric ceramic laminate 10 applied to a piezoelectric element. The piezoelectric ceramic laminate 10 is formed by stacking a plurality of ceramic layers (piezoelectric layers) 11 and a plurality of internal electrodes 12 alternately in one direction. The piezoelectric ceramic laminate 10 also includes two external electrodes 14 and 15 connected to the internal electrodes 12.

[0012] Each ceramic layer 11 is mainly composed of an alkali niobate perovskite oxide and is composed of an active layer 11a containing Mn2TiO4 and sandwiched between adjacent internal electrodes 12, and an inactive layer 11b containing Mn4Nb2O9 and disposed closer to the ends of the internal electrodes 12 at both ends in the one direction (stacking direction).

[0013] The active layers 11a are sandwiched between the internal electrodes 12 and are displaced when a voltage is applied. As shown in Fig. 1, a plurality of active layers 11a are arranged parallel to each other and sandwiched between the internal electrodes 12 adjacent to each other in the stacking direction.

[0014] 1, the inactive layer 11b is located on the outermost layer and protects the active layer 11a. The inactive layer 11b is a portion that does not displace when a voltage is applied.

[0015] The internal electrodes 12 are mainly composed of a base metal (e.g., nickel). In other embodiments, the internal electrodes 12 may be made of a metal or alloy such as platinum (Pt), silver-palladium (Ag-Pd), or silver (Ag).

[0016] The two external electrodes 14, 15 are made primarily of gold (Au), for example, and are arranged on the outer surfaces of a laminate of a plurality of ceramic layers 11 and a plurality of internal electrodes 12. As shown in Fig. 1, one external electrode 14 is arranged on the outer surface of the right side of the laminate, and the other external electrode 15 is arranged on the outer surface of the left side of the laminate. The plurality of internal electrodes 12 described above are made up of internal electrodes 12a, each of which has an end connected to one external electrode 14, and internal electrodes 12b, each of which has an end connected to the other external electrode 15.

[0017] When a voltage is applied between the external electrodes 14 and 15, the active layer 11a of the ceramic layer 11 sandwiched between the internal electrodes 12 is displaced so as to expand and contract.

[0018] Next, a description will be given of the lead-free piezoelectric composition that constitutes the ceramic layer 11. The active layer 11a and the inactive layer 11b that are the ceramic layer 11 contain alkali niobate perovskite oxide as the main component (main phase).

[0019] <Preferred Subphase Composition> (1)Active layer Preferably, the oxide is a MnTi2O4-based oxide, having a spinel structure or an inverse spinel structure. Furthermore, the ratios of Mn, Ti, and O may deviate from the above ranges as long as the structure can be maintained. Furthermore, as long as the structure can be maintained, other elements may be contained within a range of 10 mol % or less, such as Na, K, Nb, Ti, Zr, Ba, Ca, Sr, Ni, Cu, Ag, and Sc. It is believed that the insulating properties can be improved by using an active layer containing the above-mentioned Mn2TiO4-based oxide. (2) Inactive layer Preferably, the oxide is a Mn4Nb2O9-based oxide, which has a corundum structure. Furthermore, the ratio of Mn, Nb, and O may deviate from the above range as long as the structure can be maintained. Furthermore, as long as the structure can be maintained, other elements may be contained within a range of 10 mol% or less, such as Na, K, Nb, Ti, Zr, Ba, Ca, Sr, Ni, Cu, Ag, and Sc. It is believed that the mechanical strength can be increased by using an inactive layer containing the above-mentioned Mn4Nb2O9-based oxide.

[0020] Alkali niobate perovskite oxides have a perovskite structure and are represented by the general composition formula ABO3. The perovskite structure is generally represented by the composition formula ABO3 and is composed of atoms occupying the A site, atoms occupying the B site, and oxygen (O) atoms. In the perovskite structure, six oxygen atoms are coordinated around the B site atom, and 12 oxygen atoms are coordinated around the A site atom, and this structure is repeated periodically to form a crystal. The alkali niobate perovskite oxide of the present invention preferably contains at least one alkali metal (potassium (K), sodium (Na), lithium (Li), etc.) as an alkaline component at the A site, and particularly preferably contains at least one of potassium (K) and sodium (Na), and preferably contains niobium (Nb) at the B site. Furthermore, the alkali niobate perovskite oxide may contain an alkaline earth metal (at least one of calcium (Ca), strontium (Sr), barium (Ba), etc.) as an alkaline component at the A site. Furthermore, the effects of the present invention can be obtained even if some of the alkali components are located in the B site or niobium is located in the A site. Furthermore, although the composition formula of perovskite metal oxides is generally expressed as ABO3, in reality, due to volatilization during firing and errors in composition analysis, the ratio of the A-site elements, B-site elements, and oxygen elements in the entire metal oxide may not necessarily be 1:1:3. Even in such cases, as long as the oxide has a perovskite structure as its main phase, it is within the scope of the present invention. The fact that the oxide has a perovskite structure can be determined, for example, from the results of X-ray diffraction or electron diffraction measurements on the piezoelectric ceramic. The alkali niobate perovskite oxide of the main phase is preferably a compound represented by the following composition formula (1).

[0021] (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 Sc d5 )O 3+e ···(1)

[0022] In the composition formula (1), the element A1 is at least one of the alkali metals K (potassium), Na (sodium), and Li (lithium), and the element M1 is at least one of the alkaline earth metals Ba (barium), Ca (calcium), and Sr (strontium).

[0023] As the values of the coefficients a to e in the compositional formula (1), among the combinations of values that form a perovskite structure, the electrical properties or piezoelectric properties (especially the piezoelectric constant d 33 ) of the lead-free piezoelectric composition are selected as preferable values from the viewpoint.

[0024] Specifically, the coefficients a and b satisfy 0 < a < 1 and 0 < b < 1, and a = 0 (i.e., a composition containing no alkali metals) and b = 0 (i.e., a composition containing neither Ba, Ca, nor Sr) are excluded.

[0025] The coefficient c with respect to the entire A site satisfies 0.80 < c < 1.10, and 0.99 ≤ c ≤ 1.05 is preferable.

[0026] The coefficients d1, d2, d3, d4, and d5 are preferably 0 < d1 < 1, 0 ≤ d2 < 0.100, 0 ≤ d3 < 0.100, 0 ≤ d4 < 0.200, and 0 ≤ d5 < 0.100.

[0027] Furthermore, the coefficient d1 of Nb is preferably 0.800 ≤ d1 ≤ 0.959. The coefficient d2 of Mn is preferably 0.001 ≤ d2 ≤ 0.800. The coefficient d3 of Ti is preferably 0.005 ≤ d3 ≤ 0.800. The coefficient d4 of Zr is preferably 0 ≤ d4 ≤ 0.150. The coefficient d5 of Sc is preferably 0.0002 ≤ d5 ≤ 0.070.

[0028] Among the coefficients 3 + e of oxygen, the coefficient e is a positive or negative value indicating oxygen deficiency or excess with respect to the coefficient of oxygen, which is usually 3. The coefficient 3 + e of oxygen can take a value that forms a perovskite oxide as the main phase. A typical value of the coefficient e is e = 0, and 0 ≤ e ≤ 0.1 is preferable. The value of the coefficient e can be calculated from the electrical neutrality condition of the composition of the main phase. However, as the composition of the main phase, a composition slightly deviating from the electrical neutrality condition is also acceptable.

[0029] Among the alkali niobate perovskite-type oxides represented by the above compositional formula (1), oxides with K, Na, and Nb as the main metal components are referred to as "KNN" or "KNN material" and are excellent in piezoelectric properties, electrical properties, etc.

[0030] Note that the above compositional formula (1) can be rewritten as the following compositional formula (1A).

[0031] (K a1 Na a2 Li a3 Ba b1 Ca b2 Sr b3 ) c (Nb d1 Mn d2 Ti d3 Zr d4 Sc d5 )O 3+e ···(1A)

[0032] The above compositional formula (1) and compositional formula (1A) are equivalent. The coefficient a1 of K is 0 < a1 ≤ 0.7 (preferably, 0.095 ≤ a1 ≤ 0.665), the coefficient a2 of Na is 0 < a2 ≤ 0.9 (preferably, 0.285 ≤ a2 ≤ 0.855), and the coefficient a_{3} of Li is 0 ≤ a3 ≤ 0.2 (preferably, 0 ≤ a3 ≤ 0.1). Also, the coefficient b1 of Ba is 0 ≤ b1 ≤ 0.20, the coefficient b2 of Ca is 0 ≤ b2 ≤ 0.20, and the coefficient b3 of Sr is 0 ≤ b3 ≤ 0.20.

[0033] In the alkali niobate perovskite-type oxide represented by the above compositional formula (1) or compositional formula (1A), the content ratio of Sc to Ti (Sc / Ti) is 0.004 or more and 8 or less in terms of molar ratio. When the content ratio of Sc to Ti is within such a range, a lead-free piezoelectric composition excellent in piezoelectric properties and excellent in insulation properties under high-temperature conditions can be obtained.

[0034] Furthermore, the alkali niobate perovskite oxide according to this embodiment may contain other elements as necessary. For example, a composition containing at least one of Ta, Ni, Cu, V, Cr, Fe, Co, Zn, Y, Mo, Ru, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Os, and Ir may be added for the purpose of controlling the piezoelectric characteristics, insulating characteristics, sintering temperature, and suppressing grain growth.

[0035] In this embodiment, the proportion of the main phase contained in the lead-free piezoelectric composition constituting the ceramic layer 11 (active layer 11a and inactive layer 11b) is not particularly limited as long as it does not impair the object of the present invention, but for example, it is preferably 70 volume % or more, more preferably 80 volume % or more, and even more preferably 90 volume % or more.

[0036] The lead-free piezoelectric composition constituting the active layer 11a contains MnTiO as a subphase. The proportion of the subphase in the active layer 11a is not particularly limited as long as it does not impair the object of the present invention, but is preferably, for example, 0.3% by volume or more and 30% by volume or less.

[0037] The active layer 11a may contain, as a subphase, a crystalline phase (oxide) other than Mn2TiO4, as long as it does not impair the object of the present invention. It is preferable that the active layer 11a does not contain Mn4Nb2O9 as a subphase.

[0038] The lead-free piezoelectric composition constituting the inactive layer 11b contains MnNbO as a subphase. The proportion of the subphase in the inactive layer 11b is not particularly limited as long as it does not impair the object of the present invention, but is preferably, for example, 0.3% by volume or more and 30% by volume or less.

[0039] The inactive layer 11b may contain, as a subphase, a crystalline phase (oxide) other than Mn4Nb2O9, as long as it does not impair the object of the present invention. It is preferable that the inactive layer 11b does not contain Mn2TiO4 as a subphase.

[0040] A method for manufacturing the above-mentioned piezoelectric ceramic laminate will be described later.

[0041] The piezoelectric ceramic laminate of this embodiment as described above has excellent insulating properties and mechanical strength at high temperatures and high electric fields. Furthermore, the piezoelectric ceramic laminate also has excellent piezoelectric properties at high temperatures and high electric fields. Such piezoelectric ceramic laminates can be widely used in vibration detection, pressure detection, oscillation, piezoelectric device applications, and the like. For example, they can be used in sensors that detect various vibrations (e.g., Knox sensors and combustion pressure sensors), piezoelectric devices such as vibrators, actuators, and filters, high-voltage generators, micropower sources, various driving devices, position control devices, vibration suppression devices, fluid ejection devices (e.g., paint ejection, fuel ejection), and the like. [Example]

[0042] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples in any way.

[0043] [Example 1, Comparative Example 1, Comparative Example 2] (Sample preparation) A calcined powder of the main phase containing an alkali niobate perovskite oxide and a calcined powder of the subphase were prepared.

[0044] Powders of K2CO3, Na2CO3, Nb2O5, TiO2, ZrO2, MnCO3, BaCO3, and Sc2O3 were prepared as raw materials for the main phase, and the necessary components were selected and weighed to achieve the compositions shown in Table 1. Ethanol was added to the weighed raw powders, and the mixture was wet-mixed in a ball mill using zirconia balls (3 mm diameter) for 15 hours to obtain a slurry. The resulting slurry was dried appropriately, and the resulting mixed powder was calcined in air at 900°C for 5 hours to obtain a calcined powder for the main phase.

[0045] MnCO3, TiO2, and Nb2O5 powders were prepared as raw materials for the subphase, and the necessary materials were selected and weighed. Ethanol was added to the weighed raw material powders, and the mixture was wet-mixed in a ball mill for more than 15 hours to obtain a slurry. The resulting slurry was dried appropriately, and the resulting mixed powder was calcined in an air atmosphere at a temperature of 1300°C for 5 hours to obtain a calcined powder for the subphase.

[0046] To the calcined powder of the main phase, 1.5% by volume of the calcined powder of the subphase was added, and then appropriate amounts of a dispersant, binder, and toluene were added, and the mixture was mixed in a ball mill to obtain a slurry. In this process, the subphases present in the active layer and the inactive layer were appropriately selected as shown in Table 2 to be added to the active layer and the inactive layer.

[0047] Next, a conductive paste made of Ni for the internal electrodes was applied to the ceramic green sheets using screen printing. A number of ceramic green sheets with the printed conductive paste were stacked and thermocompression bonded together so that the conductive paste was exposed alternately on both sides. The inactive layers were stacked on top of and below the laminate. Each inactive layer had a thickness of approximately 60 μm. Each active layer had a thickness of approximately 30 μm. Each internal electrode had a thickness of 2 μm. There were 31 active layers.

[0048] The obtained laminate was subjected to a binder removal treatment by holding it in a nitrogen atmosphere at a temperature condition of 300°C for 5 hours. After the binder removal treatment, the laminate was placed on an alumina setter and fired for 5 hours in a reducing atmosphere with a maximum temperature of 1000°C to 1070°C and an oxygen partial pressure of 10 atm to 12 atm. Thereafter, an annealing treatment was performed at 800°C for 10 hours in a nitrogen atmosphere. The laminates of Example 1 and the like were produced using the combinations of inactive layers and active layers shown in Table 2.

[0049] The sides of the fired laminate were cut and polished to obtain a laminate with a depth of 8 mm and a width of 8 mm. External electrodes made of Au were then formed on both sides by sputtering. A polarization treatment was then performed for 10 minutes under conditions of a DC voltage of 4 kV / mm and a temperature of 50°C to obtain a sample (piezoelectric element made of a piezoelectric ceramic laminate) such as Example 1.

[0050] [Subphase analysis] Each sample of multilayer piezoelectric ceramic element was cut at a cross section passing through the center of the top surface and parallel to the stacking direction, and the cut surface was polished. The active layer was selected at a position near the center of the cut surface and approximately equidistant from the upper and lower internal electrode layers, and the inactive layer was selected at a position near the center of the cut surface and equidistant from the edges S1 of the internal electrode and inactive layer. Analysis was then performed using an EPMA (electron probe microanalyzer). Specifically, images of the sample were taken at 5000x magnification, and elemental mapping was used to distinguish between the main phase and subphase in the active layer and inactive layer of the sample. Table 2 shows the resulting proportions (volume %) of the subphase in the active layer and inactive layer.

[0051] [Identification of the crystal structures of the main and subphases] Each sample of multilayer piezoelectric ceramic element was cut at a cross section passing through the center of the top surface and parallel to the stacking direction, and the cut surface was polished. The active layer was selected at a position near the center of the cut surface and approximately equidistant from the upper and lower internal electrode layers, while the inactive layer was selected at a position near the center of the cut surface and equidistant from the edges of the internal electrode and inactive layer. The crystal structures of the main and subphases were identified using micro-XRD. The results showed that the active layer was an MnTi2O4-based oxide, and the inactive layer was an Mn4Nb2O9-based oxide.

[0052] [Insulation resistance measurement] The insulation resistance (Ω m) of the samples in Example 1 was measured. Specifically, the samples were placed in silicone oil at 100°C, and a DC voltage of 3 kV / mm was applied for 1 minute, after which the insulation resistance (Ω m) was measured. The results are shown in Table 2.

[0053] [Strength measurement method] The three-point bending strength was measured for the samples of Example 1 and the like. During the measurement, the jig distance between the two points supporting the sample was 2 mm, and the measurement speed was 0.5 mm / min. Ten measurements were performed for one sample, and the average value was taken as the three-point bending strength (N). The results are shown in Table 2.

[0054] [Table 1]

[0055] [Table 2]

[0056] As shown in Table 2, the sample of Example 1 includes an inactive layer containing Mn4Nb2O9 as a subphase and an active layer containing Mn2TiO4 as a subphase. Both the inactive layer and the active layer contain an alkali niobate perovskite oxide as a main phase. The sample of Example 1 has a volume resistivity of 6×10 7 The sample of Example 1 had a three-point bending strength (N) of 8 N, confirming that it had high mechanical strength.

[0057] As shown in Table 2, the sample of Comparative Example 1 has an inactive layer containing Mn2TiO4 as a subphase and an active layer containing Mn2TiO4 as a subphase. That is, in the case of Comparative Example 1, both the inactive layer and the active layer contain Mn2TiO4 as a subphase. Note that both the inactive layer and the active layer contain an alkali niobate perovskite oxide as a main phase. The sample of Comparative Example 1 has a volume resistivity of 8×10 7 The sample of Comparative Example 1, however, had a three-point bending strength (N) of 3N, resulting in low mechanical strength.

[0058] As shown in Table 2, the sample of Comparative Example 2 has an inactive layer containing Mn4Nb2O9 as a subphase and an active layer containing Mn4Nb2O9 as a subphase. That is, in the case of Comparative Example 2, both the inactive layer and the active layer contain Mn4Nb2O9 as a subphase. Note that both the inactive layer and the active layer contain an alkali niobate perovskite oxide as a main phase. Such a sample of Comparative Example 2 has a volume resistivity of 8×10 6 Ω·m, which is lower than that of Example 1. Moreover, the sample of Comparative Example 2 had a three-point bending strength (N) of 7 N, which was a result of high mechanical strength. From this, it is thought that the mechanical strength can be increased by using an inactive layer containing Mn4Nb2O9, and the insulation can be increased by using an active layer containing Mn2TiO4. [Explanation of symbols]

[0059] 10... Piezoelectric ceramic laminate, 11... Ceramic layer, 11a... Active layer, 11b... Inactive layer, 12... Internal electrode, 14, 15... External electrode

Claims

1. A piezoelectric ceramic laminate in which a plurality of ceramic layers containing alkali niobate perovskite oxide as a main component and a plurality of internal electrodes are alternately stacked in one direction, The ceramic layer is formed by a portion sandwiched between the adjacent internal electrodes, and Mn ２ TiO ４ an active layer comprising: The Mn ４ Nb ２ O ９ and an inert layer comprising:

2. 2. The piezoelectric ceramic laminate according to claim 1, wherein the plurality of internal electrodes are composed mainly of Ni.

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