Laminate

Abstract

This multilayer body (10) is provided with a substrate (11) and an oxide site (13) that is positioned on the substrate (11). The oxide that constitutes the oxide site (13) has an apatite-type crystal structure which contains at least two rare earth elements, silicon and oxygen, wherein with respect to the X-ray diffraction pattern thereof, a diffraction peak assigned to the (004) plane is observed at the position of 2θ = 51.9° ± 0.9°. The ratio of the linear expansion coefficient of the oxide in the a-axis direction to the linear expansion coefficient of the substrate (11) is 0.15 to 1.45.

Description

[Technical Field]

[0001] The present invention relates to a laminate having an oxide portion and a substrate. The laminate of the present invention is suitably used, for example, as various sensors. [Background technology]

[0002] Oxide ion conductors are used in a variety of electrochemical devices, such as solid electrolytes in various batteries including solid electrolyte fuel cells, ion batteries, and air batteries, as well as gas separation membranes in gas sensors. For example, Patent Document 1 describes the use of oriented apatite-type oxide ion conductors as solid electrolyte fuel cells and oxygen sensors. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 183068 [Overview of the Initiative]

[0004] When using a solid electrolyte, a thin film of the solid electrolyte is often placed on a substrate that is inert to electrochemical reactions to form a laminate. In this case, reducing the thickness of the solid electrolyte has the effect of lowering its electrical resistance. Incidentally, in order to achieve sufficient ionic conductivity in a solid electrolyte, it is sometimes heated. In this case, when the solid electrolyte constitutes part of the laminate described above, cracks may occur between the substrate and the solid electrolyte in the laminate due to differences in thermal expansion. The occurrence of cracks is one of the causes of a significant decrease in the performance and reliability of electrochemical devices made of laminates containing solid electrolytes.

[0005] Therefore, the object of the present invention is to provide a laminate that exhibits ionic conductivity while being less susceptible to damage such as cracks.

[0006] The present invention relates to a laminate comprising a substrate and oxide portions located on the substrate, The oxide constituting the oxide portion contains at least two rare earth elements, silicon, and oxygen, and in the X-ray diffraction pattern, a diffraction peak originating from the (004) plane is observed at the position 2θ = 51.9° ± 0.9°, and has an apatite-type crystal structure. The present invention provides a laminate in which the ratio of the linear expansion coefficient of the oxide in the a-axis direction to the linear expansion coefficient of the substrate is 0.15 or more and 1.45 or less. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic cross-sectional view in the thickness direction showing the structure of one embodiment of the laminate of the present invention. [Modes for carrying out the invention]

[0008] The present invention will be described below based on its preferred embodiments. The present invention relates to a laminate having a laminated structure comprising a substrate and oxide portions. In the laminate of the present invention, the oxide portions are arranged on the substrate. In one embodiment of the present invention, the oxide portions are arranged on the substrate so as to be in direct contact with the substrate. In another embodiment of the present invention, the oxide portions are arranged indirectly on the substrate via one or more portions different from the oxide portions. Typical examples of portions different from the oxide portions include the native oxide film on the surface of the silicon substrate and electrodes (see Figure 1), which will be described later.

[0009] There are no particular restrictions on the shape of the substrate and oxide portion, and various shapes can be adopted depending on the specific application of the laminate of the present invention. For example, a plate-like body having two opposing main surfaces can be used as the substrate. If the substrate is a plate-like body, there are no particular restrictions on its shape in plan view, and it can be any shape such as a polygon such as a rectangle, or a circle or an ellipse.

[0010] When using a plate-like body as a substrate, the oxide site can be disposed on at least one of the two main surfaces. When the oxide site is disposed on the main surface, the contour of the main surface in plan view can be made the same as the contour of the oxide site. Alternatively, in plan view, the oxide site can also be disposed on the main surface such that the contour of the main surface of the substrate is located outside the contour of the oxide site.

[0011] The substrate is solely used as a support for the oxide site. For this purpose, it is advantageous for the substrate to have a higher strength than the oxide site. Also, it is advantageous for the substrate to have a property that does not inhibit the function of the oxide site. As will be described later, when the oxide site has oxide ion conductivity, the substrate is preferably composed of a material that is inert to oxide ion conductivity.

[0012] As shown in FIG. 1 to be described later, through-holes extending in the thickness direction may be formed in the substrate. Since it is generally convenient to use dry etching or wet etching for forming the through-holes, it is advantageous for the material constituting the substrate to be suitable for these etching methods. From this viewpoint, the substrate includes, for example, materials containing silicon (such as single crystalline silicon and silicon compounds (such as quartz and glass)), semiconductors such as gallium arsenide, metals such as aluminum, copper, nickel and their alloys, and ceramics such as strontium titanate and magnesia. Among these materials, it is particularly preferable to use a material containing silicon in terms of mass productivity and etching.

[0013] Next, the oxide site disposed on the substrate will be described. The oxide site is preferably composed of a solid electrolyte material of an oxide having oxide ion conductivity. From the viewpoint of expressing oxide ion conductivity in the oxide site, the oxide constituting the oxide site is preferably composed of a material containing at least two or more rare earth elements, silicon, and oxygen. Such materials are generally substances in the category called rare earth silicates.

[0014] Examples of the rare earth elements include one or more elements selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. In addition, the oxide constituting the oxide moiety may contain at least two or more rare earth elements, silicon, and oxygen, as well as one or more elements selected from the group consisting of, for example, Be, Mg, Ca, Sr, and Ba.

[0015] The oxide constituting the oxide portion preferably has an apatite-type crystal structure. In particular, the oxide preferably has an oriented apatite-type crystal structure. "Oriented" means that the crystal has an orientation axis. It is especially preferable that the oxide has c-axis orientation.

[0016] When the oxide constituting the oxide portion is measured by an X-ray diffraction (hereinafter also referred to as "XRD") apparatus, characteristic diffraction peaks are observed on the (002) plane, (004) plane, (006) plane, etc. In particular, the oxide is characterized by the diffraction angle (2θ) at which the diffraction peak originating from the (004) plane is observed, compared to lanthanum silicate known to date. Specifically, in the XRD pattern measured by a powder XRD apparatus using CuKα rays, the oxide preferably shows a diffraction peak originating from the (004) plane (hereinafter referred to as the "004 diffraction peak"; similarly, the diffraction peak originating from the (002) plane and the diffraction peak originating from the (006) plane are referred to as the "002 diffraction peak" and the "006 diffraction peak," respectively) at a position of 2θ = 51.9° ± 0.9°, and it is particularly preferable that the 004 diffraction peak is observed at a position of 2θ = 51.9° ± 0.7°, and even more preferably at a position of 51.9° ± 0.6°. Even when multiple peaks are observed within 51.9°±0.9°, the 004 diffraction peak can be identified from the X-ray diffraction pattern. The observation of the 004 diffraction peak at 2θ=51.9°±0.9° in the oxide constituting the oxide region indicates that the oxide is crystallized, and therefore possesses high ionic conductivity.

[0017] Furthermore, in addition to the 004 diffraction peak, peaks originating from the (00l) plane (where l is a positive integer), such as the 002 diffraction peak and the 006 diffraction peak, are also observed in the oxide constituting the oxide region. The positions of these diffraction peaks are shifted to higher angles, unlike those of lanthanum silicate known to date. Even if the oxide constituting the oxide region does not have c-axis orientation, the (00l) plane can be identified from the X-ray diffraction pattern.

[0018] The inventors' research has revealed that adjusting the composition of the oxide is effective in causing the oxide constituting the oxide moiety to exhibit a 004 diffraction peak at the aforementioned position. As described above, the oxide ion conductor of the present invention preferably contains at least two rare earth elements, silicon (Si), and oxygen (O), and more preferably contains lanthanum group elements and at least one of yttrium and scandium as rare earth elements. Furthermore, it is particularly preferable that the oxide constituting the oxide moiety contains at least lanthanum (La) and yttrium (Y).

[0019] The oxides particularly preferred in the present invention are those of formula (1):A 9.3+x-a Y a [Si 6.0-y M y ]O 26.0+z It is represented as follows. In formula (1), A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba, and includes at least La. M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Ge, Zr, Ta, Nb, B, Zn, Sn, W, and Mo. x is a number between -1.4 and 1.5 (inclusive). y is a number between 0.0 and 3.0 (inclusive). z is a number between -5.0 and 5.2 (inclusive). a is a number between 0.1 and 10.4 (inclusive). The ratio of moles of A to moles of Si is between 1.4 and 3.7.

[0020] In formula (1), among the elements listed as A, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba are all elements that have the common characteristic of being lanthanides or group 2 elements that can form positively charged ions and constitute an apatite-type hexagonal crystal structure. Among these, from the viewpoint of further increasing the oxide ion conductivity of the oxide moiety, it is preferable that A is one or more elements selected from the group consisting of La, Nd, Ba, Sr, Ca, and Ce, and that it contains at least La.

[0021] In formula (1), the M element is preferably one or more selected from the group consisting of B, Ge, Zn, W, Sn, and Mo. In particular, it is even more preferable that the M element is one or more selected from the group consisting of B, Ge, and Zn, in terms of high orientation and high productivity of the oxide constituting the oxide moiety.

[0022] In formula (1), x is preferably -1.0 to 1.0, and more preferably 0.0 to 0.7, and more preferably 0.4 to 0.7, from the viewpoint of improving the degree of orientation of the oxide constituting the oxide site and the oxide ion conductivity.

[0023] In formula (1), y is preferably 0.4 or more and less than 1.0, more preferably 0.4 or more and 0.9 or less, more preferably 0.8 or less, particularly 0.7 or less, and especially preferably 0.5 or more and 0.7 or less, from the viewpoint of filling the positions of Si elements in the apatite-type crystal lattice.

[0024] In formula (1), z is preferably between -5.0 and 3.7, more preferably between -3.0 and 2.0, and more preferably between -2.0 and 1.5, and even more preferably between -1.0 and 1.0, from the viewpoint of maintaining electrical neutrality within the apatite crystal lattice.

[0025] In formula (1), the ratio of the number of moles of A to the number of moles of Si, in other words, (9.3 + x - a) / (6.0 - y) in formula (1), is preferably 1.4 or more and 3.0 or less, and more preferably 1.5 or more and 2.0 or less, from the viewpoint of maintaining the spatial occupancy rate in the apatite-type crystal lattice.

[0026] Specific examples of the oxide represented by formula (1) include La 8.6 Y 1.1 (Si 5.3 B 0.7 )O 26.7 , La 8.0 Y 1.7 (Si 5.3 B 0.7 )O 26.7 , La 7.5 Y 2.2 (Si 5.3 B 0.7 )O 26.7 and the like, but are not limited thereto.

[0027] In a preferred embodiment, the oxide constituting the oxide site can have an orientation degree measured by the Lotgering method, that is, a Lot of 0.6 or more, and particularly 0.8 or more, and especially 0.9 or more. In order to make the Lotgering orientation degree 0.6 or more, for example, it can be produced according to the method described in International Publication No. 2017 / 018149.

[0028] In a preferred embodiment, the oxide constituting the oxide site has an oxide ion conductivity of 10 -9 S / cm or more at 600 °C, and particularly 10 -8 S / cm or more, and especially 10 -7 S / cm or more. In order to make the oxide ion conductivity 10 -7 S / cm or more at 600 °C, it is preferable to make the above-described Lotgering orientation degree 0.6 or more. However, it is not limited to such a method.

[0029] In the laminate of the present invention, the coefficient of linear expansion between the oxide portion and the substrate is controlled. Specifically, the coefficient of linear expansion of the substrate is controlled. S The linear expansion coefficient (CT) in the a-axis direction of the oxide constituting the oxide site. E The ratio (i.e., CT) E / CT S The thermal expansion ratio (hereinafter also referred to as the "thermal expansion ratio") is controlled to be between 0.15 and 1.45. By controlling the linear expansion coefficient in this way, even when the laminate of the present invention is heated and cooled, cracks caused by differences in thermal expansion between the substrate and the oxide portion are effectively suppressed in the oxide portion. From the viewpoint of making this advantage even more pronounced, the thermal expansion ratio is preferably between 0.25 and 1.10, and more preferably between 0.6 and 0.95. Furthermore, even if other parts, such as electrodes, are placed between the substrate and the oxide portion, the difference in thermal expansion between the substrate and the oxide portion becomes a problem because the electrode thickness is generally small. Coefficient of thermal expansion of the substrate CT S , and the coefficient of linear expansion CT in the a-axis direction of the oxide constituting the oxide site E The measurement method will be explained in the examples described later. Linear expansion coefficient CT S CT E This measurement can be performed on the substrate or the oxide itself that constitutes the oxide portion before manufacturing the laminate of the present invention. Alternatively, the coefficient of linear expansion CT can be measured on the powder of the material constituting the substrate or the powder of the oxide portion constituting the oxide portion, and the coefficient of linear expansion CT can be measured on the said powder. S CT E This allows for the measurement of [specific parameters]. The substrate may be single crystal or polycrystalline. In the case of a single crystal, it may be oriented or not. There are no particular restrictions on the thickness of the substrate, but it is typically 10 μm to 1000 μm, preferably 100 μm to 650 μm, and more preferably 250 μm to 350 μm.

[0030] When the oxide constituting the oxide moiety is represented by formula (1) above, it is advantageous for the oxide to have a space group P63 / m in order to control the coefficient of linear expansion of the oxide moiety, thereby making it less likely for cracks to occur in the oxide moiety. From the viewpoint of making this advantage even more pronounced, it is preferable that A in formula (1) contains at least La. There are two crystallographically distinct sites (Wyckoff symbols 4f and 6h) occupied by La atoms, and it is particularly preferable that there are more Y atoms at the 4f site than at the Wyckoff position 6h site among the sites occupied by La atoms. In order for the oxide constituting the oxide moiety to have such a crystal structure, the oxide moiety containing Y should be fired in a temperature range in which an apatite-type crystal structure can be formed. The Rietveld method is used to determine which atomic site the Y atom is coordinated to. The detailed procedure will be explained in the examples below.

[0031] When the substrate contains silicon, a thermal expansion ratio of 0.15 to 1.45 is preferable from the viewpoint that crack formation in the oxide portion is effectively suppressed. From this viewpoint, when the substrate contains silicon, a thermal expansion ratio of 0.45 to 1.35 is more preferable, and 0.65 to 1.25 is even more preferable. Examples of silicon-containing substrates include silicon oxide, quartz, and at least one of crystalline silicon. When forming through holes in the substrate, it is preferable that the substrate contains crystalline silicon from the viewpoint of good etching performance.

[0032] Figure 1 shows a schematic cross-sectional view in the thickness direction illustrating one embodiment of the laminate of the present invention. The laminate 10 shown in the figure is constructed by stacking a first electrode layer 12 and an oxide portion 13 in that order on one surface of a substrate 11.

[0033] A preferred method for manufacturing the laminate 10 of the embodiment shown in Figure 1 is as follows. The manufacturing of the laminate 10 includes the formation of oxide portions 13, the formation of a first electrode layer 12 which is performed before the formation of the oxide portions 13 if necessary, and the formation of a second electrode layer which is performed after the formation of the oxide portions 13 if necessary. Each of these steps will be described below.

[0034] First, a substrate 11 is prepared, and an oxide portion 13 is formed on one surface of the substrate 11. Various thin-film formation methods are used to form the oxide portion 13. Specifically, the oxide portion 13 can be formed by physical vapor deposition (PVD) methods such as evaporation, sputtering, and ion plating, or by chemical vapor deposition (CVD). Of these various methods, sputtering is preferred because it allows for the uniform deposition of the oxide portion 13 on the substrate 11 and offers excellent mass productivity.

[0035] When forming the first electrode layer 12, the first electrode layer 12 formation process is carried out before the formation of the oxide portion 13. The first electrode layer 12 is formed on the side of the substrate 11 where the oxide portion 13 is formed. Similar to the formation of the oxide portion 13, various thin-film formation methods can be used for forming the first electrode layer 12. Specifically, the first electrode layer 12 can be formed by physical vapor deposition (PVD) methods such as evaporation, sputtering, and ion plating, or by chemical vapor deposition (CVD) methods. The sputtering method is preferred because it allows for easy formation of a first electrode layer 12 with the desired composition and offers excellent mass-productivity.

[0036] Various materials can be used as the constituent material for the first electrode layer 12. If the constituent material is a cermet or the like, the firing process of the first electrode layer 12 and the subsequent process of forming the holes 14 in the substrate 11 may be performed after the formation of the first electrode layer 12 and before the formation of the oxide portion 13. When the constituent material of the first electrode layer 12 is, for example, cermet, the firing process of the first electrode layer 12 is performed to reliably create a sintered structure in the first electrode layer 12 in which an ion-conducting metal oxide such as samarium-doped cerium oxide (hereinafter also referred to as "SDC") is bonded by platinum or the like, i.e., cermet. From the viewpoint of reliably forming the aforementioned sintered structure, the firing temperature is preferably 300°C to 1400°C, more preferably 500°C to 1200°C, and even more preferably 600°C to 1100°C. From a similar viewpoint, the firing time in the firing process is preferably 1 minute or more and 20 hours or less, more preferably 10 minutes or more and 15 hours or less, even more preferably 30 minutes or more and 10 hours or less, and most preferably 1 hour or more and 5 hours or less. The firing atmosphere during the firing process is not specified and may be either an oxygen-containing atmosphere or a reducing atmosphere. By performing the firing process of the first electrode layer 12, if the electrode layer is a layer containing, for example, SDC and platinum, a layer consisting only of SDC is formed on the surface of the substrate 11 facing the electrode layer. Alternatively, if the substrate 11 is made of silicon, an SiO2 layer is formed on the surface of the substrate 11 facing the electrode layer.

[0037] In the step of forming the oxide portion 13, the oxide portion 13 having the desired composition can be formed by using a target with the desired composition. After the oxide portion is formed, firing is performed. The firing temperature should be a temperature at which sufficient crystallization occurs, preferably 300°C to 1300°C, more preferably 500°C to 1200°C, and even more preferably 600°C to 1100°C. The firing time should be preferably 1 minute to 10 hours, more preferably 10 minutes to 5 hours, and even more preferably 30 minutes to 3 hours. The firing atmosphere in the firing process is not specified and may be an oxygen-containing atmosphere or a reducing atmosphere. By going through such a firing process, the crystallinity of the oxide portion 13 is increased, and high conductivity can be obtained.

[0038] Returning to Figure 1, the substrate 11 is a plate-like body having two opposing main surfaces 11a and 11b. Multiple holes 14 are formed in the substrate 11. The holes 14 extend along a direction intersecting the surface of the substrate 11 facing the first electrode layer 12, that is, the main surface 11a shown in Figure 1. Generally, the holes 14 extend along a direction perpendicular to the surface of the substrate 11 facing the first electrode layer 12. The holes 14 extend to penetrate between the two main surfaces 11a and 11b of the substrate 11 and open at each of the main surfaces 11a and 11b. In other words, the holes 14 are through holes. The holes 14 are formed to improve gas supply, such as the supply of oxygen gas to the first electrode layer 12, when an electrochemical element comprising a laminate 10 is used.

[0039] The hole 14 is open on the main surface 11b. The shape of the hole 14 opening on the main surface 11b may be, for example, circular. However, the shape of the hole 14 is not limited to this, and may be other shapes, such as polygons like triangles or quadrilaterals, or ellipses, or combinations thereof. It is particularly preferable that it be circular or a regular polygon.

[0040] The holes 14 may be formed over the entire area of ​​the opposing region between the substrate 11 and the first electrode layer 12, or they may be formed in at least a part of the opposing region. In the embodiment shown in Figure 1, the holes 14 are formed in the inner region 11d of the opposing region between the substrate 11 and the first electrode layer 12, which is located inward from the peripheral region 11c of the substrate 11.

[0041] The holes 14 opening in the main surface 11b can be arranged regularly or irregularly. There are no particular restrictions on the arrangement pattern of the holes 14, and various arrangement patterns can be adopted as long as gas can be supplied smoothly to the first electrode layer 12 through the holes 14.

[0042] The hole 14 extends linearly between the two main surfaces 11a and 11b of the substrate 11. The cross-sectional shape of the hole 14 is the same at any position between the two main surfaces 11a and 11b of the substrate 11. For example, if the cross-sectional shape of the hole 14 is circular, the hole 14 may be a cylindrical space. Alternatively, the cross-sectional shape of the hole 14 can be made different depending on its position between the two main surfaces 11a and 11b of the substrate 11. For example, the opening area on the exposed surface of the substrate 11 (i.e., main surface 11b) can be made larger than the opening area on the surface facing the first electrode layer 12 (i.e., main surface 11a) of the substrate 11. For example, the hole 14 can be a space with the shape of a frustocone.

[0043] In the manufacturing of the laminate 10 shown in Figure 1, the hole formation step 14 can also be performed after the formation of the oxide portion 13. In this case, it is not necessary to perform the hole formation step of the substrate 11 after the completion of the first electrode layer 12 formation step and before the formation step of the oxide portion 13.

[0044] The substrate 11 is preferably 10 μm or more and 1000 μm or less in thickness, more preferably 100 μm or more and 650 μm or less, and even more preferably 250 μm or more and 350 μm or less. By setting the thickness of the substrate 11 within this range, the substrate 11 functions sufficiently as a support for the first electrode layer 12, the oxide portion 13, and the second electrode layer described later. The thickness of the substrate 11 can be measured, for example, with a caliper or a digital thickness measuring instrument.

[0045] In the laminate 10 shown in Figure 1, oxide portions 13 are arranged on the substrate 11 via a first electrode layer 12. The oxide portions 13 generally have a certain thickness. Details of the oxides constituting the oxide portions 13 are as described above. The thickness of the oxide portion 13 is preferably 10 nm to 1000 nm, more preferably 30 nm to 500 nm, and even more preferably 50 nm to 300 nm, from the viewpoint of effectively reducing the electrical resistance of the laminate 10. The thickness of the oxide portion 13 can be measured by cross-sectional observation using a stylus-type step meter or an electron microscope.

[0046] In the laminate 10 shown in Figure 1, a first electrode layer 12 is positioned between the substrate 11 and the oxide portion 13. The first electrode layer 12 functions as an electrode for the oxide portion 13. The material constituting the first electrode layer 12 can be selected appropriately depending on the type of oxide constituting the oxide portion 13.

[0047] As the constituent material of the first electrode layer 12, for example, a sintered structure in which the above-mentioned ion-conducting metal oxide is bonded with platinum or the like, i.e., a cermet, can be used. In addition, if the oxide constituting the oxide portion 13 is an oxide represented by formula (1) above, it is preferable that the first electrode layer 12 contains the following three types (a) to (c), because when the laminate 10 of the present invention is used as a gas sensor, it is possible to operate at a lower temperature than conventional methods and variations in electromotive force between sensors are less likely to occur. (a) One or more metals selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ru, Os, and Ir. (b) Cationic conductive carbonate. (c) Oxides containing Li and at least one of Ce and Sm (hereinafter also referred to as "lithium-containing oxides"). The following explains each of these points.

[0048] The metal (a) is used primarily to impart electronic conductivity to the first electrode layer 12. The metal (a) may also be added to impart catalytic activity to the first electrode layer 12 to advance the electrochemical reaction. From this viewpoint, the metal (a) is preferably one or more selected from the group consisting of Au, Ag, Pt, Pd, Rh, Ru, Os, and Ir, and more preferably one or more selected from the group consisting of Au, Ag, and Pt. In addition, metal oxides such as zinc oxide and indium oxide that exhibit electronic conductivity can also be used.

[0049] The amount of metal or metal oxide used in (a) is preferably 20% by mass or more and 70% by mass or less, relative to the total mass of (a), (b), and (c), in order to ensure the electronic conductivity of the first electrode layer 12 and to obtain high detection performance for the target gas. From the viewpoint of making this advantage even more pronounced, the amount of metal used in (a) is more preferably 30% by mass or more and 60% by mass or less, and even more preferably 40% by mass or more and 55% by mass or less, relative to the total mass of (a), (b), and (c).

[0050] The cation-conducting carbonate in (b) is used to impart cation conductivity to the first electrode layer 12. Examples of cations include alkali metal ions such as lithium ions and sodium ions. From this viewpoint, the cation-conducting carbonate is preferably an alkali metal salt of carbonic acid. For example, the cation-conducting carbonate is preferably lithium carbonate (Li2CO3).

[0051] The amount of cation-conducting carbonate used in (b) is preferably 5% by mass or more and 55% by mass or less relative to the total mass of (a), (b), and (c), in order to efficiently form a three-phase interface within the first electrode layer 12 and to accurately detect carbon dioxide in the target atmosphere. From the viewpoint of making this advantage even more pronounced, the amount of cation-conducting carbonate used in (b) is more preferably 7% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less, relative to the total mass of (a), (b), and (c).

[0052] The lithium-containing oxide in (c) is an oxide containing Li and at least one of Ce and Sm, and plays a role in assisting the conduction of anions conducting in the oxide moiety 13 and cations conducting in the cation-conducting carbonate. The lithium-containing oxide in (c) may be a biionic conductor. For example, if the oxide moiety 13 has oxide ion conductivity and the cation-conducting carbonate has lithium ion conductivity, the lithium-containing oxide in (c) may have both oxide ion conductivity and lithium ion conductivity.

[0053] (c) For example, Li2LnO3 (where Ln represents at least one rare earth element), Li2ZrO3, Li6Zr3O7, etc. are used as materials. For example, Li2LnO3 is Li2CeO3, Li2Ce x Sm y Examples include O3 (where x and y are positive numbers and x + y = 1). Alternatively, a mixture of lithium oxide and an oxide containing at least one of Zr, Ce, and Sm may be used. These materials are preferably used in granular form.

[0054] The amount of lithium-containing oxide used in (c) is preferably 10% by mass or more and 60% by mass or less relative to the total mass of (a), (b), and (c), in order to efficiently form a three-phase interface within the first electrode layer 12 and to accurately detect the gas in the target atmosphere. From the viewpoint of making this advantage even more pronounced, the amount of lithium-containing oxide used in (c) is more preferably 20% by mass or more and 50% by mass or less, and more preferably 30% by mass or more and 40% by mass or less, relative to the total mass of (a), (b), and (c).

[0055] In the first electrode layer 12, which is composed of (a), (b), and (c) as described above, it is preferable that (a), (b), and (c) are uniformly mixed. In this state, the contact area between (a), (b), and (c) is increased, and the interfacial resistance is reduced. As a result, when the laminate 10 of the present invention is used as a gas sensor, it becomes easier to operate at even lower temperatures. Moreover, since (a), (b), and (c) are mixed together, the electromotive force becomes less dependent on the thickness of the first electrode layer 12, which has the advantage of reducing variations in electromotive force between sensors.

[0056] In the laminate 10 of the embodiment shown in Figure 1, a second electrode layer (not shown) may be placed on the surface of the oxide portion 13 opposite to the surface facing the first electrode layer 12. By placing the second electrode layer, additional functions can be added to the laminate 10. As long as the second electrode layer functions as an electrode for the oxide portion 13, there are no particular restrictions on the type of material that constitutes it, and it can be selected according to the application of the electrochemical element. For example, the second electrode layer is preferably composed of platinum group elements. Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium. These elements can be used individually or in combination of two or more. In addition, a cermet containing platinum group elements can be used as the second electrode layer. Furthermore, the same type of material as the first electrode layer can be used as the second electrode layer.

[0057] If the laminate 10 has a second electrode layer, the second electrode layer can be formed after the oxide portion 13 formation step. In this case, a firing step may be performed after the completion of the oxide portion 13 formation step, and then another firing step may be performed after the completion of the second electrode layer formation step. However, from the viewpoint of simplifying the process, it is preferable not to perform a firing step after the completion of the oxide portion 13 formation step, but to perform a firing step after the completion of the oxide portion 13 formation step and after the completion of the second electrode layer formation step. Similarly, the firing after the formation of the first electrode layer is preferably performed after the completion of the oxide portion 13 formation process and after the completion of the second electrode layer formation process.

[0058] The second electrode layer can be formed by the sputtering method as described above, or it can be manufactured using a paste. Specifically, the second electrode layer (not shown) can be suitably formed by mixing (a), (b), and (c) in a predetermined mixing ratio, adding an organic solvent to make a paste, applying the paste to the surface of the oxide portion 13 to form a coating film, and then firing the coating film. The firing temperature is preferably set to 300°C or more and 1400°C or less, more preferably 500°C or more and 1200°C or less, and even more preferably 600°C or more and 1100°C or less. The firing time is preferably set to 1 minute or more and 20 hours or less, more preferably 10 minutes or more and 15 hours or less, even more preferably 30 minutes or more and 10 hours or less, and most preferably 1 hour or more and 5 hours or less.

[0059] When preparing the paste described above, the proportion of (a) to the total amount of (a), (b), and (c) is preferably 20% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 60% by mass or less, and even more preferably 40% by mass or more and 55% by mass or less. The proportion of (b) is preferably 5% by mass or more and 55% by mass or less, more preferably 7% by mass or more and 40% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. The proportion of (c) is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 50% by mass or less, and even more preferably 20% by mass or more and 40% by mass or less.

[0060] Furthermore, when forming a second electrode layer, a firing process may be performed after the completion of the second electrode layer formation process, and then holes 14 may be formed in the substrate 11. In this case, it is not necessary to perform the hole formation process after the completion of the first electrode layer formation process and before the oxide portion 13 formation process.

[0061] The laminate of the present invention is suitably used as various gas sensors utilizing electrochemical reactions. For example, the laminate 10 shown in Figure 1 can be used as a carbon dioxide sensor or an oxygen sensor. Alternatively, the laminate of the present invention can be suitably used as a solid electrolyte membrane in a solid oxide fuel cell.

[0062] When the laminate of the present invention is used, for example, as a carbon dioxide sensor, the laminate 10 shown in Figure 1 is placed in a gas phase containing carbon dioxide (for example, air or exhaust gas from an internal combustion engine). Depending on the concentration of carbon dioxide, a reaction (see equation (A) below) occurs at the three-phase interface where the gas phase and the first electrode layer 12 are in contact, reaching an equilibrium state. Meanwhile, on the second electrode layer side (not shown), the reaction shown in equation (B) below proceeds in response to the reaction in equation (A). In other words, an electromotive force is generated between the first electrode layer 12 and the second electrode layer by the above mechanism. Since this electromotive force changes according to the concentration of carbon dioxide in the gas phase, carbon dioxide can be detected or its concentration measured using this electromotive force.

[0063] [ka]

[0064] Although the present invention has been described above based on its preferred embodiments, the present invention is not limited to the above embodiments. For example, in the embodiment shown in Figure 1, one or more intermediate layers can be formed between the oxide portion 13 and the first electrode layer 12 for the purpose of providing additional functions to the laminate 10. Similarly, one or more intermediate layers can be formed between the oxide portion 13 and the second electrode layer (not shown). [Examples]

[0065] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0066] [Example 1] (1) Formation of the first electrode layer Crystal orientation of silicon <100> A substrate with a thickness of 300 μm was prepared. The coefficient of thermal expansion of this substrate was CT. S The results are shown in Table 2 below. A 300 nm thick first electrode layer was formed on one surface of this substrate by sputtering. A 2-inch platinum target and a 4-inch SDC target were used as sputtering targets. Film deposition was performed using a co-sputtering method in which power was supplied to both targets simultaneously. DC sputtering was used for the platinum target, and RF sputtering was used for the SDC target. The argon gas flow rate was set to 50 sccm and the argon gas pressure to 4 Pa. The power was set to 200 W for each target, and sputtering was performed at room temperature. The resulting first electrode layer was porous and had a co-continuous structure in which SDC was bonded by platinum. The first electrode layer contained 12 volume% SDC and 88 volume% platinum.

[0067] (2) Manufacturing of sputtering targets for forming oxide sites The two materials were blended in a mass ratio of La2O3:SiO2 = 80:20, and ethanol was added and mixed in a ball mill. This mixture was dried, ground in a mortar, and calcined in a platinum crucible at 1650°C for 3 hours in an air atmosphere. Then, ethanol was added to this calcined product and ground in a planetary ball mill to obtain the first pre-calcined powder. Separately from this operation, the three materials were blended in a mass ratio of La2O3:SiO2:Y2O3 = 65:20:15, ethanol was added, and the mixture was mixed in a ball mill. This mixture was dried, ground in a mortar, and calcined in a platinum crucible at 1650°C for 3 hours in an air atmosphere. Then, ethanol was added to this calcined product and it was ground in a planetary ball mill to obtain a second pre-calcined powder. Ethanol was added to a mixture of the first and second pre-calcined powders and mixed in a ball mill. The mixing ratio of the two was set so that the ratio of La to Y in the target oxide portion was as shown in Table 2 below. The resulting mixed powder was dispersed in ethanol to prepare a slurry. This slurry was poured into a mold, the ethanol was removed, and then it was dried at 120°C for 4 hours to obtain a molded body. This molded body was heated at 800°C for 3 hours to deash it, and then calcined at 1620°C for 5 hours to obtain a calcined body. This calcined body was cut into a disc shape with a diameter of 100 mm and a thickness of 6 mm, and the surface was polished to obtain a sputtering target material. The composition of this target material was as shown in Table 2 below. This target material was bonded to a backing plate to obtain a sputtering target.

[0068] (3) Formation of oxide sites Using the sputtering target obtained in (2) above, an oxide moiety with a thickness of 300 nm was formed on the surface of the first electrode layer obtained in (1) above by RF sputtering. The argon gas flow rate was set to 50 sccm and the argon pressure to 0.5 Pa. The power was set to 200 W and sputtering was performed at room temperature.

[0069] (4) Formation of the second electrode layer A second electrode layer with a diameter of φ1 mm was formed on the surface of the oxide portion formed in (3) above using a metal mask under the same conditions as the first electrode layer. The laminate thus formed was fired at 900°C for 1 hour in an air atmosphere.

[0070] [Example 2] In this embodiment, no electrode layer was formed, and an oxide portion was formed directly on a silicon substrate. Otherwise, the laminate was obtained in the same manner as in Example 1.

[0071] [Examples 3 and 4] In Example 3, Al2O3 with a (0001) plane orientation was used as the substrate. In Example 4, SrTiO3 with a (100) plane orientation was used as the substrate. The coefficient of thermal expansion (CT) of these substrates is... SThe details are shown in Table 2 below. The firing temperature was 950°C, and the laminate was obtained in the same manner as in Example 2, except for these factors.

[0072] [Example 5] In preparing the oxide portion, the composition ratio of the raw materials for the second pre-calcined powder was set to La2O3:SiO2:Y2O3 = 54:21:25, and the oxide portion used had the composition shown in Table 2. The calcination temperature was 950°C, and the laminate was obtained in the same manner as in Example 2.

[0073] [Comparative Example 1] In preparing the oxide portion, the composition ratio of the raw materials for the second pre-calcined body powder was set to La2O3:SiO2 = 80:20, and the oxide portion used had the composition shown in Table 2. This oxide portion did not contain yttrium. Otherwise, the laminate was obtained in the same manner as in Example 1.

[0074] [Comparative Example 2] The oxide moieties used had the compositions shown in Table 2. These oxide moieties did not contain yttrium. Otherwise, the laminate was obtained in the same manner as in Example 2.

[0075] 〔evaluation〕 The crystal structure of the oxide moiety, the position and space group of the 004 diffraction peak, and the coefficient of linear expansion of the oxide moiety in the laminates obtained in the examples and comparative examples were measured using the method described below. The results are shown in Table 2. Furthermore, the presence or absence of crack formation after heating and the crack formation load were measured for the laminates obtained in the examples and comparative examples using the method described below. In addition, the conductivity of the laminates obtained in Example 1 and Comparative Example 1 was measured using the method described below. The results are shown in Table 2.

[0076] [Crystal structure of oxide portion, position and space group of 004 ​​diffraction peak] A Rigaku RINT-TTRIII XRD measurement system was used. CuKα radiation (λ=1.5418 Å) was used as the radiation source, and measurements were performed in the range of 2θ=10° to 80°. The apatite-type crystal structure was confirmed by the 004 diffraction peak located at 2θ=51.9°±0.9° in the XRD pattern.

[0077] [Coefficient of linear expansion of oxide sites] The coefficient of linear thermal expansion of the oxide portion was measured by performing XRD analysis while varying the temperature. Specifically, first, powders of calcined bodies with different compositions were prepared using the same method as in (2) of Example 1. The La2O3:SiO2:Y2O3 ratios were 80:20:0 (Comparative Examples 1 and 2), 65:20:15 (Examples 1 to 4), and 54:21:25 (Example 5), respectively. To these, α-Al2O3 powder was added as an internal standard, such that the mass ratio of calcined body powder:α-Al2O3 was 75:25, and the mixture was mixed in a mortar for 5 minutes. A Rigaku Smart Lab XRD measurement system was used. An Anton Paar DHS1100 was used as the heating stage. Graphite was used as the heat shield for the heating stage. The measurement conditions were as follows: source CuKα (λ=1.5418Å), tube voltage 40kV, tube current 30mA, scanning method 2θ / θ, measurement range 2θ=15°~80°, sampling width=0.02°, scanning speed 1.5° / min, and measurement temperatures of 30℃, 100℃, 300℃, 500℃, 700℃, and 900℃. The lattice constants of the calcined powder were determined from the obtained XRD spectra using the analysis software Rigaku PDXL2. After correcting for diffraction angle errors due to equipment errors associated with heating using the diffraction peak of α-Al2O3 added as an internal standard, the diffraction peaks of the calcined powder were peak-fitted using the WPPF method, and the lattice constants for the a-axis and c-axis at each temperature were determined by refining the lattice constants in the range of 30° to 80°. The determined lattice constants were plotted against temperature, approximated by a straight line using the least squares method, and the slope (Å / K) was determined. The value obtained by dividing the slope (Å / K) by the lattice constant at a temperature of 30°C was the coefficient of linear expansion (10°C) of the calcined powder. -6The formula was set to / K). The results are shown in Table 2.

[0078] [Riettveld method] To investigate the atomic sites to which the Y atoms coordinate in the apatite-type crystal structure of the oxide portion, XRD spectra were acquired and analyzed using the Rietveld method. Specifically, profile fitting was performed using the program RIETAN-FP (version 2.8.3) to refine the atomic positions and anisotropy temperature factors of La2, Y1, Si1, and O4. As measurement samples, powders of calcined bodies with mass ratios of La2O3:SiO2:Y2O3 of 80:20:0 and 65:20:15 were prepared by the same method as in (2) of Example 1. A Rigaku Smart Lab XRD analyzer was used to acquire the XRD spectra. The measurement conditions were: source CuKα (λ=1.5418Å), tube voltage 45kV, tube current 200mA, scanning method 2θ / θ, measurement range 2θ=5°~140°, sampling width=0.01°, and scanning speed 0.4° / min. In the Rietveld method, a segmented pseudo-Voigt function was used as the profile function and fitted to the measured values ​​of the XRD pattern by the least squares method, along with zero-point correction, background, (001) orientation parameter, and lattice constant. There are two crystallographically distinct sites (Wyckoff symbols 4f and 6h) occupied by La atoms. Detailed examination suggested a decrease in electron density compared to the case where only the 4f site is 100% occupied by La atoms. This means that the La atom occupancy rate at this site is less than 100%, i.e., there is a deficiency of La atoms, or Y atoms with fewer electrons than La atoms are substituting for some of the La atoms, or both. Since the abundance ratio of La atoms to Y atoms is constant from the above chemical composition, the ratio of Y atoms can be automatically determined based on the ratio of each La atom present in the 4f and 6h sites. Specifically, the Y atom occupancy rate at the 4f site is [0.17647 * La atom occupancy rate at the 4f site + 0.26471 * La atom occupancy rate at the 6h site]. In the analysis, these two La atom occupancy rates were refined independently. While it is theoretically possible for atom occupancy rates to be negative or exceed 100%, this is clearly unreasonable considering the actual crystal structure. However, the results of the analysis for Examples 1 to 4, as shown in Table 1 below, show that the sum of the La and Y atom occupancy rates at the 4f site is 88%, and the La atom occupancy rate at the 6h site is 97%, both positive and below 100%, which is reasonable. Therefore, the reliability of this analysis is high.

[0079] [Table 1]

[0080] [Presence or absence of crack formation after heating] For the laminated structure, the thin film was observed using a JEOL JSM-7900F scanning microscope (SEM) at an incident voltage of 5kV and room temperature at 5000x and 10000x magnification to confirm the presence or absence of cracks.

[0081] [Crack-inducing load] The crack initiation load was measured for the laminates obtained in Examples 1 to 4 and Comparative Examples 1 and 2 by nanoindentation testing. A HYSITRON TI preminer Multi Scale was used as the measuring instrument. A Berkovich indenter was used with a maximum load of 1000 mN, and measurements were taken with loading for 5 seconds, maximum load holding time of 2 seconds, and unloading for 5 seconds. When a crack occurs in the object being measured, a slight bend appears in the load-displacement curve. This bend was defined as the crack initiation load.

[0082] 〔conductivity〕 The laminates obtained in Example 1 and Comparative Example 1 were evaluated using electrochemical measurements. Specifically, measurements were performed using the AC impedance method with a Solartron SI1260. The measurements were performed at a measurement amplitude of 30 mV, with frequencies from 1 MHz to 1 kHz, and at 600°C. After creating a Nyquist plot using the measurement results, the value at the intersection with the real axis when performing arc fitting in the aforementioned frequency range was evaluated as the resistance value. Based on this resistance value, the conductivity was output, given that the electrode area of ​​the laminate was φ1 mm and the electrolyte thickness was 300 nm.

[0083] [Table 2]

[0084] As is clear from the results shown in Table 2, no cracks caused by heating were observed in the laminates obtained in each example. In contrast, the laminate obtained in the comparative example developed cracks upon heating. [Industrial applicability]

[0085] The laminate of the present invention exhibits ionic conductivity while suppressing the occurrence of damage such as cracks.

Claims

1. A laminate comprising a substrate, an oxide portion located on the substrate, a first electrode layer located between the substrate and the oxide portion, and a second electrode layer located on the surface of the oxide portion opposite to the surface facing the first electrode layer, The substrate has through holes extending in the thickness direction of the substrate in the region facing the substrate and the first electrode layer. The first electrode layer and the second electrode layer are porous. The oxide constituting the oxide portion contains at least two rare earth elements, silicon, and oxygen, and in the X-ray diffraction pattern, a diffraction peak originating from the (004) plane is observed at the position 2θ = 51.9° ± 0.9°, and has an apatite-type crystal structure. A laminate in which the ratio of the linear expansion coefficient of the oxide in the a-axis direction to the linear expansion coefficient of the substrate is 0.15 or more and 1.45 or less.

2. The laminate according to claim 1, wherein the substrate contains silicon.

3. The laminate according to claim 2, wherein the substrate comprises at least one of silicon oxide and crystalline silicon.

4. The laminate according to any one of claims 1 to 3, wherein the oxide comprises a lanthanum group element and at least one of yttrium and scandium.

5. The aforementioned oxide is, Formula (1): A ９．３＋ｘ-ａ Y ａ [Si ６．０－ｙ M ｙ ]O ２６．０＋ｚ A laminate according to any one of claims 1 to 4, represented by the formula (wherein A is one or more elements selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Be, Mg, Ca, Sr, and Ba, and containing at least La. M is one or more elements selected from the group consisting of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Ga, Ge, Zr, Ta, Nb, B, Zn, Sn, W, and Mo. x is a number between -1.4 and 1.

5. y is a number between 0.0 and 3.

0. z is a number between -5.0 and 5.

2. a is a number between 0.1 and 10.

4. The ratio of moles of A to moles of Si is between 1.4 and 3.7.)

6. The oxide represented by formula (1) is in space group P6 ３ / m has In equation (1), A includes at least La, The laminate according to claim 5, wherein, of the sites occupied by La, there are more Y at the 4f site than at the Wyckoff position 6h site.

7. A laminate according to any one of claims 1 to 6, used as a gas sensor or a solid oxide fuel cell.

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