Oxide ion conductive solid electrolyte

Abstract

An oxide ion-conducting solid electrolyte that comprises a mayenite-type compound having a typical composition represented by Ca12Al14O33 and 9-30 mol%, in terms of TiO2, of titanium (Ti).

Description

[Technical Field]

[0001] This invention relates to an oxide ion conductive solid electrolyte. [Background technology]

[0002] Solid electrolytes with oxide ion transport properties have various applications, including solid oxide fuel cells (SOFCs), solid oxide electrolytic cells (SOECs), oxygen sensors, and oxygen pumps. In recent years, highly efficient energy systems combining SOFCs and SOECs have attracted attention as one way to realize the Power to Gas / Chemical technology concept, which is gaining traction for the widespread adoption of renewable energy.

[0003] Both SOFCs and SOECs are electrochemical cells that operate at high temperatures. The former can handle various fuels such as hydrogen, carbon monoxide, and methane, while the latter can electrolyze the water and carbon dioxide produced by the operation of SOFCs and convert them back into hydrogen and carbon monoxide.

[0004] SOFCs and SOECs have a solid electrolyte placed between two electrodes, and they operate through the conduction of oxide ions within this solid electrolyte. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] FMLea, CHDesch, The Chemistry of Cement and Concrete, 2nd ed., p.52, Edward Arnold&Co., London, 1956 [Non-Patent Document 2] M. Lacerda et al., “High Oxide ion conductivity in Ca12Al14O33” Nature, vol. 332, P525, 7, April (1988) [Non-Patent Document 3] J.Salasin et al.Crystals vol.7, 143(2017) [Non-Patent Document 4] NEBrese et al.Acta Crystallogr. vol.B47,192-197(1991) [Non-Patent Document 5] A.Pedone et al.J.Phys.Chem.B 110, 11780-11795(2006) [Overview of the project] [Problems that the invention aims to solve]

[0006] Many materials have been studied as solid electrolytes for SOFCs and SOECs, including yttria-stabilized zirconia (YSZ) and scandia-stabilized zirconia (ScSZ).

[0007] However, even in YSZ and ScSZ, the oxide ion conductivity is still not sufficient, and there is a need for solid electrolytes with higher oxide ion conductivity.

[0008] This invention has been made in view of the above background, and aims to provide a solid electrolyte having high oxide ion conductivity that can replace conventional materials. [Means for solving the problem]

[0009] In this invention, A solid electrolyte that conducts oxide ions, Ca 12 Al 14 O 33 A meienite-type compound having a representative composition represented by [the given formula] and an oxide ion-conducting solid electrolyte containing 9 mol% to 30 mol% titanium (Ti) in terms of TiO2 are provided.

[0010] Furthermore, in this invention, A solid electrolyte that conducts oxide ions, Ca 12Al 14 O 33 It has a melilite-type compound having a representative composition represented by, The melilite-type compound provides an oxide ion conductive solid electrolyte containing titanium (Ti) in an amount of 9 mol% to 30 mol% in terms of TiO2.

Advantages of the Invention

[0011] In the present invention, a solid electrolyte having high oxide ion conductivity that can replace conventional materials can be provided.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view schematically showing one configuration example of a SOFC. [Figure 2] It is a diagram schematically showing an example of the flow of a method for producing an oxide ion conductive solid electrolyte according to an embodiment of the present invention. [Figure 3] It is a diagram schematically showing an example of the flow of another method for producing an oxide ion conductive solid electrolyte according to an embodiment of the present invention. [Figure 4] It is a diagram showing the result of evaluating the influence of the addition of Ti on the ion conductivity in a melilite-type compound having a C12A7 structure by simulation. [Figure 5] It is a diagram showing the X-ray diffraction pattern of an oxide ion conductive solid electrolyte (Sample 1) according to an embodiment of the present invention. [Figure 6] It is a diagram showing the Cole-Cole plot obtained in Sample 1. [Figure 7] It is a diagram showing the Cole-Cole plot obtained in Sample 2. [Figure 8] It is a diagram showing the Cole-Cole plot obtained in Sample 11. [Figure 9] It is a diagram showing the Cole-Cole plot obtained in Sample 12.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, an embodiment of the present invention will be described.

[0014] (Oxide ion conductive solid electrolyte according to an embodiment of the present invention) In one embodiment of the present invention, an oxide ion conductive solid electrolyte comprising a mayenite-type compound having a representative composition represented by Ca 12 Al 14 O 33 is provided, wherein the mayenite-type compound contains titanium (Ti) in an amount of 9 mol% to 30 mol% in terms of TiO2.

[0015] The oxide ion conductive solid electrolyte according to an embodiment of the present invention (hereinafter referred to as "the first solid electrolyte") contains a mayenite-type compound having a C12A7 structure (Ca 12 Al 14 O 33 33 ).

[0016] The mayenite-type compound has a representative composition represented by 12CaO·7Al2O3 and has a characteristic crystal structure having three-dimensionally connected voids (cages) with a diameter of about 0.4 nm.

[0017] The framework constituting this cage is positively charged and forms 12 cages per unit cell. One-sixth of this cage is occupied by oxide ions inside in order to satisfy the electrical neutrality condition of the crystal. However, the oxide ions in this cage have characteristics chemically different from those of other oxygen ions constituting the framework. Therefore, the oxide ions in the cage are particularly called free oxide ions.

[0018] The mayenite-type compound is also represented by the composition formula [Ca 24 Al 28 O 64 4+ (O 2- )2 (Non-Patent Document 1). ​

[0019] As mentioned above, meienite-type compounds contain free oxide ions within their cage, and therefore may be able to function as oxide ion conductors (Non-Patent Literature 2).

[0020] However, analysis by the present inventors has shown that the ionic conductivity of meienite-type compounds having the above composition formula is not very high (for example, about 1 / 10 of YSZ).

[0021] The inventors of this invention have been diligently researching and developing methods to improve the ionic conductivity of meienite-type compounds. They have discovered that adding titanium (Ti) to meienite-type compounds significantly increases their ionic conductivity, leading to the present invention.

[0022] Therefore, in the oxide ion-conducting solid electrolyte according to one embodiment of the present invention, the meienite-type compound contains Ti.

[0023] In the present invention, the constituent elements of the meienite compound are not limited to calcium (Ca), aluminum (Al), and oxygen (O), as long as it has a C12A7 crystal structure consisting of calcium (Ca), aluminum (Al), and oxygen (O). For example, it is known that a portion of the calcium (Ca) can be substituted with one or more atoms selected from the group consisting of magnesium (Mg), strontium (Sr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), dysprosium (Dy), holmium (Ho), ytterbium (Yb), and tantalum (Ta). Furthermore, it is known that some aluminum (Al) can be substituted with one or more atoms selected from the group consisting of phosphorus (P), silicon (Si), gallium (Ga), vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), and niobium (Nb) (Non-Patent Literature 3).

[0024] In particular, in one embodiment of the present invention, Ti is added in an amount of 9 mol% or more in terms of TiO2. This is because if the Ti content is less than 9 mol%, no significant effect is observed on the ionic conductivity of the meienite-type compound. However, if Ti is added in excess, it becomes difficult to incorporate Ti into the meienite-type crystal structure. Therefore, in the oxide ion-conducting solid electrolyte according to one embodiment of the present invention, the Ti content is limited to 30 mol% or less.

[0025] The Ti content is preferably 10 mol% or more, and more preferably 15 mol% or more.

[0026] In the oxide ion-conducting solid electrolyte according to one embodiment of the present invention, the added Ti is considered to be substituted at the sites of aluminum (Al) atoms in the meienite-type compound. The molar ratio of Ti atoms to Al atoms, Ti / Al, may be 0.15 ≤ Ti / Al ≤ 0.50.

[0027] An oxide ion-conducting solid electrolyte according to one embodiment of the present invention has significantly higher ionic conductivity and can therefore be used as a solid electrolyte to replace conventional materials.

[0028] Currently, the following reasons are considered to be the cause of increased ionic conductivity in the meienite-type compound by incorporating a predetermined amount of Ti in one embodiment of the present invention.

[0029] When Ti is added to a meienite-type compound, the Ti atom is thought to preferentially substituted into the site of the Al atom. However, while the Al atom is trivalent, the Ti atom is tetravalent. Therefore, when the Al atom is substituted for the Ti atom, the concentration of oxide ions increases due to electrical neutrality.

[0030] In the case of typical compounds, if excess oxide ions are inserted between the stigma, the compound may become unstable or impossible to synthesize. Alternatively, problems such as a decrease in ionic conductivity may occur.

[0031] In contrast, it is thought that in meienite-type compounds, the ionic conductivity is improved simply by increasing the concentration of free oxide ions within the cage, which act as carriers for ion conduction, while maintaining the crystalline structure of the compound.

[0032] Based on these considerations, it is possible that the ionic conductivity of the meienite-type compound may improve even when tetravalent ions other than Ti are added. However, according to the inventors' experiments, no significant improvement in ionic conductivity was observed when silicon (Si) or germanium (Ge), which are tetravalent ions like Ti, were added to the meienite-type compound.

[0033] These results suggest that the ionic radius of the added element and its chemical bonding state with the surrounding oxygen may be influencing the ionic conductivity of the meienite-type compound. The strength of the electrostatic bond between atoms constituting the crystal is called bond valence, and when comparing Si, Ge, and Ti, the bond valence parameter that determines the magnitude of the bond valence is largest for Ti (Non-Patent Literature 4). In other words, it is expected that the bond between the oxygen constituting the crystal framework and the added Ti will become stronger, weakening the bond between free oxide ions and the crystal framework, making it easier for free oxide ions to move, and as a result, the ionic conductivity will improve.

[0034] However, the mechanism for improving ionic conductivity described above is based on current experimental considerations, and the oxide ion-conducting solid electrolyte according to one embodiment of the present invention may have improved ionic conductivity through a different mechanism.

[0035] (Other features) The oxide ion-conducting solid electrolyte according to one embodiment of the present invention is a ceramic and therefore has high high-temperature stability. For example, the oxide ion-conducting solid electrolyte according to one embodiment of the present invention can be used stably even in a temperature range of 800°C or higher.

[0036] (Application) An oxide ion-conducting solid electrolyte according to one embodiment of the present invention is stable even at high temperatures and has significantly high oxide ion conductivity. Therefore, the oxide ion-conducting solid electrolyte according to one embodiment of the present invention can be applied, for example, as a solid electrolyte for SOFCs, SOECs, oxygen sensors, and oxygen pumps.

[0037] Figure 1 shows a schematic representation of the SOFC configuration.

[0038] As shown in Figure 1, the SOFC 100 has an oxygen electrode 110, a fuel electrode 120, and a solid electrolyte layer 130 between the two electrodes.

[0039] When SOFC100 with this configuration is in operation, the following reactions occur at the oxygen electrode 110, for example: O2+4e - →2O 2- (1) Formula Oxide ions generated at the oxygen electrode 110 pass through the solid electrolyte layer 130 and reach the fuel electrode 120 on the opposite side. At the fuel electrode 120, for example, the following reactions occur: 2H2 + 2O 2- →2H2O+4e - Equation (2) Therefore, when SOFC100 is connected to an external load, the reactions in equations (1) and (2) continue, and power can be supplied to the external load.

[0040] On the other hand, SOEC typically has a configuration similar to that of SOFC100 shown in Figure 1.

[0041] However, in SOEC, as shown in Figure 1 above, the following reaction occurs at the oxygen electrode 110: 20 2- →O2+4e - Equation (3) Furthermore, at the fuel electrode 120, for example, the following reaction occurs: 2H2O + 4e - →2H2+2O 2- (4) Formula Oxide ions generated at the fuel electrode 120 pass through the solid electrolyte 130 and reach the oxygen electrode 110 on the opposite side. Therefore, when the SOEC is connected to an external power source, reactions (3) and (4) continue.

[0042] An oxide ion-conducting solid electrolyte according to one embodiment of the present invention can be used as an "electrolyte layer" placed between two electrodes in such an electrochemical cell, as well as as an "electrolyte component" contained in the electrodes.

[0043] Furthermore, the solid electrolyte according to one embodiment of the present invention may be used in any form. For example, the solid electrolyte according to one embodiment of the present invention may be provided as a powder. Alternatively, the solid electrolyte according to one embodiment of the present invention may be mixed with a solvent and / or binder and provided in the form of a slurry, paste, or dispersion.

[0044] In addition to these, various other usage scenarios can be envisioned.

[0045] (Method for producing an oxide ion-conducting solid electrolyte according to one embodiment of the present invention) Next, with reference to Figure 2, an example of a method for producing an oxide ion-conducting solid electrolyte according to one embodiment of the present invention will be described.

[0046] Figure 2 schematically shows an example of a flow diagram of a method for producing an oxide ion conductive solid electrolyte according to one embodiment of the present invention (hereinafter referred to as the "first manufacturing method").

[0047] As shown in Figure 2, the first manufacturing method is (1) A step of mixing Ca source, Al source, and Ti source in predetermined proportions to obtain a mixed powder (step S110), (2) A step of calcining the mixed powder to obtain calcined powder (step S120), (3) A step of sintering the calcined powder to obtain a sintered body (step S130), It holds.

[0048] The following explains each step.

[0049] (Step S110) First, a mixed powder is prepared. For this purpose, Ca source, Al source, and Ti source are mixed in predetermined proportions.

[0050] The Ca source may be selected from, for example, metallic calcium, calcium carbonate, calcium oxide, calcium hydroxide, calcium nitrate, and calcium acetate.

[0051] The Al source may be selected from, for example, metallic aluminum, α-alumina, γ-alumina, aluminum hydroxide, aluminum nitrate, and aluminum lactate.

[0052] The Ti source may be selected from, for example, metallic titanium, rutile-type titanium oxide, anatase-type titanium oxide, titanium(II) oxide, and titanium(III) oxide.

[0053] Each raw material is weighed and mixed to obtain meienite with the desired composition.

[0054] The mixing method is not particularly limited, as long as a uniform mixed powder is obtained.

[0055] (Process S120) Next, the mixed powder is calcined.

[0056] The calcination process is performed to remove compounds such as carbonic acid and nitric acid contained in the mixed powder, thereby facilitating the formation of the desired meienite-type compound in the subsequent sintering process.

[0057] While there are no particular limitations on the calcination conditions, a calcination temperature of 1000°C or higher is preferable to obtain the desired mixed oxide. However, if the calcination temperature is too high, excessive crystallization will occur in the mixed powder. Therefore, a calcination temperature of 1300°C or lower is preferable.

[0058] The calcination time is, for example, around 5 to 24 hours. However, the calcination time also varies depending on the calcination temperature; the higher the calcination temperature, the shorter the calcination time can be.

[0059] This yields calcined powder.

[0060] The calcined powder may be ground as needed. The average particle size after grinding may be, for example, in the range of 1 μm to 100 μm.

[0061] (Step S130) Next, the calcined powder is sintered.

[0062] The sintering process is carried out to obtain a dense sintered body having the desired crystalline phase.

[0063] Alternatively, the calcined powder may be molded before the sintering process, and the resulting molded body may be used to carry out the sintering process.

[0064] The molding conditions are not particularly limited, and general molding methods such as uniaxial molding or hydrostatic molding may be employed.

[0065] The sintering method is not particularly limited; for example, the calcined powder or molded body may be sintered by a non-pressure sintering method under normal pressure.

[0066] Alternatively, the calcined powder may be sintered using a pressure sintering method such as hot press sintering or discharge plasma sintering. In this case, molding and sintering may be performed in a single process.

[0067] The sintering temperature is not particularly limited as long as a suitable sintered body is obtained, but a range of 1200°C to 1400°C is preferred. If the sintering temperature is too low, a dense sintered body may not be obtained. Conversely, if the sintering temperature is too high, melting of the material being processed may occur.

[0068] It is desirable to select the optimal sintering time according to the sintering temperature. Generally, the higher the sintering temperature, the shorter the time required for sintering to complete.

[0069] The optimal sintering time varies depending on the sintering temperature, but for non-pressure sintering, it is approximately 5 to 48 hours, while for pressure sintering using discharge plasma, it is approximately 5 to 60 minutes.

[0070] Furthermore, when using a carbon container for pressure sintering, carbon may adhere to the surface of the sintered body. In such cases, the attached carbon can be removed by heat treatment at 800°C to 1000°C for about 5 hours under atmospheric pressure.

[0071] By following the above steps, an oxide ion-conducting solid electrolyte according to one embodiment of the present invention can be manufactured.

[0072] (Another method for producing an oxide ion conductive solid electrolyte according to one embodiment of the present invention) Next, with reference to Figure 3, an example of another method for producing an oxide ion-conducting solid electrolyte according to one embodiment of the present invention will be described.

[0073] Figure 3 schematically shows an example of a flow chart of another method for producing an oxide ion conductive solid electrolyte according to one embodiment of the present invention (hereinafter referred to as the "second manufacturing method").

[0074] As shown in Figure 3, the second manufacturing method is (1) A step of mixing a Ca source and an Al source in a predetermined ratio to obtain a first mixed powder (step S210), (2) A step of calcining the first mixed powder to obtain the first calcined powder (step S220), (3) A step of mixing the first calcined powder and the Ti source in a predetermined ratio to obtain a second mixed powder (step S230), (4) A step of calcining the second mixed powder to obtain the second calcined powder (step S240), (5) A step of sintering the second calcined powder to obtain a sintered body (step S250), It holds.

[0075] Each step in the second manufacturing method can be easily understood by those skilled in the art from the description of steps S110 to S130 in the first manufacturing method described above. Therefore, a detailed explanation of each step is omitted here.

[0076] However, in the second manufacturing method, unlike the first manufacturing method, the oxide ion conductive solid electrolyte is produced through two calcination steps (steps S220 and S240).

[0077] In this case, compared to the first manufacturing method, where a mixed powder containing a Ca source, an Al source, and a Ti source is calcined all at once, an oxide ion-conducting solid electrolyte with a more homogeneous composition can be produced.

[0078] In other words, in the first manufacturing method, highly reactive Ca and Ti may react, potentially forming a different phase. In contrast, in the second manufacturing method, a calcined powder in which Ca and Al have reacted and bonded can be prepared in advance during the first calcination step (step S220). Therefore, in the second calcination step (step S240), Ca, Al, and Ti can be bonded to each other more reliably at the desired sites within the meienite-type compound.

[0079] The method for producing an oxide ion-conducting solid electrolyte according to one embodiment of the present invention has been described above, with the first and second production methods as examples. However, the above description is merely an example, and the oxide ion-conducting solid electrolyte according to one embodiment of the present invention may be produced by other methods such as the hydrothermal method, the sol-gel method, and the liquid-phase combustion method. [Examples]

[0080] The following describes embodiments of the present invention.

[0081] (Simulation evaluation) The effect of Ti addition on the ionic conductivity of a C12A7 structured meienite compound was evaluated by simulation.

[0082] In the simulation, the relationship between the mean squared displacement (MSD) of oxide ions in the material and the elapsed time was calculated using classical molecular dynamics calculations at 1 atmosphere and 1200 K.

[0083] The code used for the calculations was LAMMPS. For the input parameters, the inter-body potentials of the constituent elements of each material, we used the values ​​reported by Pedone et al. (see Non-Patent Document 5).

[0084] In a supercell with an expanded unit cell of 6×6×6, molecular dynamics simulations were performed using an NPT ensemble for 1 nanosecond intervals for systems in which 0%, 7%, and 14% of Al were substituted with Ti in molar ratios. Furthermore, after the temperature, internal energy, and lattice constant stabilized, molecular dynamics simulations were performed using an NVE ensemble for 1 nanosecond intervals.

[0085] The following three compounds were used for the calculations: (i) Unsubstituted meienite-type compounds, i.e., 12CaO·7Al2O3 compounds, (ii) A compound in which 7% of the Al atoms in the meienite-type compound are replaced with Ti atoms (Ti accounts for 5 mol% of the total in terms of TiO2), and (iii) A compound in which 14% of the Al atoms in a meienite-type compound are replaced with Ti atoms (Ti represents 10 mol% of the total in terms of TiO2).

[0086] Figure 4 shows the simulation results for each of the compounds (i) to (iii).

[0087] In Figure 4, the horizontal axis represents elapsed time, and the vertical axis represents the medium-stressed daily dose (MSD) of oxygen.

[0088] The slope of the MSD is proportional to the diffusion coefficient. Therefore, Figure 4 shows that materials with a larger MSD slope allow oxide ions to move more easily within the meienite-type compound.

[0089] In Figure 4, the slope of the MSD is defined as the slope in the portion where the behavior of each compound is represented by a straight line.

[0090] Table 1 below summarizes the slopes of the MSD for each of the three compounds.

[0091] [Table 1] As shown in Figure 4 and Table 1, in compounds (ii) and (iii), in which some of the Al atoms in the meienite-type compound were replaced with Ti atoms, the slope of the MSD increased compared to the unsubstituted meienite-type compound (i).

[0092] However, in compound (ii), the increasing trend in the slope is not as pronounced compared to compound (i). The slope of the MSD in compound (ii) was about 1.2 times that of compound (i).

[0093] In contrast, the slope of MSD in compound (iii) was approximately four times greater than that of compound (i), indicating a significant increase in the slope of MSD.

[0094] This indicates that in meienite-type compounds, substituting 14% of the Al atoms with Ti atoms significantly improves the ionic conductivity of oxide ions.

[0095] (Example 1) The sintered body was fabricated using the following method.

[0096] [Mixing Process] Calcium carbonate (4.20g), α-alumina (2.12g), and rutile-type titanium dioxide (0.55g) were weighed separately. These were placed in a pot containing φ5mm zirconia balls and 10cc of isopropanol, and the mixture was ground and mixed for 3 hours using a planetary ball mill. Next, the mixed powder was dried at 100°C to remove the isopropanol. Furthermore, the mixed powder was separated from the zirconia balls by sieving.

[0097] [Calibration process] The resulting mixed powder was placed in an alumina crucible and calcined in air at 1200°C for 5 hours. The resulting sample was ground in an agate mortar to prepare calcined powder.

[0098] [Sintering process] 1 g of calcined powder was placed in a φ1.5 cm carbide die, and uniaxial forming was performed by applying a pressure of 20 kN with a hydraulic press. Furthermore, hydrostatic forming was performed at 196 MPa to produce a φ1.5 cm pellet. The pellet was heat-treated in air at 1300°C for 12 hours to obtain a sintered body with a diameter of φ1.3 cm and a thickness of 2 mm.

[0099] The resulting sintered body is referred to as "Sample 1". In Sample 1, the Ti content is 10 mol% in terms of TiO2, and the molar ratio Ti / Al is 0.17.

[0100] (Example 2) A sintered body was prepared using the same method as in Example 1. However, in Example 2, in the aforementioned [mixing step], calcium carbonate (4.37 g), α-alumina (1.90 g), and rutile-type titanium oxide (0.82 g) were mixed to prepare a mixed powder. The other steps were the same as in Example 1.

[0101] The resulting sintered body is referred to as "Sample 2". In Sample 2, the Ti content is 15 mol% in terms of TiO2, and the molar ratio Ti / Al is 0.27.

[0102] (Example 11) A sintered body was prepared using the same method as in Example 1. However, in Example 11, in the aforementioned [mixing step], calcium carbonate (4.12 g) and α-alumina (2.57 g) were mixed to prepare a mixed powder. That is, the mixed powder was prepared without adding a Ti source. The other steps were the same as in Example 1.

[0103] The resulting sintered body is referred to as "Sample 11".

[0104] (Example 12) A sintered body was prepared using the same method as in Example 1. However, in Example 12, in the aforementioned [mixing step], calcium carbonate (4.24 g), α-alumina (2.23 g), and rutile-type titanium oxide (0.42 g) were mixed to prepare a mixed powder. The other steps were the same as in Example 1.

[0105] The resulting sintered body is referred to as "Sample 12". In Sample 12, the Ti content is 8 mol% in terms of TiO2, and the molar ratio Ti / Al is 0.12.

[0106] Table 2 below summarizes the amount of Ti and the molar ratio Ti / Al contained in each sample.

[0107] [Table 2] (evaluation) The following evaluations were performed using each sample.

[0108] (X-ray diffraction analysis) X-ray diffraction analysis was performed using Sample 1 and Sample 2.

[0109] Figure 5 shows the X-ray diffraction pattern obtained for Sample 1. In Figure 5, each peak indicated by a wedge symbol corresponds to the crystalline phase of the meienite-type compound.

[0110] Thus, in Sample 1, it was confirmed that the sintered body was a meienite-type compound.

[0111] Similar results were obtained in Sample 2.

[0112] (Resistivity measurement) Resistivity measurements were performed on each sample. The impedance method was used for resistivity measurement.

[0113] First, the surface of each sample was polished with sandpaper ranging from #80 to #1000 to remove the surface layer and smooth the surface.

[0114] Next, a platinum electrode with a diameter of 6 mm and a thickness of 10 μm was placed on the polished surface via platinum paste. This sample was heat-treated at 1000°C for 15 minutes in an air atmosphere to solidify the platinum paste.

[0115] Next, the sample was placed in an electric furnace under an atmospheric environment. The sample was also connected to a potentogalvanostat (Biologic SP-150) via a platinum wire coupled to a platinum electrode.

[0116] Next, the sample was heated to 850°C and held for 120 minutes to stabilize its temperature.

[0117] After the sample temperature stabilized, impedance measurements were performed and a Cole-Cole plot was created. The measurement frequency was set from 1 MHz to 100 mHz.

[0118] The resulting Cole-Cole plot was fitted to a semicircle, and the intersection points (two points) of the arc of the fitting curve with the real number axis were determined. This allowed us to determine the resistance on the high-frequency side (resistivity 1) and the resistance on the low-frequency side (resistivity 2).

[0119] Figures 6 to 9 show the Cole-Cole plots obtained for Sample 1 to Sample 2 and Sample 11 to Sample 12, respectively.

[0120] These figures also show the arcs obtained by curve fitting of the measurement results.

[0121] Furthermore, Table 3 below summarizes the results obtained for each sample.

[0122] [Table 3] The results show that in both Sample 1 and Sample 2, the resistivity 1 and resistivity 2 are significantly reduced compared to Sample 11, which is an unsubstituted meienite-type compound.

[0123] In particular, in sample 2, the resistivity 1 decreased to approximately 1 / 9 of that in sample 11. Also, the resistivity 2 decreased to approximately 1 / 15 of that in sample 11. On the other hand, in sample 12, while resistivity 1 and resistivity 2 decreased compared to sample 11, the degree of decrease was not very significant.

[0124] Thus, in the meienite-type compounds, it was found that the resistivity was significantly reduced in samples to which 10 mol% and 15 mol% of Ti (in terms of TiO2) were added.

[0125] These results suggest that a solid electrolyte composed of a meienite-type compound with more than 8 mol% Ti added can exhibit good ionic conductivity.

[0126] This application claims priority based on Japanese Patent Application No. 2021-075287, filed on 27 April 2021, and the entire contents of the said Japanese application are incorporated herein by reference.

Claims

1. A solid electrolyte that conducts oxide ions, Ca １２ Al １４ O ３３ It has a meienite-type compound having a representative composition represented by the following: The aforementioned meienite-type compound is TiO ２ In terms of conversion, it contains 9 mol% to 30 mol% titanium (Ti). The aforementioned Ti is an oxide ion-conducting solid electrolyte located at the site of the Al atom.

2. The oxide ion conductive solid electrolyte according to claim 1, wherein the ratio of Ti atoms to Al atoms, Ti / Al, satisfies 0.15 ≤ Ti / Al ≤ 0.

50.

3. An electrochemical cell comprising an oxide ion conductive solid electrolyte according to claim 1 or 2.

4. A fuel cell comprising an oxide ion conductive solid electrolyte according to claim 1 or 2.

5. An electrolytic cell comprising an oxide ion conductive solid electrolyte according to claim 1 or 2.

6. An oxygen sensor comprising an oxide ion conductive solid electrolyte according to claim 1 or 2.

7. An oxygen pump comprising an oxide ion-conducting solid electrolyte according to claim 1 or 2.

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