Ceramic Structures

Abstract

The ceramic structure comprises: a first layer having a first grain; and a second layer having a second grain located above the first layer. The first and second grains each contain: one or more metallic elements selected from Al, Si, Ti, Cr, Zr, and Y; and one or more non-metallic elements selected from N, C, and B. The first and second grains are identical compounds. If C1 is defined as the ratio of the diffraction intensity of the (002) plane of the second layer to the sum of the diffraction intensities of the (002) and (100) planes in an X-ray diffraction from the surface of the second layer, which is far from the first layer, then C1 is less than 20%.

Description

[Technical Field]

[0001] The embodiments of the invention relate to ceramic structures. [Previous Technology]

[0002] As described in Patent Document 1, a ceramic structure having a thin film formed by chemical vapor deposition (CVD) is known. Patent Document 2 describes a film formed by chemical vapor deposition that is dense, pore-free, and highly smooth. Furthermore, Patent Document 3 describes a structure with a pore content of less than 3% of the area.

[0003] Prior art documents Patent document 1: Japanese Patent Application Publication No. Sho 63-40314 Patent document 2: Japanese Patent Application Publication No. Hei 7-180057 Patent document 3: Japanese Patent Application Publication No. 2020-53579 [Summary of the Invention]

[0004] One embodiment of the ceramic structure includes: a first layer having first grains; and a second layer having second grains located above the first layer. The first grain and the second grain each contain: one or more metallic elements selected from Al, Si, Ti, Cr, Zr, and Y; and one or more non-metallic elements selected from N, C, and B. The first grain and the second grain are the same compound. If C1 is defined as the ratio of the diffraction intensity of the (002) plane of the second layer to the sum of the diffraction intensities of the (002) plane and the (100) plane in an X-ray diffraction performed from the surface of the second layer away from the first layer, then C1 is less than 20%.

Implementation Method

[0006] The above-described structure has room for further improvement in terms of enhancing the durability of ceramic structures.

[0007] Therefore, it is desirable to provide a ceramic structure with excellent durability.

[0008] Hereinafter, embodiments of the ceramic structure of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments shown below.

[0009] <Embodiment> FIG1 is a cross-sectional view showing an example of a ceramic structure according to an embodiment. In the example shown in FIG1, the ceramic structure 1 has a first layer 10 and a second layer 20. The first layer 10 has a first grain 11. The second layer 20 has a second grain 21. The first grain 11 and the second grain 21 each contain: one or more metallic elements selected from Al, Si, Ti, Cr, Zr and Y; and one or more non-metallic elements selected from N, C and B.

[0010] The first layer 10 may contain more than 50% area of ​​the first grain 11. The first layer 10 may also contain more than 80% area of ​​the first grain 11. The first layer 10 may also contain more than 90% area of ​​the first grain 11.

[0011] The second layer 20 may contain more than 50% area of ​​second grains 21. The second layer 20 may also contain more than 80% area of ​​second grains 21. The second layer 20 may also contain more than 90% area of ​​second grains 21.

[0012] Furthermore, the amount of the second grain 21 contained in the second layer 20 may be greater than the amount of the first grain 11 contained in the first layer 10. The first grain 11 and the second grain 21 are the same compound. The first grain 11 and the second grain 21 can be any one of AlN, Si3N4, SiC, TiN, TiC, ZrN, ZrB, and YN. In particular, the first grain 11 can be AlN. The same compound means, for example, if it is AlN, then Al and N are the main components, and it can be identified as AlN by XRD. For example, Al and N may not be contained in a 1:1 ratio. The Al content may be different between the first grain 11 and the second grain 21.

[0013] In X-ray diffraction of the second surface 202 of the second layer 20, which is disposed away from the first layer 10, the ratio of the diffraction intensity of the (002) surface to the sum of the diffraction intensities of the (002) surface and the (100) surface is defined as C1, and C1 is less than 20%. C1 being less than 20% means that the second layer 20 is not oriented along the C-axis. With such a structure, a second layer 20 with high hardness can be obtained, which can provide a ceramic structure 1 with excellent durability. C1 can also be less than 10%. C1 can also be less than 5%.

[0014] The diffraction intensity used to calculate C1 can be measured by the following method. The diffraction angle range (2θ): 10° to 100° can be measured using the X'Pert PRO MRD X-ray diffraction device manufactured by Spectris.

[0015] The crystal phase and diffraction intensity can be measured by the following method. Low-angle incident measurements are performed using a thin-film X-ray diffraction apparatus, the X'Pert PRO-MRD (DY1878) manufactured by PANalytical. The optical system consists of an X-ray mirror (automatic insertion attenuator, mask 5, Soller slit 0.02 rad, slit 1 / 8), a flat collimator, a CuKα tube, X-ray voltage 45 kV, 40 mA, 2θ scan range 10°–100°, incident angle 0.1°, step size 0.02°, and time 4.0 seconds / step. For example, whether the grain is AlN can be determined based on JCPDS No. 00-025-1133.

[0016] The hardness of the second layer 20 can be measured using nanoindentation. For example, it can be measured using a Bruker Japan HYSITRON TI980. The measurement temperature can be room temperature.

[0017] In the example shown in Figure 1, the first layer 10 is the substrate, for example, it may have a generally circular plate shape. In the example shown in Figure 1, the second layer 20 is located on the substrate (first layer 10), and the second layer 20 may also be in contact with the substrate (first layer 10).

[0018] The matrix (first layer 10) may contain, for example, a ceramic containing aluminum nitride (AlN) as the main component. Alternatively, the first layer 10 may also contain, for example, alumina (Al2O3) or yttrium oxide (Y2O3). Furthermore, the first layer 10 may be a sintered body obtained by firing raw material powder. When the first layer 10 is a sintered body, the first grain 11 has a high degree of crystallinity. Having such a structure provides a ceramic structure with excellent durability.

[0019] In addition, the first grain 11 and the second grain 21 can be hexagonal. In the case of hexagonal crystals, the crystallization is anisotropic, and by utilizing this anisotropy, a ceramic structure with excellent durability can be provided.

[0020] In addition, the first grain 11 and the second grain 21 can be AlN.

[0021] The second layer 20 may have a void 22 located inside the second layer 20. The void 22 may be long in the thickness direction of the second layer 20, with both ends in the thickness direction blocked. The void 22 may have at least one of a first void 22a that is connected to the first layer 10 at one end in the thickness direction and a second void 22b that is separated from the first layer 10 at one end. By having such a structure, for example, residual stress inside the second layer 20 can be reduced. Therefore, delamination and cracking between the first layer 10 and the second layer 20 are less likely to occur, and the durability of the ceramic structure 1 is improved.

[0022] The void 22 may have an elongated shape that is longer in the thickness direction than in the width direction of the second layer 20. The void 22 may be blocked at both ends in the thickness direction of the second layer 20. That is, the void 22 may be located between the first surface 201 of the second layer 20 facing the first layer 10 and the second surface 202 opposite to the first surface 201, and is not exposed on the second surface 202, which serves as the interface with the outside. Therefore, the second layer 20 has the desired durability even though it has void 22 inside. The void 22 is not a lattice defect or so-called nanopore that may exist in the second grain 21. The width of the void 22 may, for example, be 0.01 μm or more. The width of the void 22 may, for example, be 0.05 μm or more. The width of the void 22 may, for example, be 1 μm or less. The width of the void 22 may, for example, be 0.5 μm or less. The length of the void 22 may, for example, be 0.2 μm or more. The length of the pore 22 may, for example, be 0.5 μm or more. The length of the pore 22 may, for example, be 5 μm or less. The length of the pore 22 may, for example, be 1 μm or less.

[0023] The presence or absence of the gap 22 can be confirmed, for example, by observation using an electron microscope. The area percentage of the gap 22 in the second layer 20 can, for example, be 3% or more. The area percentage of the gap 22 can, for example, be 4% or more. The area percentage of the gap 22 can, for example, be 5% or less. The measurement of the area percentage of the gap 22 in the second layer 20 can, for example, be performed at the center of the cross-section of the second layer 20 after mirror finishing. The observation using an electron microscope can be performed at a magnification of 1000x to 50000x. For example, a JSM7900F electron microscope manufactured by Nippon Electronics is used, with an accelerating voltage of 5.0kV. The area percentage of the gap 22 can also be calculated using the image analysis software IMAGE Pro10 manufactured by Media Cybernetics, based on the SEM image. In this case, the SEM image is binarized using the Ward method, and the calculation is performed using the binarized image.

[0024] Additionally, the gap 22 may have a first gap 22a and a second gap 22b. The first gap 22a is a gap 22 where the lower end of one end of the second layer 20 in the thickness direction is in contact with the surface 101 of the first layer 10. The second gap 22b is a gap 22 where one end is away from the surface 101 of the first layer 10. The second layer 20 may have both the first gap 22a and the second gap 22b internally. The second layer 20 may have only either the first gap 22a or the second gap 22b.

[0025] Next, the details of the second layer 20 will be further explained with reference to Figure 2. Figure 2 is an enlarged view of region A shown in Figure 1.

[0026] The second grain 21 of the second layer 20 may have columnar crystals 21a. The columnar crystals 21a may, for example, extend along a direction intersecting the surface 101 of the first layer 10. That is, the columnar crystals 21a may extend along the thickness direction of the second layer 20. The second layer 20 may have a plurality of columnar crystals 21a arranged along the surface 101 of the first layer 10. By having columnar crystals 21a in the second grain 21, the thermal conductivity of the second layer 20 in the thickness direction is improved. Therefore, the temperature deviation in the thickness direction of the second layer 20 is reduced, and its durability is improved.

[0027] Furthermore, the width of the void 22, i.e., the length of the void 22 along the direction of the surface 101 of the first layer 10, can be smaller on the side away from the second end 222 of the first layer 10 compared to the first end 221 located in the thickness direction on the side of the first layer 10. Therefore, from the second end 222 toward the second surface 202, the void 22 is less likely to form cracks and propagate. Thus, the durability of the ceramic structure 1 containing the second layer 20 is improved. The void 22 can also be located between adjacent columnar crystals 21a. Such a void 22 can be larger or smaller than the columnar crystals 21a.

[0028] Additionally, a space 40 may be provided between the first layer 10 and the second layer 20. Here, the space 40 refers to a space extending along the surface 101 of the first layer 10. More specifically, it refers to a space whose length, in cross-section, is longer than the maximum height of the space 40 in the direction intersecting the surface 101, compared to the length of the space 40 connected by virtual line segments along the surface 101. More specifically, the length of the space 40 connected by virtual line segments along the surface 101 is at least 5 times, preferably at least 10 times, the height of the space 40 in the direction intersecting the surface 101.

[0029] In the second layer 20, the first portion, which is closer to the first layer 10, has a larger porosity than the second portion, which is further away from the first layer 10. This allows the thermal conductivity of the first portion to be lower than that of the second portion. Therefore, when the ceramic structure 1 is subjected to thermal shock from the second layer 20 side, drastic temperature changes between the first layer 10 and the second layer 20 can be suppressed. As a result, the durability of the ceramic structure 1 against thermal shock is improved. Furthermore, the first portion, for example, in the aforementioned SEM image, may include the region comprising the first surface 201, and the second portion, for example, in the aforementioned SEM image, may include the region comprising the second surface 202. Additionally, the first and second portions may partially overlap.

[0030] Figures 3 to 5 are cross-sectional views showing another example of the ceramic structure according to the embodiment. As shown in Figure 3, the second layer 20 may have a plurality of columnar crystals 21a inclined relative to the surface 101 of the first layer 10. In addition, voids 22 may be located between adjacent plurality of columnar crystals 21a. Thus, if the front end of the columnar crystal 21a is in contact with the void 22, the residual stress of the columnar crystal 21a is reduced, thereby improving the durability of the second layer 20. Also, Figure 3 illustrates a first void 22a as an example of void 22, but it may also be a second void 22b.

[0031] Furthermore, as shown in FIG4, the first layer 10 may have irregularities on its surface 101 facing the second layer 20. Additionally, the first end portion 221 of the gap 22, which is one end in the thickness direction, may be located within the recess 101b of the first layer 10. This prevents the gap 22 from expanding in the direction along the surface 101 of the first layer 10. As a result, crack formation in the columnar crystal 21a adjacent to the first end portion 221 is suppressed, and the durability of the ceramic structure 1 is improved. The same applies when the gap 22 is located on the protrusion 101a of the first layer 10. Also, FIG4 illustrates a first gap 22a as an example of the gap 22, but it could also be a second gap 22b. Furthermore, the gap 22 may also be located on the protrusion 101a of the first layer 10. In addition, Figure 4 illustrates an example of multiple columnar crystals 21a extending along the thickness direction of the second layer 20, but they may also extend obliquely from the thickness direction of the second layer 20 to correspond to the unevenness of the surface 101 of the first layer 10.

[0032] The volume resistivity of the second layer 20 at 25°C can be greater than that of the first layer 10 at 25°C. The volume resistivity of the second layer 20 at 500°C can be greater than that of the first layer 10 at 500°C. The volume resistivity of the second layer 20 at 25°C can be 1×10¹² Ω·m or higher. The volume resistivity of the second layer 20 at 500°C can be 1×10⁵ Ω·m or higher.

[0033] The volume resistivity of the second layer 20 and the first layer 10 can be measured by the three-terminal method according to JIS C 2141:1992.

[0034] The ceramic structure 1 may have a conductive layer inside. The conductive layer may function as a heater. In addition, the conductive layer may also have an adsorption function. The conductive layer may be, for example, a metal such as W, Mo, Ni, or Pt.

[0035] Additionally, as shown in FIG5, the ceramic structure 1 may further have a third layer 30 located between the first layer 10 and the second layer 20. The third layer 30 contains third grains 31 as the same compound as the second layer 20. The third layer 30 may have the third grains 31 as a main component. The third layer 30 may contain 50% or more of the third grains 31. The third layer 30 may also contain 80% or more of the third grains 31. The third layer 30 may also contain 90% or more of the third grains 31.

[0036] FIG6 is a cross-sectional view showing another example of the ceramic structure according to the embodiment. FIG7 is an enlarged view of region B shown in FIG6.

[0037] The second grains 21 of the second layer 20 may have a dendritic structure 210. The dendritic structure 210 may have stem portions 210a and dendritic portions 210b. In the stem portion 210a, for example, the second grains 21 are arranged in a direction intersecting with the surface 101 of the first layer 10 (see FIG. 6). That is, in the stem portion 210a, the second grains 21 are arranged in the thickness direction of the second layer 20. The stem portion 210a may also have the second grains 21 arranged in a direction perpendicular to the surface 101 of the first layer 10. The stem portion 210a may also include stem portions 210c in which the second grains 21 are arranged in a manner inclined from the thickness direction of the first layer 10.

[0038] The second layer 20 may have a plurality of dry portions 210a arranged along the surface 101 of the first layer 10. By having such a structure, the thermal conductivity of the second layer 20 in the thickness direction is improved. Therefore, the temperature deviation in the thickness direction in the second layer 20 is reduced, and the durability is improved.

[0039] The second layer 20 may also have dendrites 210b in which second grains 21 are arranged in a direction having a different crystal structure from the dry portion 210a. By having such a structure, for example, residual stress inside the second layer 20 can be reduced. Therefore, delamination and cracking between the first layer 10 and the second layer 20 are less likely to occur, and the durability of the ceramic structure 1 is improved.

[0040] The second layer 20 may have: a plurality of first regions 20a arranged along the surface 101 of the first layer 10; and a second region 20b located between adjacent first regions 20a. A trunk-like portion 210a may be located in the first region 20a. A plurality of branch-like portions 210b may be located in the second region 20b.

[0041] FIG8 is a cross-sectional view showing an example of a dendritic structure. The dendritic structure 210 has a trunk portion 210a and a crystal structure different from the trunk portion 210a. As shown in FIG8, the trunk portion 210a has side surfaces 23, 24 located at both ends in the width direction intersecting the length direction.

[0042] The dendritic structure 210, as a crystal structure different from the trunk portion 210a, may have dendritic portions 210b. The dendritic portions 210b may have multiple dendritic portions 210b1 located on the side 23 of the trunk portion 210a. The dendritic portions 210b may have multiple dendritic portions 210b2 located on the side 24 of the trunk portion 210a. The dendritic structure 210 may have dendritic portions 210b in which the second grains 21 are arranged at an angle θ of 30° or more and 60° or less relative to the trunk portion 210a.

[0043] The dry portion 210a can be provided in contact with the first surface 201 (see FIG6) of the second layer 20 facing the first layer 10. The dry portion 210a can be provided in contact with the second surface 202 (see FIG6) on the opposite side of the first surface 201. Alternatively, the dry portion 210a can be provided away from the first surface 201 and the second surface 202.

[0044] In addition, the branch portion 210b may be connected to the trunk portion 210a. The branch portion 210b may also be provided separately from the trunk portion 210a.

[0045] Furthermore, as shown in FIG8, the dendritic structure 210 may also have voids 25 where the stem portion 210a and the dendrite portion 210b are absent. By having such a structure, for example, the residual stress inside the second layer 20 is further reduced. Therefore, delamination and cracking between the first layer 10 and the second layer 20 are less likely to occur, and the durability of the ceramic structure 1 is improved.

[0046] Furthermore, the second layer 20 of the ceramic structure 1 may have one or both of columnar crystals 21a and dendritic structures 210 as the second grains 21.

[0047] <Method for Manufacturing Ceramic Structures> An example of a method for manufacturing ceramic structures will be described using FIG9. FIG9 is a flowchart showing an example of a method for manufacturing ceramic structures according to an embodiment.

[0048] As a substrate (first layer 10), a disk-shaped sintered body containing 90% to 99.9% by mass of AlN is prepared. Then, a second layer with AlN as the main component is formed on the surface of the substrate according to the following steps. First, a catalyst is applied to a first gas (step S11). As the first gas, a nitrogen-containing gas can be used, for example, ammonia. As the catalyst, for example, tungsten can be used. For example, if the catalyst is applied to the first gas at an environment of about 1600°C to 2200°C, the first gas is decomposed under the action of the catalyst, generating multiple active species.

[0049] Next, the active species and the second gas generated in step S11 are supplied to the first layer 10 (step S12). As the second gas, for example, trimethylaluminum can be used.

[0050] Next, a second layer 20 is formed on the first layer 10 (step S13). The first layer 10 may also be heated as needed. The temperature of the first layer 10 can be set, for example, to 420°C to 1000°C, particularly to around 600°C to 700°C. The film formation time depends on the desired thickness and can be, for example, 0.5 hours to 20 hours. In addition, the pressure during the formation of the second layer 20 (film formation pressure) can be 1 Pa to 100 Pa. For example, depending on the set temperature during film formation (film formation temperature), a ceramic structure 1 with a second layer 20 having a different crystal structure on the first layer 10 can be obtained.

[0051] An AlN sintered body containing 98% by mass of AlN crystals as the main phase was prepared in the example. This AlN sintered body was processed into a first layer with a size of 100 mm square. Furthermore, a conductive layer containing W as a metal was disposed inside the AlN sintered body. This conductive layer was formed in the shape of a heater. Then, a second layer was formed on one surface of the first layer using ammonia as the first gas, trimethylaluminum as the second gas, and tungsten as the catalyst. The film-forming temperature and film-forming pressure in step S13 are shown in Table 1. The diffraction intensities of the (002) and (100) planes of the second layer of the obtained ceramic structure are shown in Table 1. In addition, the ratio of the diffraction intensities of the (002) plane of the second layer to the sum of the diffraction intensities of the (002) and (100) planes is shown in Table 1 as C1. Empty columns or marked with "-" in the table indicate that they were not measured or calculated. In addition, the surface hardness of the second layer was measured at room temperature by nanoindentation. Hardness was measured using a Bruker Japan HYSITRON TI980. Furthermore, the indentation load of the diamond indenter was adjusted appropriately based on the thickness of the second layer.

[0052] Furthermore, the presence and shape of voids were observed using a cross-section of the second layer of the obtained ceramic structure. As a comparative example, portions equivalent to the first and second layers were fabricated using sintered bodies, and these are also recorded in Table 1. Table 1 records the film-forming temperature and the aforementioned measurements.

[0053] [Table 1]

[0054] The C1 of sample No.1 is approximately 37%. The C1 of samples No.2 to No.7 is less than 20%. There is a trend that samples with lower C1 have lower hardness. Samples No.4 and No.5 have higher hardness than sample No.1 and exhibit excellent durability.

[0055] In one embodiment, (1) the ceramic structure has: a first layer having a first grain; a second layer located above the first layer and having a second grain, the first grain and the second grain respectively containing: one or more metallic elements selected from Al, Si, Ti, Cr, Zr and Y; and one or more non-metallic elements selected from N, C and B, the first grain and the second grain being the same compound, and when C1 is defined as the ratio of the diffraction intensity of the (002) surface of the second layer to the sum of the diffraction intensities of the (002) surface and the (100) surface in an X-ray diffraction from the surface of the second layer away from the first layer, the C1 is less than 20%.

[0056] (2)In the ceramic structure of (1) above, the C1 can be less than 10%.

[0057] (3)In the ceramic structure of (1) or (2) above, the second layer has a void located inside the second layer, the void being long in the thickness direction of the second layer, both ends of the thickness direction being blocked, the void may have at least one of a first void with one end in the thickness direction connected to the first layer and a second void with one end away from the first layer.

[0058] (4)In the ceramic structure of the above (3), the porosity of the second layer in the cross section parallel to the thickness direction can be more than 3% and less than 5%.

[0059] (5)In the ceramic structure of the above (3) or (4), the second layer has a plurality of columnar crystals inclined relative to the surface of the first layer, and the voids may be located between adjacent plurality of columnar crystals.

[0060] (6)In any of the ceramic structures in (3) to (5) above, the first layer has an uneven surface on the surface facing the second layer, and one end of the void in the thickness direction may be located in the recess of the first layer.

[0061] (7)In any of the ceramic structures in (3) to (6) above, the length of the void along the direction of the surface of the first layer may be smaller than the length of the second end away from the first layer compared to the first end in the thickness direction located on the side of the first layer.

[0062] (8)In any of the ceramic structures in (3) to (7) above, the second layer may be the side of the first part that is closer to the first layer, and has a larger porosity than the second part that is further away from the first layer compared to the first part.

[0063] (9)The ceramic structure of any one of (1) to (8) above can have a conductive layer inside.

[0064] Further effects and variations can be readily derived by those skilled in the art. Therefore, the invention is presented in a broader manner, not limited to the specific details and representative embodiments described above. Thus, various modifications can be made without departing from the spirit or scope of the general concept of the invention as defined by the appended claims and their equivalents. [Simplified Explanation of the Diagram]

[0005] FIG1 is a cross-sectional view showing an example of the ceramic structure according to the embodiment. FIG2 is an enlarged view of region A shown in FIG1. ​​FIG3 is a cross-sectional view showing another example of the ceramic structure according to the embodiment. FIG4 is a cross-sectional view showing another example of the ceramic structure according to the embodiment. FIG5 is a cross-sectional view showing another example of the ceramic structure according to the embodiment. FIG6 is a cross-sectional view showing another example of the ceramic structure according to the embodiment. FIG7 is an enlarged view of region B shown in FIG6. FIG8 is a cross-sectional view showing an example of a dendritic structure. FIG9 is a flowchart showing an example of a method for manufacturing the ceramic structure according to the embodiment.

Claims

1. A ceramic structure comprising: a first layer having first grains; and a second layer having second grains located above the first layer, the first grains and the second grains respectively containing: one or more metallic elements selected from Al, Si, Ti, Cr, Zr and Y; and one or more non-metallic elements selected from N, C and B, the first grains and the second grains being the same compound, wherein, in X-ray diffraction from the surface of the second layer away from the first layer, the second layer has peaks on a (002) plane and a (100) plane, and the ratio of the diffraction intensity of the (002) plane of the second layer to the sum of the diffraction intensities of the (002) plane and the (100) plane is defined as C1, wherein C1 is less than 20%.

2. The ceramic structure as described in claim 1, wherein, The C1 level is less than 10%.

3. The ceramic structure as described in claim 1, wherein, The second layer has a void located inside the second layer, the void being elongated in the thickness direction of the second layer, both ends of the thickness direction being blocked, the void having at least one of a first void having one end in the thickness direction connected to the first layer and a second void having one end away from the first layer.

4. The ceramic structure as described in claim 3, wherein, The second layer has a porosity of more than 3% and less than 5% in a cross section parallel to the thickness direction.

5. The ceramic structure as described in claim 3 or 4, wherein, The second layer has a plurality of columnar crystals inclined relative to the surface of the first layer, and the voids are located between adjacent columnar crystals.

6. The ceramic structure as described in claim 3 or 4, wherein, The first layer has irregularities on its surface facing the second layer, and one end of the void in the thickness direction is located within the recess of the first layer.

7. The ceramic structure as described in claim 3 or 4, wherein, The length of the gap along the direction of the surface of the first layer is smaller on the side away from the second end of the first layer than on the side of the first layer in the thickness direction.

8. The ceramic structure as described in claim 3 or 4, wherein, The second layer is the side closest to the first part of the first layer, and has a larger porosity compared to the second part that is further away from the first layer than the first part.

9. The ceramic structure as claimed in any one of claims 1 to 4, wherein, It has a conductive layer inside.

Images