Piezoelectric ceramic electronic component

Abstract

The piezoelectric ceramic electronic component (10) includes: a piezoelectric ceramic unit body (1) including one or more piezoelectric ceramic layers (3a - 3h), and a plurality of electrodes (4a - 4g) provided on the surface or inside of the piezoelectric ceramic unit body (1). The piezoelectric ceramic layer (3a - 3h) is composed of a ceramic sintered body containing a sodium potassium niobate-based compound and Mn. When the piezoelectric ceramic layer C sandwiched between adjacent electrodes A and B is trisected in the thickness direction and is sequentially set as a first region R1, a second region R2, and a third region R3 from one electrode A side to the other electrode B side, the Mn concentration contained in the second region R2 is higher than the Mn concentrations contained in the first region R1 and the third region R3.

Description

Technical Field

[0001] The present invention relates to piezoelectric ceramic electronic components. Background Art

[0002] Heretofore, piezoelectric ceramic electronic components such as ultrasonic sensors, piezoelectric buzzers, and piezoelectric actuators using piezoelectric materials have been widely known. Moreover, the demand for piezoelectric ceramic electronic components that can achieve a large displacement amount even with a small voltage is increasing.

[0003] As the piezoelectric material, a lead zirconate titanate (PZT) - based compound represented by the general formula Pb(Zr,Ti)O3 has been used heretofore. In recent years, as a lead - free piezoelectric material, a potassium sodium niobate (KNN) - based compound represented by the general formula (K,Na)NbO3 has attracted attention.

[0004] In Patent Document 1, a piezoelectric ceramic electronic component is disclosed, which includes a piezoelectric ceramic unit body formed by alternately laminating and sintering internal electrodes and piezoelectric ceramic layers, and an external electrode is formed on the surface of the piezoelectric ceramic unit body. In the piezoelectric ceramic electronic component described in Patent Document 1, the internal electrode is mainly composed of Ni, and the piezoelectric ceramic layer is formed of a piezoelectric ceramic composition represented by the general formula [100{(1−x)(K 1－a－b Na a Li b )(Nb 1－c Ta c )O3−xM2M4O3}+αMn+βM4] (where x, a, b, c, α, and β are 0.005≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1, 0≤a + b≤0.9, 0≤c≤0.3, 2≤α≤15, 0.1≤β≤5.0), respectively).

[0005] In Patent Document 2, a piezoelectric ceramic electronic component in which an external electrode is formed on the surface of a piezoelectric ceramic unit body is disclosed. In the piezoelectric ceramic electronic component described in Patent Document 2, the main component of the piezoelectric ceramic unit body is formed of a niobate - based compound having a perovskite - type structure, contains Ga as a sub - component, and contains at least one of Nd and Dy, and the piezoelectric ceramic unit body is divided into a surface layer region and a region outside the surface layer region other than the surface layer region, and the total of the molar ratio of Ga to Nb (Ga / Nb), the molar ratio of Nd to Nb (Nd / Nb), and the molar ratio of Dy to Nb (Dy / Nb) in the surface layer region is more than that in the region outside the surface layer region. Further, Patent Document 2 describes that the ceramic unit body preferably contains Mn as a sub - component.

[0006] A piezoelectric thin film laminate is disclosed in Patent Document 3, which includes a first electrode layer, a first oxide layer laminated on the first electrode layer, a second oxide layer laminated on the first oxide layer, and a piezoelectric thin film laminated on the second oxide layer. In the piezoelectric thin film laminate described in Patent Document 3, it is characterized in that the resistivity of the first oxide layer is higher than that of the second oxide layer, the first oxide layer contains K, Na, and Nb, and the piezoelectric thin film contains (K, Na)NbO3.

[0007] In the piezoelectric ceramic electronic components described in Patent Documents 1 and 2, a piezoelectric ceramic layer or a piezoelectric ceramic unit body is formed by firing. On the other hand, in the piezoelectric thin film laminate described in Patent Document 3, a piezoelectric thin film is formed by a thin film forming method such as a sputtering method or a chemical vapor deposition method.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2014-139132

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-70136

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-93144 Summary of the Invention

[0013] As described in Patent Documents 1 and 2, when manufacturing a piezoelectric ceramic electronic component by alternately laminating a piezoelectric ceramic layer and a conductive layer to be an internal electrode and co-firing them, in order to prevent oxidation of Ni used as the material of the internal electrode, co-firing needs to be performed in a reducing atmosphere.

[0014] According to Patent Document 1, when firing a sodium potassium niobate-based compound as a piezoelectric material in a reducing atmosphere, it is easy to form oxygen vacancies (hereinafter referred to as oxygen defects) inside, resulting in poor sintering. Regarding this problem, Patent Documents 1 and 2 disclose that by adding Mn to the sodium potassium niobate-based compound and dissolving Mn in the sodium potassium niobate-based compound, the sinterability in a reducing atmosphere can be improved.

[0015] Furthermore, the oxygen defects formed inside the sodium potassium niobate-based compound gradually move to the negative electrode side by applying a direct current (DC) voltage or a biased alternating current (AC) voltage, so there is a risk of reducing the insulation resistance. Regarding this problem, by adding Mn to the sodium potassium niobate-based compound and dissolving Mn in the sodium potassium niobate-based compound, Mn forms an electric pair with the oxygen defects and hinders the movement of the oxygen defects, so the reduction of the insulation resistance can be suppressed.

[0016] As described above, in the piezoelectric ceramic electronic component, Mn added to the sodium potassium niobate-based compound plays an important role. Here, as shown in Patent Document 3, in the case of forming a piezoelectric thin film by a thin film forming method, the concentration of elements contained in each layer can be adjusted. On the other hand, as shown in Patent Documents 1 and 2, in the case of forming a piezoelectric ceramic layer by firing, elements such as Mn diffuse during firing, and alkali metal elements such as K and Na volatilize, so it is difficult to control the concentration of elements contained in the piezoelectric ceramic layer. Therefore, in the piezoelectric ceramic electronic component having a ceramic sintered body, it can be said that there is room for improvement in suppressing the decrease in insulation resistance.

[0017] The present invention has been made to solve the above problems, and an object thereof is to provide a piezoelectric ceramic electronic component having a piezoelectric ceramic layer composed of a ceramic sintered body and capable of suppressing a decrease in insulation resistance even during long-term driving.

[0018] The piezoelectric ceramic electronic component of the present invention includes: a piezoelectric ceramic unit body including one or more piezoelectric ceramic layers, and a plurality of electrodes provided on the surface or inside of the piezoelectric ceramic unit body. The piezoelectric ceramic layer is composed of a ceramic sintered body containing a sodium potassium niobate-based compound and Mn. When the piezoelectric ceramic layer sandwiched between adjacent electrodes is trisected in the thickness direction and is sequentially defined as a first region, a second region, and a third region from one electrode side to the other electrode side, the Mn concentration contained in the second region is higher than the Mn concentrations contained in the first region and the third region.

[0019] According to the present invention, it is possible to provide a piezoelectric ceramic electronic component having a piezoelectric ceramic layer composed of a ceramic sintered body and capable of suppressing a decrease in insulation resistance even during long-term driving. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 FIG. is a cross-sectional view schematically showing an example of a laminated piezoelectric actuator according to an embodiment of the piezoelectric ceramic electronic component of the present invention.

[0021] Figure 2 FIG. is a perspective view of a laminated piezoelectric actuator according to an embodiment of the piezoelectric ceramic electronic component of the present invention.

[0022] Figure 3 FIG. is a first schematic diagram for explaining a position for evaluating the Mn concentration contained in the piezoelectric ceramic layer.

[0023] Figure 4 FIG. is a second schematic diagram for explaining a position for evaluating the Mn concentration contained in the piezoelectric ceramic layer.

[0024] Figure 5 (a) of FIG. is an example of a mapping image of Ni element, Figure 5(b) is an example of a mapping image of the Mn element.

[0025] Figure 6 (a) of Figure 6 (b) of Figure 6 (c) of Figure 6 (d) of is a schematic diagram for explaining the steps of dividing the piezoelectric ceramic layer into a first region, a second region, and a third region.

[0026] Figure 7 (a) of Figure 7 (b) of Figure 7 (c) of is a schematic diagram for explaining the steps of D - SIMS analysis.

[0027] Figure 8 is a perspective view schematically showing a green sheet of ceramic obtained in the manufacturing process of a laminated piezoelectric actuator.

[0028] Figure 9 (a) of is a Ni mapping image, Figure 9 (b) of is a Mn mapping image, Figure 9 (c) of is a Li mapping image, Figure 9 (d) of is a coordinate diagram showing the Mn concentration distribution, Figure 9 (e) of is a coordinate diagram showing the Li concentration distribution.

[0029] Figure 10 (a) of is a Ni mapping image, Figure 10 (b) of is a Mn mapping image, Figure 10 (c) of is a Li mapping image, Figure 10 (d) of is a coordinate diagram showing the Mn concentration distribution, Figure 10 (e) of is a coordinate diagram showing the Li concentration distribution.

[0030] Figure 11 is a coordinate diagram showing the distribution of the Mn / Li concentration ratio in Specimen 3 and Specimen 6. Detailed implementation mode

[0031] Hereinafter, the piezoelectric ceramic electronic component of the present invention will be described.

[0032] However, the present invention is not limited to the following configurations, and can be appropriately changed and applied within the scope of not changing the gist of the present invention. It should be noted that a configuration obtained by combining two or more of the following described preferred configurations also belongs to the present invention.

[0033] The piezoelectric ceramic electronic component of the present invention includes: a piezoelectric ceramic unit body including one or more piezoelectric ceramic layers, and a plurality of electrodes provided on the surface or inside of the piezoelectric ceramic unit body. In the following description, the electrodes provided on the surface of the piezoelectric ceramic unit body are referred to as external electrodes, and the electrodes provided inside the piezoelectric ceramic unit body are referred to as internal electrodes.

[0034] In the embodiments shown below, the piezoelectric ceramic electronic component includes a plurality of external electrodes and a plurality of internal electrodes as electrodes. The piezoelectric ceramic electronic component of the present invention may include a plurality of internal electrodes, or may include a single layer of internal electrodes. In addition, the piezoelectric ceramic electronic component of the present invention may not include internal electrodes and only include a plurality of external electrodes. When the piezoelectric ceramic electronic component of the present invention does not include internal electrodes, the piezoelectric ceramic unit body includes a single piezoelectric ceramic layer.

[0035] [Piezoelectric Ceramic Electronic Component]

[0036] Figure 1 is a cross-sectional view schematically showing an example of a laminated piezoelectric actuator which is an embodiment of the piezoelectric ceramic electronic component of the present invention. Figure 2 is a perspective view of a laminated piezoelectric actuator which is an embodiment of the piezoelectric ceramic electronic component of the present invention. Figure 1 Corresponding to Figure 2 the cross-sectional view taken along line I-I of the shown laminated piezoelectric actuator.

[0037] Figure 1 and Figure 2 The laminated piezoelectric actuator 10 shown includes: a piezoelectric ceramic unit body 1 including piezoelectric ceramic layers 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3h, external electrodes 2a and 2b provided on the surface of the piezoelectric ceramic unit body 1, and internal electrodes 4a, 4b, 4c, 4d, 4e, 4f, and 4g provided inside the piezoelectric ceramic unit body 1. In Figure 1 and Figure 2 the external electrodes 2a and 2b are provided at both end portions of the piezoelectric ceramic unit body 1. The external electrodes 2a and 2b are made of a conductive material such as Ag, for example.

[0038] As Figure 1 shown, in the piezoelectric ceramic unit body 1, the piezoelectric ceramic layers 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3h and the internal electrodes 4a, 4b, 4c, 4d, 4e, 4f, and 4g are alternately laminated. The piezoelectric ceramic layers 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3h are made of a ceramic sintered body described later. The internal electrodes 4a, 4b, 4c, 4d, 4e, 4f, and 4g are made of a conductive material mainly composed of Ni, for example.

[0039] In the stacked piezoelectric actuator 10, one end of the internal electrodes 4a, 4c, 4e, and 4g is electrically connected to one external electrode 2a, and one end of the internal electrodes 4b, 4d, and 4f is electrically connected to the other external electrode 2b. If a voltage is applied between the external electrode 2a and the external electrode 2b, it will displace in the stacking direction indicated by the arrow Z due to the piezoelectric vertical effect.

[0040] In the piezoelectric ceramic electronic component of the present invention, the piezoelectric ceramic layer is composed of a ceramic sintered body containing a potassium sodium niobate (KNN)-based compound and Mn.

[0041] The KNN-based compound is the main component of the ceramic sintered body.

[0042] In this specification, the "main component" refers to the component with the largest proportion (mol%) in the ceramic sintered body, and preferably refers to the component with a proportion exceeding 50 mol%.

[0043] The KNN-based compound has a perovskite structure and is represented by the general formula (K, Na)NbO3. The composition of the KNN-based compound is not particularly limited. The KNN-based compound preferably contains K as an alkali metal element, and more preferably contains at least one of Na and Li in addition to K. In addition, the KNN-based compound may contain other elements in addition to the above alkali metal elements, for example, it may also contain Ta.

[0044] The ceramic sintered body preferably contains more than 50 mol% of the KNN-based compound, and more preferably contains 90 mol% or more. On the other hand, the ceramic sintered body preferably contains 99 mol% or less of the KNN-based compound, and may also contain 85 mol% or less.

[0045] Mn is a secondary component of the ceramic sintered body. As described above, Mn acts as an electric pair with oxygen defects to hinder the movement of oxygen defects and thus suppress the decrease in insulation resistance.

[0046] The ceramic sintered body preferably contains 2 mol% or more of Mn. Mn hinders the movement of oxygen defects and suppresses the decrease in insulation resistance. However, if the addition amount of Mn is large, a heterogeneous phase containing Mn will be formed in the ceramic sintered body. This heterogeneous phase does not exhibit piezoelectricity. Therefore, if the heterogeneous phase is large, the piezoelectricity of the entire ceramic sintered body will decrease. Therefore, the ceramic sintered body preferably contains 15 mol% or less of Mn, and more preferably contains 5 mol% or less.

[0047] In order to improve piezoelectric properties and the like, the ceramic sintered body may also contain other components. For example, in addition to the KNN-based compound, the ceramic sintered body may contain an appropriate amount of a compound represented by the general formula M2M4O3 (M2 represents at least one divalent element selected from Ba, Ca, and Sr, and M4 represents at least one tetravalent element selected from Zr, Sn, and Hf). Thereby, the piezoelectric properties can be further improved. In addition, the ceramic sintered body may also contain an element other than Mn as a sub-component.

[0048] The ceramic sintered body is composed of a plurality of microcrystals. The particle size of the microcrystals is preferably 10 μm or less. On the other hand, the particle size of the microcrystals is, for example, 0.1 μm or more.

[0049] The ceramic sintered body contains, for example, 90 mol% or more of (K 1－a－b Na a Li b )NbO3 (0 ≤ a ≤ 0.9, 0 ≤ b ≤ 0.1), 2 mol% to 15 mol% of Mn, and is composed of microcrystals with a particle size of 10 μm or less.

[0050] In the piezoelectric ceramic electronic component of the present invention, when the piezoelectric ceramic layer sandwiched between adjacent electrodes is trisected in the thickness direction and is sequentially set as the first region, the second region, and the third region from one electrode side to the other electrode side, the Mn concentration contained in the second region is higher than that contained in the first region and the third region.

[0051] As described above, by adding Mn to the KNN-based compound, the movement of oxygen defects contained in the piezoelectric ceramic layer can be prevented. However, the more Mn is added, the less the KNN-based compound is, and thus the piezoelectric properties are reduced. In the piezoelectric ceramic electronic component of the present invention, there is a region with a high Mn concentration in the piezoelectric ceramic layer sandwiched between adjacent electrodes. Therefore, the movement of oxygen defects contained in the piezoelectric ceramic layer can be prevented while maintaining high piezoelectric properties. In particular, since the region with a high Mn concentration exists near the center of the piezoelectric ceramic layer, the movement of oxygen defects can be effectively prevented and the reduction of the insulation resistance can be suppressed without hindering the application of an electric field to the piezoelectric ceramic layer. As a result, the insulation resistance life during DC drive can be extended.

[0052] In the piezoelectric ceramic electronic component of the present invention, the piezoelectric ceramic layer sandwiched between adjacent electrodes is, for example, the piezoelectric ceramic layer sandwiched between a set of internal electrodes adjacent in the thickness direction. The piezoelectric ceramic layer sandwiched between adjacent electrodes can be the piezoelectric ceramic layer sandwiched between a set of internal electrodes adjacent in the thickness direction and an external electrode. Alternatively, the piezoelectric ceramic layer sandwiched between adjacent electrodes can also be the piezoelectric ceramic layer sandwiched between a set of external electrodes adjacent in the thickness direction.

[0053] In this specification, the "piezoelectric ceramic layer sandwiched between a set of internal electrodes adjacent in the thickness direction" refers to the piezoelectric ceramic layer sandwiched between a pair of internal electrodes connected to different external electrodes in the piezoelectric ceramic unit body, and more specifically, the piezoelectric ceramic layer sandwiched between the pair of internal electrodes with the smallest electrode interval (hereinafter referred to as the opposed electrodes).

[0054] Figure 3 is a first schematic diagram for explaining the position for evaluating the Mn concentration contained in the piezoelectric ceramic layer.

[0055] As Figure 3 shown, when external electrodes 2a and 2b are provided at both ends of the piezoelectric ceramic unit body, the Mn concentration contained in the piezoelectric ceramic layer sandwiched between a pair of internal electrodes connected to the external electrode 2a and a pair of internal electrodes connected to the external electrode 2b, and more specifically, the pair of internal electrodes P1 with the smallest electrode interval, is evaluated. Specifically, when observed from a plane parallel to the internal electrodes, it is preferable to evaluate the Mn concentration at the centroid position of the piezoelectric ceramic unit body. On the other hand, the Mn concentration contained in the piezoelectric ceramic layer sandwiched between a pair of internal electrodes P2 both connected to the same external electrode 2a or 2b is not within the scope of evaluation.

[0056] Figure 4 is a second schematic diagram for explaining the position for evaluating the Mn concentration contained in the piezoelectric ceramic layer.

[0057] In Figure 4 , external electrodes 2a and 2b are provided at both ends of the piezoelectric ceramic unit body and external electrodes 2c are provided at both side portions of the piezoelectric ceramic unit body. In Figure 4 , the Mn concentration contained in the piezoelectric ceramic layer sandwiched between a pair of internal electrodes connected to the external electrode 2a or 2b and a pair of internal electrodes connected to the external electrode 2c, and more specifically, the pair of internal electrodes P3 with the smallest electrode interval, is evaluated. As Figure 4 shown, when the pair of internal electrodes with the smallest electrode interval does not oppose at the centroid position of the piezoelectric ceramic unit body, or when the electrode interval is not the smallest at the centroid position of the piezoelectric ceramic unit body, the position with the smallest interval of the internal electrodes can be selected in the region where the internal electrodes oppose to evaluate the Mn concentration. Similar to Figure 3 , the Mn concentration contained in the piezoelectric ceramic layer sandwiched between a pair of internal electrodes P4 both connected to the same external electrodes 2a, 2b or 2c is not within the scope of evaluation.

[0058] The distribution of the Mn concentration contained in each region of the piezoelectric ceramic layer is obtained as follows by WDX (wavelength-dispersive fluorescent X-ray). In addition, the distribution of the Mn concentration contained in each region of the piezoelectric ceramic layer is also obtained by Dynamic SIMS (D-SIMS) described later.

[0059] First, embed the piezoelectric ceramic electronic component in a resin such as polyurethane resin and grind it from the side in the stacking direction to expose the cross-section. In the obtained cross-section, adjust the field of view using WDX so that the above-mentioned opposed electrodes are included in one field of view at a magnification and the opposed electrodes are substantially parallel to the longitudinal axis of the field of view. Perform elemental mapping analysis with a metal element such as Ni, which is the main component of the internal electrode, as the target element. In addition, perform elemental mapping analysis with Mn as the target element. Regarding the width of the field of view, it is preferable that the length of one side of the field of view is 10 times or more, more preferably 20 times or more, the average particle diameter of the ceramic sintered body. This is because heterogeneous phases are likely to occur in the KNN-based compound, and when the number of particles included in one field of view is small, the distribution state of the elements cannot be correctly grasped.

[0060] Figure 5 (a) of is an example of a mapping image of Ni element, Figure 5 and (b) of

[0060] is an example of a mapping image of Mn element.

[0061] From Figure 5 the mapping image of Ni element shown in (a) of Figure 5 , it can be confirmed that the regions where Ni exists are internal electrode A and internal electrode B, and the region sandwiched between internal electrode A and internal electrode B is the piezoelectric ceramic layer C. On the other hand, from Figure 5 the mapping image of Mn element shown in (b) of Figure 5 , it can be confirmed that there is a region with a high Mn concentration near the center of the piezoelectric ceramic layer C, and it can also be confirmed that Mn exists in internal electrode A and internal electrode B.

[0062] Figure 6 (a) of Figure 6 , Figure 6 (b) of Figure 6 , Figure 6 (c) of Figure 6 and Figure 6 (d) of Figure 6 are schematic diagrams for explaining the steps of dividing the piezoelectric ceramic layer into a first region, a second region, and a third region.

[0063] From Figure 6 the detection count information obtained from the mapping image of the metal element, which is the main component of the internal electrode, shown in (a) of Figure 6 , read the peak of the detection amount of the above-mentioned metal element in the field of view. Identify the part with a detection amount of 1 / 2 or more of the obtained peak of the detection amount as the electrode part, and identify the part with a detection amount less than 1 / 2 as the ceramic part.

[0064] For Figure 6 the interfaces between internal electrode A and the piezoelectric ceramic layer C and between internal electrode B and the piezoelectric ceramic layer C shown in (a) of Figure 6 , define the boundary lines as follows.

[0065] As Figure 6 shown in (b) of Figure 6 , first, consider parallel to the longitudinal direction of the field of view from electrode A towards electrode B (in Figure 6The straight line L (horizontal in (b)). Let the interface between the internal electrode A on the straight line L and the piezoelectric ceramic layer C be Lc, and in the range from the left end to the right end of the field of view (from the upper end to the lower end in (b) of Figure 6 ), obtain the curve that forms the set of Lc. It should be noted that when there is no interface between the internal electrode A and the piezoelectric ceramic layer C on the straight line L at a certain distance from the left end of the field of view, Lc can be interrupted.

[0066] Next, as shown in (c) of Figure 6 , for the curve that forms the set of Lc, draw the straight line with the minimum sum of the squares of the longitudinal distances of the field of view from Lc. Let this straight line be the boundary line X of the interface between the internal electrode A and the piezoelectric ceramic layer C. Similarly, for the interface between the internal electrode B and the piezoelectric ceramic layer C, the boundary line Y is also set.

[0067] As shown in (d) of Figure 6 , draw the straight lines L1 and L2 that trisect the region from the boundary line X to the boundary line Y. Sequentially from the internal electrode A side to the internal electrode B side, the region between the boundary line X and the straight line L1 is set as the first region R1, the region between the straight line L1 and the straight line L2 is set as the second region R2, and the region between the straight line L2 and the boundary line Y is set as the third region R3.

[0068] For each region, calculate the Mn concentration. The calculation of the Mn concentration is to digitalize the detection amount of the fluorescent X-ray in each pixel of the mapping analysis result and find the average value in each region.

[0069] When the Mn concentration included in the first region is set as c m1 , the Mn concentration included in the second region is set as c m2 , and the Mn concentration included in the third region is set as c m3 , the value of c m2 / c m1 and the value of c m2 / c m3 can be the same or different respectively. The value of c m2 / c m1 and the value of c m2 / c m3 are respectively preferably greater than 1.0, more preferably 1.2 or more. On the other hand, the value of c m2 / c m1 and the value of c m2 / c m3 are respectively preferably 2.0 or less, more preferably 1.7 or less.

[0070] In the piezoelectric ceramic electronic component of the present invention, as shown in (c) of Figure 5As shown, the piezoelectric ceramic layer preferably sandwiched between adjacent electrodes is composed of a first low-Mn concentration layer, a high-Mn concentration layer, and a second low-Mn concentration layer in sequence from one electrode side to the other electrode side. The Mn concentration in the high-Mn concentration layer is higher than the Mn concentrations contained in the first low-Mn concentration layer and the second low-Mn concentration layer. That is, the piezoelectric ceramic layer sandwiched between adjacent electrodes preferably has a layer with a high Mn concentration sandwiched between layers with a low Mn concentration in its thickness direction. Thereby, the movement of oxygen defects is reliably prevented.

[0071] As Figure 5 shown, the high-Mn concentration layer is preferably thicker than the first low-Mn concentration layer and the second low-Mn concentration layer. The thickness of the first low-Mn concentration layer may be the same as or different from the thickness of the second low-Mn concentration layer.

[0072] In the piezoelectric ceramic electronic component of the present invention, the piezoelectric ceramic layer sandwiched between adjacent electrodes preferably contains Li. If the piezoelectric ceramic layer contains Li, the sinterability in a reducing atmosphere is improved, and the Mn concentration in the piezoelectric ceramic layer is likely to be distributed in a layered manner. As a result, the insulation resistance life during DC driving can be further extended.

[0073] From the viewpoint of improving sinterability, the Li concentration contained in the piezoelectric ceramic layer sandwiched between adjacent electrodes is preferably 0.03 wt% or more. On the other hand, if the Li concentration is increased, Li reacts with Mn and is likely to form Li x Mn2O4 (lithium manganate), so it is considered that the effect of preventing the movement of oxygen defects by Mn is not easily obtained. Therefore, the Li concentration contained in the piezoelectric ceramic layer sandwiched between adjacent electrodes is preferably 0.06 wt% or less.

[0074] In the piezoelectric ceramic layer sandwiched between adjacent electrodes, a segregation region with a Mn / Li concentration ratio of 4 or more in terms of molar ratio preferably exists. In the segregation region, the Li concentration is lower than the Mn concentration, so it is considered that the above-mentioned lithium manganate is not easily formed, and the effect of preventing the movement of oxygen defects by Mn can be fully obtained.

[0075] In the segregation region, the upper limit of the Mn / Li concentration ratio is not particularly limited, but for example, the Mn / Li concentration ratio is 15.0 or less in terms of molar ratio.

[0076] The thickness of the segregation region with a Mn / Li concentration ratio of 4 or more in terms of molar ratio is preferably 0.50 times or more, more preferably 0.55 times or more, relative to the thickness of the piezoelectric ceramic layer in which the above-mentioned segregation region exists. On the other hand, the thickness of the segregation region with a Mn / Li concentration ratio of 4 or more in terms of molar ratio is 1 time or less, preferably 0.90 times or less, more preferably 0.80 times or less, and further preferably 0.70 times or less, relative to the thickness of the piezoelectric ceramic layer in which the above-mentioned segregation region exists.

[0077] It should be noted that the existence of the segregation region is defined as follows. The piezoelectric ceramic unit is cut and polished into a cross-section parallel to the thickness direction and the long side direction, and observed in a field of view that includes the piezoelectric ceramic layer and multiple internal electrodes or external electrodes on this surface, and the internal electrodes are substantially parallel to the longitudinal axis or the transverse axis of the field of view, using a scanning electron microscope (SEM) or the like. In this field of view, the average thickness of the piezoelectric ceramic layer sandwiched between a set of internal electrodes or a set of external electrodes or a set of internal electrodes and external electrodes and not containing electrodes inside is set to t μm. Next, for a square or rectangular range with sides of 0.5t to 2t μm in both the horizontal and vertical directions, elements such as Mn, Li, and elements that are mostly contained in the electrodes and hardly contained in the ceramic part, such as Ni, are targeted, and the element distribution is mapped and analyzed for each side in the horizontal and vertical directions with a resolution of 200 pixels or more using D-SIMS, TOF-SIMS, WDX, etc. For the obtained element distribution data, first, for elements that are mostly contained in the electrodes and hardly contained in the ceramic part, the average value of the detected values in each pixel in the field of view is used as the threshold value, and the area below this value is determined as the ceramic part. Then, for Mn and Li in this field of view, for a rectangular area with a length from one end to the other end of the field of view in a direction substantially parallel to the electrode part and a width of 1 μm in a direction substantially perpendicular to the electrode part, the average amounts of Mn and Li in this rectangular area are measured in terms of the molar amount, and the area where the concentration ratio of Mn / Li is 4 or more in terms of the molar ratio is set as the segregation region.

[0078] The distributions of the Li concentration and the Mn concentration contained in the piezoelectric ceramic layer are obtained by D-SIMS as described below, for example.

[0079] Figure 7 of (a), Figure 7 of (b) and Figure 7 of (c) are schematic diagrams for explaining the steps of D-SIMS analysis. Figure 7 of (a), Figure 7 of (b) and Figure 7 of (c) represent schematic diagrams, which are different from the actual size of the sputtering region.

[0080] For Figure 7 the specimen shown in (a) of Figure 7 as shown in (b) of Figure 7 it is pre-ground to the position of the internal electrode A in front of the piezoelectric ceramic layer C to be measured. As shown in (c) of + the specimen is excavated by ion sputtering using primary ions (O2 + ions, etc.) in D-SIMS, and at the same time, secondary ions (Li 2+ions, etc.). Thus, the amount of the element contained is analyzed with respect to the processing depth by ion sputtering. The size of the sputtering area is set to 60 μm square, and the secondary ion detection target range is set to 12 μm square. It should be noted that when the distance between the internal electrodes is long (for example, 15 μm or more) and it is difficult to cut only by ion sputtering, the element can be divided into multiple single chips, polished parallel to the internal electrodes, and D-SIMS analysis is performed from the polished position. Based on the polished amount, the analysis results are combined.

[0081] (Identification of electrode part and ceramic part)

[0082] For the Ni amount detected by D-SIMS, the part up to 1 / 2 of the detection amount peak is identified as the electrode part, and the part less than 1 / 2 is identified as the ceramic part.

[0083] (Calculation of Li amount and Mn amount contained in ceramic part)

[0084] At the same time, a comparative ceramic sample with known Mn amount and Li amount is analyzed, a calibration curve is made based on the detection amount in D-SIMS, and the detection amount is corrected according to the measured value. The comparative ceramic sample is preferably a sintered body mainly composed of KNN and containing Mn and Li with a uniform composition distribution. As the comparative ceramic sample, for example, it is made into a (K 0.45 Na 0.50 Li 0.05 )(Nb 0.95 Mn 0.05 )O3 sintered body without internal electrodes, and the absolute value of the composition is evaluated in advance by ICP or the like. In addition, it is preferable to confirm that the composition distribution inside the comparative ceramic sample is small enough by analyzing the composition distribution with D-SIMS or by dividing it into small pieces and using ICP or the like.

[0085] For the comparative ceramic sample, in D-SIMS, the size of the sputtering area is set to 60 μm square, the secondary ion detection target range is set to 12 μm square, the Mn concentration and Li concentration are measured, and the value is set to a. On the other hand, the comparative ceramic sample made under the same conditions is fully dissolved with nitric acid with a concentration of 1N or more heated to 40 °C or higher, and analyzed by ICP or the like, and the value is set to b. When calculating the composition distribution of the ceramic sample to be analyzed, by multiplying the detection value x in D-SIMS by b / a, the absolute amount of the composition is calculated from the detection value in D-SIMS.

[0086] (Calculating the proportion of the segregation region where the Mn / Li concentration ratio is 4 or more in terms of molar ratio)

[0087] The molar amounts of Mn and Li are calculated from the amounts of Mn and Li obtained by the above method, and the molar ratio of Mn to Li is calculated from the obtained molar amounts. The region where the molar ratio is 4 or more is set as the segregation region, and the ratio of the thickness of the segregation region to the thickness of the piezoelectric ceramic layer in which the segregation region exists is calculated.

[0088] [Manufacturing method of piezoelectric ceramic electronic component]

[0089] Hereinafter, as an embodiment of the manufacturing method of the piezoelectric ceramic electronic component of the present invention, an example of the manufacturing method of the laminated piezoelectric actuator 10 shown in Figure 1 and Figure 2 will be described.

[0090] First, as ceramic raw materials, for example, a K compound containing K, an Nb compound containing Nb, and an Mn compound containing divalent Mn are prepared. If necessary, a Na compound containing Na, a Li compound containing Li, etc. are prepared. The form of the compound can be any one of an oxide, a carbonate, and a hydroxide.

[0091] Next, after weighing a prescribed amount of the above ceramic raw materials, these weighed materials are put into a ball mill containing a pulverization medium such as PSZ balls, and are sufficiently wet-pulverized in a solvent such as ethanol to obtain a mixture.

[0092] After drying the obtained mixture, pre-calcination and synthesis are performed at a prescribed temperature (for example, 800°C to 1000°C) to obtain a pre-calcined product.

[0093] The obtained pre-calcined product is crushed, an organic binder and a dispersant are added, and wet mixing is performed in a ball mill using pure water or the like as a solvent to obtain a ceramic slurry. Then, a ceramic green sheet is produced by performing forming processing using a doctor blade method or the like.

[0094] Then, a conductive layer having a prescribed shape is formed on the above ceramic green sheet by screen printing using a conductive paste for an internal electrode mainly composed of a conductive material such as Ni.

[0095] Figure 8 is a perspective view schematically showing a ceramic green sheet obtained in the manufacturing process of the laminated piezoelectric actuator.

[0096] As shown in Figure 8 , after laminating ceramic green sheets 6a, 6b, 6c, 6d, 6e, 6f, and 6g on which conductive layers 5a, 5b, 5c, 5d, 5e, 5f, and 5g are respectively formed, they are clamped and pressed with a ceramic green sheet 7a on which no conductive layer is formed. Thus, a ceramic laminate in which the ceramic green sheets 6a, 6b, 6c, 6d, 6e, 6f, and 6g and the conductive layers 5a, 5b, 5c, 5d, 5e, 5f, and 5g are alternately laminated is produced.

[0097] The obtained ceramic laminate is cut into a specified size and placed on an alumina firing jig. After debinding treatment is performed at a specified temperature (e.g., 250°C to 500°C), it is fired at a specified temperature (e.g., 1000°C to 1160°C) in a reducing atmosphere to form a piezoelectric ceramic unit body 1 in which internal electrodes 4a, 4b, 4c, 4d, 4e, 4f and 4g are embedded.

[0098] In order to co-fire the conductive layer composed mainly of Ni and the ceramic green sheet composed mainly of a KNN-based compound, firing is required in a reducing atmosphere. In order to make the Mn concentration in the piezoelectric ceramic layer have a layered distribution, it is important to flow in a reducing atmosphere gas sufficient for the internal volume of the firing furnace and to ensure that the fired body is fully exposed to the atmospheric gas. Therefore, it is preferred to place an insulator under the fired body to carry out firing. In addition, it is preferred to introduce a gas of 0.1a (L / min) or more relative to the internal volume a (L) of the firing furnace. It should be noted that the oxygen partial pressure of the gas is preferably maintained at the equilibrium oxygen partial pressure of Ni and NiO or a value lower than it to prevent Ni from oxidizing.

[0099] While Li addition is preferred to improve sinterability, forming the aforementioned segregation region requires reducing the Li concentration in the piezoelectric ceramic layer. Methods for adjusting the Li concentration include, for example, adjusting the amount of raw materials added during mixing of the ceramic material and adjusting the flow conditions of the reducing atmosphere gas to adjust the amount of residual Li.

[0100] Then, a conductive paste for external electrodes made of a conductive material such as Ag is applied to both ends of the piezoelectric ceramic unit 1 and baked at a predetermined temperature (eg, 750° C. to 850° C.) to form external electrodes 2 a and 2 b.

[0101] Then, a predetermined polarization treatment is performed to produce the laminated piezoelectric actuator 10. The external electrodes 2a and 2b only need to have good adhesion to the piezoelectric ceramic unit 1 and can be formed by a thin film forming method such as sputtering or vacuum deposition.

[0102] Example

[0103] The following are examples that more specifically disclose the piezoelectric ceramic electronic component of the present invention. However, the present invention is not limited to these examples.

[0104] (Sample 1)

[0105] As ceramic raw materials, potassium carbonate K2CO3, sodium carbonate Na2CO3, lithium carbonate Li2CO3, niobium oxide Nb2O5 and manganese carbonate MnCO3 were prepared. Then, the above ceramic raw materials were weighed so as to become (K 1－a－b Na aLi b )NbO3 (0≤a≤0.9, 0≤b≤0.1). Specifically, the composition is K2CO3: 15.03% by weight, Na2CO3: 13.68% by weight, Li2CO3: 1.12% by weight, Nb2O5: 67.26% by weight, and MnCO3: 2.91% by weight. The weighed materials are placed in a ball mill and mixed and stirred using ethanol as a solvent to obtain a slurry. The obtained slurry is dried and then pre-calcined at 900°C to obtain a pre-calcined powder.

[0106] The pre-calcined powder is dispersed in an organic solvent primarily composed of a binder, a dispersant, a surfactant, and ethanol to produce a slurry containing the pre-calcined raw material. The slurry containing the pre-calcined raw material is applied to a carrier film and dried to produce a ceramic green sheet containing the pre-calcined raw material.

[0107] The ceramic green sheets are cut, and a conductive layer is printed using a conductive paste for internal electrodes containing Ni as a main component. The layers are then stacked and pressure-bonded to produce a laminated and pressure-bonded body.

[0108] After the laminated pressed body is cut, it is placed on an alumina firing jig for degreasing. Then, by firing while controlling the oxygen partial pressure, a laminated sintered body containing internal electrodes with Ni as the main component is produced. It should be noted that the oxygen partial pressure is controlled so that it becomes an oxygen partial pressure lower than the equilibrium oxygen partial pressure of Ni and NiO at each temperature during firing. In addition, the firing temperature is set to 1100°C. In this embodiment, a reducing mixed gas of more than 0.1a (L / min) is introduced relative to the internal volume a (L) of the firing furnace, thereby carrying out firing. Firing is carried out by placing an insulator under the fired body so that a reducing atmosphere gas sufficient for the internal volume of the firing furnace flows in and the fired body is fully in contact with the atmosphere gas.

[0109] (Samples 2 to 4)

[0110] A laminated pressed body was produced using the same method as Sample 1. In Sample 2, the amount of Li added was changed to 0.25 times that of Sample 1, and a laminated sintered body was produced under the same conditions as Sample 1. In Sample 3, the flow rate of the atmospheric gas in Sample 2 was changed to 1.2 times that of Sample 2, and in Sample 4, the flow rate of the atmospheric gas in Sample 2 was changed to 1.4 times that of Sample 2, and a laminated sintered body was produced under the same conditions as Sample 2.

[0111] (Sample 5)

[0112] A stacked sintered body was produced by the same method as in Sample 1 except that Li was removed from the charge composition of the ceramic raw material.

[0113] (Sample 6)

[0114] A stacked laminate was fabricated in the same manner as in Specimen 1. After degreasing the stacked laminate, the gas flow rate was changed to be less than 0.1a (L / min) with respect to the internal volume a (L) of the firing furnace. Except for this, a stacked sintered body was fabricated under the same conditions as in Specimen 1. It should be noted that the oxygen partial pressure was controlled to be lower than the equilibrium oxygen partial pressure between Ni and NiO.

[0115] (Analysis of Mn concentration distribution based on WDX)

[0116] For Specimens 1 to 6, the distribution of the Mn concentration was determined by WDX according to the above method. By analyzing the elements Ni and Mn as the elements to be analyzed, an elemental mapping image was obtained. The measurement conditions of WDX are shown in Table 1. The angle of the specimen was adjusted so that the internal electrode adjacent to the observed piezoelectric ceramic layer was approximately parallel to the side of the square WDX observation field in the horizontal direction.

[0117] [Table 1]

[0118]

[0119] (Analysis of Li concentration and Mn concentration distribution based on D-SIMS)

[0120] For Specimens 1 to 6, the distribution of the Li concentration and the Mn concentration was determined by D-SIMS according to the above method. The D-SIMS analysis was performed by dividing each specimen into multiple single pieces. The measurement conditions of D-SIMS are shown in Table 2.

[0121] [Table 2]

[0122]

[0123] Figure 9 of (a), Figure 9 of (b), Figure 9 of (c), Figure 9 of (d) and Figure 9 of (e) show the analysis results of the Mn concentration and the Li concentration of Specimen 6. Figure 9 of (a) is a Ni mapping image, Figure 9 of (b) is a Mn mapping image, Figure 9 of (c) is a Li mapping image, Figure 9 of (d) is a coordinate diagram showing the Mn concentration distribution, Figure 9 of (e) is a coordinate diagram showing the Li concentration distribution.

[0124] Figure 10 of (a), Figure 10 of (b), Figure 10 of (c), Figure 10 of (d) and Figure 10(e) shows the analysis results of the Mn concentration and Li concentration of Specimen 3. Figure 10 (a) is the Ni mapping image, Figure 10 (b) is the Mn mapping image, Figure 10 (c) is the Li mapping image, Figure 10 (d) is the coordinate graph showing the Mn concentration distribution, ​ (e) is the coordinate graph showing the Li concentration distribution.

[0125] In ​ (a) to ​ (e) and ​ (a) to ​ (e), the results up to 15 μm are shown. This is the depth at which correct D-SIMS analysis can be performed. It should be noted that the position of the 15-μm analysis depth corresponds to the second region of the piezoelectric ceramic layer. Specifically, it is located between the straight line L1 and the straight line L2 shown in ​ (d).

[0126] ​ is the coordinate graph showing the distribution of the Mn / Li concentration ratio in Specimen 3 and Specimen 6.

[0127] From ​ it can be confirmed that there is a segregation region in Specimen 3 where the Mn / Li concentration ratio is 4 or more in terms of molar ratio.

[0128] For Specimens 1 to 6, Table 3 shows the values of c m1 when the Mn concentration contained in the first region of the piezoelectric ceramic layer is set to c m2 , the Mn concentration contained in the second region is set to c m3 , and the Mn concentration contained in the third region is set to c m2 / c m1 and the values of c m2 / c m3 . Table 3 also shows the Li concentration contained in the piezoelectric ceramic layer and the ratio of the thickness of the segregation region to the thickness of the piezoelectric ceramic layer when the region where the Mn / Li concentration ratio in the piezoelectric ceramic layer is 4 or more in terms of molar ratio is set as the segregation region.

[0129] It should be noted that the Mn concentration and Li concentration contained in each region are obtained as follows. First, the weight fraction of Mn contained in the standard sample is measured by ICP, and this concentration is set to c standard . On the other hand, the average detection value of Mn when measuring the standard sample by TOF-SIMS is set to I standard . When the detection value of Mn when measuring the device to be measured by TOF-SIMS is set to I sample , with c m = cstandard ×I sample / I standard Find the concentration c of Mn in this region in the form of m .

[0130] In addition, for Samples 1 to 6, the insulation resistivity ρ (Ω·cm) when applying a DC electric field of 3.8 kV / mm at 100°C was measured, and the time until it decreased to logρ ≤ 5 was defined as the DC load life. Table 3 shows the relative values with the DC load life of Sample 6 set to 1. Furthermore, the densities of Samples 1 to 6 are shown in Table 3.

[0131] [Table 3]

[0132]

[0133] In Table 3, those marked with * in the sample numbers are comparative examples outside the scope of the present invention.

[0134] As shown in Samples 1 to 5, by providing a region with a high Mn concentration near the center of the piezoelectric ceramic layer, the life during DC driving is extended compared to Sample 6. This is considered to be because the movement of oxygen defects can be prevented by the region with a high Mn concentration.

[0135] As shown in Samples 1 to 4, if Li is contained in the piezoelectric ceramic layer, the sintered density is higher and the life during DC driving is extended compared to Sample 5. It is considered that if Li is contained in the piezoelectric ceramic layer, Li can move together with Mn during the sintering process, so it is easy to form a layered region with different Mn concentrations in the piezoelectric ceramic layer.

[0136] As shown in Samples 2 to 4, if the Li concentration contained in the piezoelectric ceramic layer is 0.03 wt% to 0.06 wt% or less, the life during DC driving is further extended. This is considered to be because a large amount of Mn remains in the piezoelectric ceramic layer.

[0137] As shown in Samples 3 and 4, if the proportion of the segregation region where the Mn / Li concentration ratio is 4 or more in terms of molar ratio is large, the life during DC driving is significantly extended. If the proportion of the segregation region is large, it is considered that since the formation of a stable compound between Li and Mn is hindered, the amount of Mn dissolved in the KNN-based compound can be increased.

[0138] On the other hand, in Sample 6, the life during DC driving is short. This is considered to be because the Mn concentration does not form a layered structure within the piezoelectric ceramic layer, and the movement of oxygen defects cannot be sufficiently prevented.

[0139] Symbol Explanation

[0140] 1 Piezoelectric ceramic unit

[0141] 2a, 2b, 2c External electrode

[0142] Piezoelectric ceramic layers 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h

[0143] Internal electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g

[0144] Conductive layers 5a, 5b, 5c, 5d, 5e, 5f, 5g

[0145] Green ceramic sheets 6a, 6b, 6c, 6d, 6e, 6f, 6g, 7a

[0146] 10-layer stacked piezoelectric actuator (piezoelectric ceramic electronic component)

[0147] Internal electrodes A, B

[0148] Piezoelectric ceramic layer C

[0149] A pair of internal electrodes P1, P2, P3, P4

[0150] First region R1

[0151] Second region R2

[0152] Third region R3

Claims

1. A piezoelectric ceramic electronic component, comprising: A piezoelectric ceramic unit body including a plurality of piezoelectric ceramic layers, and A plurality of internal electrodes provided inside the piezoelectric ceramic unit body; The piezoelectric ceramic layer is composed of a ceramic sintered body containing a sodium potassium niobate-based compound and Mn, When the piezoelectric ceramic layer sandwiched between adjacent electrodes is trisected in the thickness direction and sequentially set as a first region, a second region, and a third region from one electrode side to the other electrode side, the Mn concentration contained in the second region is higher than the Mn concentrations contained in the first region and the third region, The piezoelectric ceramic layer sandwiched between adjacent electrodes is a piezoelectric ceramic layer sandwiched between a set of the internal electrodes adjacent in the thickness direction.

2. A piezoelectric ceramic electronic component, comprising: A piezoelectric ceramic unit body including a plurality of piezoelectric ceramic layers, and A plurality of external electrodes provided on the surface of the piezoelectric ceramic unit body and one or more internal electrodes provided inside the piezoelectric ceramic unit body; The piezoelectric ceramic layer is composed of a ceramic sintered body containing a sodium potassium niobate-based compound and Mn, When the piezoelectric ceramic layer sandwiched between adjacent electrodes is trisected in the thickness direction and sequentially set as a first region, a second region, and a third region from one electrode side to the other electrode side, the Mn concentration contained in the second region is higher than the Mn concentrations contained in the first region and the third region, The piezoelectric ceramic layer sandwiched between adjacent electrodes is a piezoelectric ceramic layer sandwiched between a set of the internal electrodes adjacent in the thickness direction and an external electrode.

3. A piezoelectric ceramic electronic component, comprising: A piezoelectric ceramic unit body including one or more piezoelectric ceramic layers, and A plurality of external electrodes provided on the surface of the piezoelectric ceramic unit body; The piezoelectric ceramic layer is composed of a ceramic sintered body containing a sodium potassium niobate-based compound and Mn, When the piezoelectric ceramic layer sandwiched between adjacent electrodes is trisected in the thickness direction and sequentially set as a first region, a second region, and a third region from one electrode side to the other electrode side, the Mn concentration contained in the second region is higher than the Mn concentrations contained in the first region and the third region, The piezoelectric ceramic layer sandwiched between adjacent electrodes is a piezoelectric ceramic layer sandwiched between a set of the external electrodes adjacent in the thickness direction.

4. The piezoelectric ceramic electronic component according to any one of claims 1 to 3, wherein, The piezoelectric ceramic layer sandwiched between adjacent electrodes is sequentially composed of a first Mn low-concentration layer, a Mn high-concentration layer, and a second Mn low-concentration layer from one electrode side to the other electrode side, The Mn concentration contained in the Mn high-concentration layer is higher than the Mn concentrations contained in the first Mn low-concentration layer and the second Mn low-concentration layer.

5. The piezoelectric ceramic electronic component according to any one of claims 1 to 3, wherein, The piezoelectric ceramic layer sandwiched between adjacent electrodes contains Li.

6. The piezoelectric ceramic electronic component according to claim 5, wherein, The Li concentration contained in the piezoelectric ceramic layer sandwiched between adjacent electrodes is 0.03 wt% to 0.06 wt%.

7. The piezoelectric ceramic electronic component according to claim 5, wherein, In the piezoelectric ceramic layer sandwiched between adjacent electrodes, there is a segregation region where the Mn / Li concentration ratio is 4 or more in terms of molar ratio, The thickness of the segregation region is 0.50 times or more relative to the thickness of the piezoelectric ceramic layer in which the segregation region exists.

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