Non-stoichiometric layered perovskite and method for recovering electrical conductivity thereof

Abstract

The present invention relates to a non-stoichiometric layered perovskite in which electrical conductivity is reversibly recovered when the temperature is repeatedly raised and lowered within a predetermined temperature range between an oxygen and non-oxygen atmosphere, and a method for recovering the electrical conductivity thereof. The non-stoichiometric layered perovskite has a non-stoichiometric composition satisfying Formula 1, and thus can exhibit reversible electrical conductivity characteristics satisfying Formula 1.

Description

Technology Field

[0001] The present invention relates to a non-stoichiometric layered perovskite and a method for restoring the electrical conductivity thereof. Background Technology

[0002] Solid oxide fuel cells (SOFCs) are the most efficient fuel cells for converting chemical energy into electrical energy, and large-capacity SOFC power generation systems combined with combined heat and power (CHP) have an energy conversion efficiency of 70–80% or higher than conventional combustion methods.

[0003] The single cell, which is the core of such an SOFC, consists of a cathode, an electrolyte, and an anode, and in the case of a typical single cell, the cathode accounts for about 50% of the total polarization resistance of the unit cell.

[0004] Overvoltage at the air electrode is the biggest factor in the reduction of overall SOFC performance, and it can be seen that the air electrode determines the performance of not only SOFC single cells but also SOFC stacks.

[0005] Meanwhile, perovskite generally refers to a series of inorganic materials having an ABO3 crystal structure, where rare earth metals (e.g., La, Sm, etc.) or alkaline earth metals (Ba, Sr, etc.) can be substituted at the A position, and transition metals (Co, Fe, Mn, etc.) can be substituted at the B position. Through this substitution process, the electronic structure and the degree of oxygen vacancy can be controlled, making it possible to adjust electrical conductivity, catalytic activity, and thermal stability in various ways. In particular, since the electronic structure is closely related to the d-electron or p-electron band, examples showing changes in electrical conductivity depending on temperature and oxygen partial pressure (pO2) are widely reported.

[0006] Generally, when perovskite materials are repeatedly exposed to environments with fluctuating oxygen partial pressures at high temperatures, a phenomenon of accumulating changes in electrical conductivity may occur. While changes in electrical conductivity due to oxygen injection and deoxygenation initially appear to be reversible, it has been reported that as thermal cycling increases, irreversible structural changes or degradation accumulate, making it difficult to fully recover conductivity. This is because localized oxidation and reduction reactions occur repeatedly within the material, leading to the formation of non-uniform deficiencies and defects near grain boundaries or interfaces.

[0007] To overcome these problems, previous attempts have been made to balance oxygen ion mobility and electronic conductivity by controlling the content of transition metals such as Co and Mn in various perovskite compositions, or by substituting rare earth metals (such as La and Sm) with Ba and Sr. Additionally, experiments have been conducted to control the oxygen deficiency (δ) of the material by varying the heat treatment temperature, atmosphere, and time. However, these attempts generally showed limitations, such as material properties being maximized only when the oxygen atmosphere was maintained constantly for a long period, or electrical conductivity appearing stably only when the range of temperature fluctuations was small.

[0008] For example, it was observed that while some Ruddlesden-Popper structures exhibit excellent oxygen ion conductivity within a specific temperature range, oxygen deficiency rapidly increases under prolonged low-oxygen conditions, leading to an irreversible fixation of this state and a loss of conductivity. Similarly, there have been cases where repeated thermal cycling in an inert gas atmosphere has induced heterogeneous phase separation on the surface or within the material, resulting in a significant decrease in the overall electrical conductivity of the material.

[0009] It is known that in real-world environments where oxygen partial pressure fluctuations or thermal cycling occur frequently (e.g., power plant fuel cells, process furnaces, automotive exhaust sensors, etc.), maintaining stable electrical conductivity during high-temperature operation requires characteristics that prevent excessive oxygen deficiency even when oxygen partial pressure temporarily decreases, and enable the material to recover its original electrical conductivity level within a relatively short time when oxygen is supplied again. In this regard, material structures or compositions that prevent the accumulation of degradation are required; however, it is reported that there are currently not many layered perovskites that operate stably for a long period under repeated high-temperature and low-oxygen conditions.

[0010] Meanwhile, Korean Registered Patent Publication No. 10-1963980 is presented as a similar prior art document regarding this. Prior art literature

[0011] Korean Patent Publication No. 10-1963980 (March 25, 2019) The problem to be solved

[0012] To solve the above-mentioned problems, the present invention aims to provide a non-stoichiometric layered perovskite in which electrical conductivity is reversibly recovered when the temperature is repeatedly raised and lowered within a predetermined temperature range between an oxygen and a non-oxygen atmosphere, and a method for recovering the electrical conductivity thereof.

[0013] However, the above purpose is exemplary, and the technical concept of the present invention is not limited thereto. means of solving the problem

[0014] One embodiment of the present invention for achieving the above objective relates to a non-stoichiometric layered perovskite satisfying the following chemical formula 1, wherein the non-stoichiometric layered perovskite is characterized in that its electrical conductivity is restored to satisfy the following relationship 1.

[0015] [Chemical Formula 1]

[0016] La1A1 x A 2 y (B a Fe 1-a ) z O 5+δ

[0017] (In the above chemical formula 1,

[0018] La is a lanthanide element, and A 1 Department A 2 is a different alkaline earth metal element, and B is a transition metal element excluding Fe;

[0019] x is a real number satisfying 0.1 < x < 0.9, y is a real number satisfying 0.1 < y < 0.9, and z is a real number satisfying 1.5 < z < 2.5, provided that x=0.5, y=0.5, and z=2 are not simultaneously satisfied;

[0020] a is a real number satisfying 0.01 ≤ a ≤ 0.99;

[0021] δ is a real number satisfying 0 < δ ≤ 0.5.

[0022] [Relationship 1]

[0023] 60 ≤ (σ n+1 / σ O )×100

[0024] (In the above relationship 1,

[0025] σ O is the electrical conductivity value (S / cm) at 50℃ after one cycle of heating and cooling within a predetermined temperature range in an oxygen atmosphere, and

[0026] σ n+1 is the electrical conductivity value (S / cm) at 50℃ after n cycles of heating and cooling within a predetermined temperature range in a non-oxygen atmosphere, and n+1 cycles of heating and cooling within a predetermined temperature range in an oxygen atmosphere, where n is an even number greater than or equal to 2.

[0027] In one embodiment above, La may be lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or ruthenium (Lu), and more preferably, La may be samarium (Sm).

[0028] In the above-mentioned embodiment, the above A 1 and A 2 may independently be barium (Ba), strontium (Sr), calcium (Ca), or magnesium (Mg), and more preferably, the above A 1 It is barium (Ba), and the above A 2 It can be strontium (Sr).

[0029] In one embodiment above, B may be cobalt (Co), platinum (Pt), zinc (Zn), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), or nickel (Ni), and more preferably, B may be cobalt (Co).

[0030] In the above embodiment, the perovskite oxide of the above non-stoichiometric composition may satisfy the following chemical formula 2.

[0031] [Chemical Formula 2]

[0032] Sm1Ba x Sr y (Co a Fe 1-a ) z O 5+δ

[0033] (In the above chemical formula 2,

[0034] x is a real number satisfying 0.1 < x ≤ 0.5, y is a real number satisfying 0.1 < y ≤ 0.5, and z is a real number satisfying 1.5 < z < 2.5, provided that x=0.5, y=0.5, and z=2 are not simultaneously satisfied;

[0035] a is a real number satisfying 0.1 ≤ a ≤ 0.9;

[0036] δ is a real number satisfying 0 < δ ≤ 0.5.

[0037] In the above embodiment, a may be a real number satisfying 0.3 ≤ a ≤ 0.8.

[0038] In the above embodiment, the oxygen-free atmosphere may be an inert gas atmosphere.

[0039] In addition, another aspect of the present invention comprises: a) a step of raising and lowering the temperature of a non-stoichiometric layered perovskite satisfying the following chemical formula 1 by one step to a predetermined temperature range in an oxygen atmosphere; b) a step of raising and lowering the temperature n (where n is an even number greater than or equal to 2) times to a predetermined temperature range in a non-oxygen atmosphere; and c) a step of raising and lowering the temperature n+1 times to a predetermined temperature range in an oxygen atmosphere; and

[0040] Steps b) and c) above are repeated one or more times, and

[0041] The present invention relates to a method for recovering the electrical conductivity of a non-stoichiometric layered perovskite, characterized in that the electrical conductivity of the non-stoichiometric layered perovskite is recovered to satisfy the following relationship 1.

[0042] [Chemical Formula 1]

[0043] La1A 1 x A 2 y (B a Fe 1-a ) z O 5+δ

[0044] (In the above chemical formula 1,

[0045] La is a lanthanide element, and A 1 Department A 2 is a different alkaline earth metal element, and B is a transition metal element excluding Fe;

[0046] x is a real number satisfying 0.1 < x < 0.9, y is a real number satisfying 0.1 < y < 0.9, and z is a real number satisfying 1.5 < z < 2.5, provided that x=0.5, y=0.5, and z=2 are not simultaneously satisfied;

[0047] a is a real number satisfying 0.01 ≤ a ≤ 0.99;

[0048] δ is a real number satisfying 0 < δ ≤ 0.5.

[0049] [Relationship 1]

[0050] 60 ≤ (σ n+1 / σ O )×100

[0051] (In the above relationship 1,

[0052] σ O is the electrical conductivity value (S / cm) at 50℃ after one cycle of heating and cooling within a predetermined temperature range in an oxygen atmosphere, and

[0053] σ n+1 is the electrical conductivity value (S / cm) at 50℃ after n cycles of heating and cooling within a predetermined temperature range in a non-oxygen atmosphere, and n+1 cycles of heating and cooling within a predetermined temperature range in an oxygen atmosphere, where n is an even number greater than or equal to 2. Effects of the invention

[0054] The non-stoichiometric layered perovskite according to the present invention has a non-stoichiometric composition satisfying Formula 1, and thus can exhibit reversible electrical conductivity characteristics in which electrical conductivity is reversibly recovered when repeatedly raised and lowered within a predetermined temperature range between oxygen and non-oxygen atmospheres. This means that irreversible degradation is minimized by controlling the excessive accumulation of oxygen deficiency within the material, and furthermore, operating costs and device complexity can be reduced in various application fields such as solid oxide fuel cells (SOFC), mobile fuel cells, power generation fuel cells, solid oxide water electrolysis cells, high-temperature gas sensors, and catalytic reactor components. In addition, the metal-insulator transition (MIT) behavior occurring around 300°C is also stably maintained under repeated thermal cycling conditions, allowing the electronic and ionic properties of the material to be secured for a long period. Ultimately, the non-stoichiometric layered perovskite according to the present invention can provide high durability and excellent performance even in environments where oxygen partial pressure and thermal fluctuations are frequent. Brief explanation of the drawing

[0055] Figure 1 is a graph showing the electrical conductivity measurement results of SBSCF 2.05-0.3 as the temperature rises and falls in an oxygen or nitrogen atmosphere. Figure 2 is a graph showing the electrical conductivity measurement results of SBSCF 2.05-0.5 as the temperature rises and falls in an oxygen or nitrogen atmosphere. Figure 3 is a graph showing the electrical conductivity measurement results of SBSCF 2.05-0.7 as the temperature rises and falls in an oxygen or nitrogen atmosphere. Specific details for implementing the invention

[0056] The non-stoichiometric layered perovskite according to the present invention and the method for recovering its electrical conductivity are described in detail below. The drawings presented below are provided as examples to ensure that the concept of the present invention is sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the concept of the present invention. Unless otherwise defined, technical and scientific terms used herewith have the meanings commonly understood by those skilled in the art to which this invention pertains, and descriptions of known functions and configurations that could unnecessarily obscure the essence of the present invention are omitted in the following description and accompanying drawings.

[0057] One embodiment of the present invention relates to a non-stoichiometric layered perovskite satisfying the following chemical formula 1, wherein the non-stoichiometric layered perovskite is characterized in that its electrical conductivity is restored to satisfy the following relationship 1.

[0058] [Chemical Formula 1]

[0059] La1A 1 x A 2 y (B a Fe 1-a ) z O 5+δ

[0060] (In the above chemical formula 1,

[0061] La is a lanthanide element, and A 1 Department A 2 is a different alkaline earth metal element, and B is a transition metal element excluding Fe;

[0062] x is a real number satisfying 0.1 < x < 0.9, y is a real number satisfying 0.1 < y < 0.9, and z is a real number satisfying 1.5 < z < 2.5, provided that x=0.5, y=0.5, and z=2 are not simultaneously satisfied;

[0063] a is a real number satisfying 0.01 ≤ a ≤ 0.99;

[0064] δ is a real number satisfying 0 < δ ≤ 0.5.

[0065] [Relationship 1]

[0066] 60 ≤ (σ n+1 / σ O )×100

[0067] (In the above relationship 1,

[0068] σ O is the electrical conductivity value (S / cm) at 50℃ after one cycle of heating and cooling within a predetermined temperature range in an oxygen atmosphere, and

[0069] σ n+1 is the electrical conductivity value (S / cm) at 50℃ after n cycles of heating and cooling within a predetermined temperature range in a non-oxygen atmosphere, and n+1 cycles of heating and cooling within a predetermined temperature range in an oxygen atmosphere, where n is an even number greater than or equal to 2.

[0070] As such, the non-stoichiometric layered perovskite according to the present invention has a non-stoichiometric composition satisfying Formula 1, and thus can exhibit reversible electrical conductivity characteristics in which electrical conductivity is reversibly recovered when repeatedly raised and lowered within a predetermined temperature range between oxygen and non-oxygen atmospheres. This means that irreversible degradation is minimized by controlling the excessive accumulation of oxygen deficiency within the material, and furthermore, it enables the reduction of operating costs and device complexity in various application fields such as solid oxide fuel cells (SOFC), mobile fuel cells, power generation fuel cells, solid oxide water electrolysis cells, high-temperature gas sensors, and catalytic reactor components. In addition, the metal-insulator transition (MIT) behavior occurring around 300°C is also stably maintained under repeated thermal cycling conditions, allowing the electronic and ionic properties of the material to be secured for a long period, and ultimately, the non-stoichiometric layered perovskite according to the present invention can provide high durability and excellent performance even in environments where oxygen partial pressure and thermal fluctuations are frequent.

[0071] Hereinafter, a non-stoichiometric layered perovskite according to an example of the present invention will be described in more detail.

[0072] First, a layered perovskite of non-stoichiometric composition according to one example of the present invention may satisfy the formula 1 above. A layered perovskite of non-stoichiometric composition satisfying this may exhibit reversible electrical conductivity characteristics in which electrical conductivity is reversibly recovered when the temperature is repeatedly raised and lowered within a predetermined temperature range between an oxygen and non-oxygen atmosphere.

[0073] As a more specific example, in the above Chemical Formula 1, La may be lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), or ruthenium (Lu), and more preferably may be samarium (Sm). The above A 1 and A 2 may independently be barium (Ba), strontium (Sr), calcium (Ca), or magnesium (Mg), and more preferably, the above A 1 It is barium (Ba), and the above A 2 B may be strontium (Sr). B may be cobalt (Co), platinum (Pt), zinc (Zn), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), or nickel (Ni), and more preferably may be cobalt (Co).

[0074] At this time, δ in Chemical Formula 1 may represent interstitial oxygen, and by including it, the conductivity of oxygen ions may be improved. As a specific example, δ may have a value greater than 0 and less than or equal to 0.5, but is not limited thereto, and the value of δ may be determined according to the specific crystal structure.

[0075] As a more desirable example, the perovskite oxide of the above non-stoichiometric composition may satisfy the following chemical formula 2.

[0076] [Chemical Formula 2]

[0077] Sm1Ba x Sr y (Co a Fe 1-a ) z O 5+δ

[0078] (In the above chemical formula 2,

[0079] x is a real number satisfying 0.1 < x ≤ 0.5, y is a real number satisfying 0.1 < y ≤ 0.5, and z is a real number satisfying 1.5 < z < 2.5, provided that x=0.5, y=0.5, and z=2 are not simultaneously satisfied;

[0080] a is a real number satisfying 0.1 ≤ a ≤ 0.9;

[0081] δ is a real number satisfying 0 < δ ≤ 0.5.

[0082] In particular, the ability to recover reversible electrical conductivity may vary depending on the ratio of Fe, and more preferably, the above a may be a real number satisfying 0.3 ≤ a ≤ 0.8, and even more preferably, a may be a real number satisfying 0.3 ≤ a ≤ 0.5. Within such a range, reversible electrical conductivity characteristics can be effectively exhibited, in which electrical conductivity is reversibly recovered when repeatedly raised and lowered within a predetermined temperature range between an oxygen and non-oxygen atmosphere.

[0083] In addition, in the above chemical formula 2, x is a real number satisfying 0.4 < x ≤ 0.5, y is a real number satisfying 0.4 < x ≤ 0.5, z is a real number satisfying 2 < x < 2.5; and δ may be a real number satisfying 0 < δ ≤ 0.5. When these conditions are satisfied, higher electrical conductivity characteristics can be secured.

[0084] Meanwhile, Equation 1 represents the reversible electrical conductivity characteristics, preferably (σ n+1 / σ O )×100 can be 80 or more, and more preferably 90 or more. At this time, the predetermined temperature range in Equation 1 is not specifically limited but can be 50 to 900°C, and the non-oxygen atmosphere can be an inert gas atmosphere such as nitrogen, argon, or helium.

[0085] In addition, another aspect of the present invention relates to a method for recovering electrical conductivity using the aforementioned non-stoichiometric layered perovskite, and more specifically, comprises: a) a step of raising and lowering the temperature of a non-stoichiometric layered perovskite satisfying the following chemical formula 1 by one step to a predetermined temperature range in an oxygen atmosphere; b) a step of raising and lowering the temperature n (where n is an even number greater than or equal to 2) times to a predetermined temperature range in a non-oxygen atmosphere; and c) a step of raising and lowering the temperature n+1 times to a predetermined temperature range in an oxygen atmosphere; and

[0086] Steps b) and c) above are repeated one or more times, and

[0087] The present invention relates to a method for recovering the electrical conductivity of a non-stoichiometric layered perovskite, characterized in that the electrical conductivity of the non-stoichiometric layered perovskite is recovered to satisfy the following relationship 1.

[0088] [Chemical Formula 1]

[0089] La1A 1 x A 2 y (B a Fe 1-a ) z O 5+δ

[0090] (In the above chemical formula 1,

[0091] La is a lanthanide element, and A 1 Department A 2 is a different alkaline earth metal element, and B is a transition metal element excluding Fe;

[0092] x is a real number satisfying 0.1 < x < 0.9, y is a real number satisfying 0.1 < y < 0.9, and z is a real number satisfying 1.5 < z < 2.5, provided that x=0.5, y=0.5, and z=2 are not simultaneously satisfied;

[0093] a is a real number satisfying 0.01 ≤ a ≤ 0.99;

[0094] δ is a real number satisfying 0 < δ ≤ 0.5.

[0095] [Relationship 1]

[0096] 80 ≤ (σ n+1 / σ O )×100

[0097] (In the above relationship 1,

[0098] σ O is the electrical conductivity value (S / cm) at 50℃ after one cycle of heating and cooling within a predetermined temperature range in an oxygen atmosphere, and

[0099] σ n+1 is the electrical conductivity value (S / cm) at 50℃ after n cycles of heating and cooling within a predetermined temperature range in a non-oxygen atmosphere, and n+1 cycles of heating and cooling within a predetermined temperature range in an oxygen atmosphere, where n is an even number greater than or equal to 2.

[0100] At this time, since Chemical Formula 1 and Relationship 1 are the same as those previously described, a redundant explanation is omitted.

[0101] First, when a non-stoichiometric layered perovskite satisfying Chemical Formula 1 is prepared, a step of raising and lowering the temperature once within a predetermined temperature range in an oxygen atmosphere can be performed. Referring to FIGS. 1 to 3, the non-stoichiometric layered perovskite satisfying Chemical Formula 1 may exhibit Metal-Insulator transition (MIT) behavior in which the electrical conductivity increases as the temperature increases at temperatures below 300°C, and decreases as the temperature increases at high temperatures above 300°C.

[0102] After the first temperature increase and decrease, b) a step of increasing and decreasing the temperature n times (where n is an even number greater than or equal to 2) times within a predetermined temperature range in a non-oxygen atmosphere may be performed. Referring to FIGS. 1 to 3, the non-stoichiometric layered perovskite satisfying Chemical Formula 1 may be a p-type conductor in which the electrical conductivity value in an even number of times in a non-oxygen atmosphere is lower than in an oxygen atmosphere, and the electrical conductivity decreases at low oxygen partial pressure.

[0103] Subsequently, step c) of raising and lowering the temperature n+1 times within a predetermined temperature range in an oxygen atmosphere can be performed again. Referring to FIGS. 1 to 3, a non-stoichiometric layered perovskite whose electrical conductivity has dropped sharply after lowering in a non-oxygen atmosphere can recover electrical conductivity similar to that of the first time by rapidly increasing the electrical conductivity when raised again in an oxygen atmosphere, and thus the non-stoichiometric layered perovskite of the present invention can have reversible electrical conductivity characteristics.

[0104] At this time, steps b) and c) above may be repeated one or more times, and specifically, for example, n may be an even number such as 2, 4, 6, 8, 10, and n+1 may be an odd number such as 3, 5, 7, 9, 11.

[0105] Meanwhile, the predetermined temperature range during the 1st, nth, and n+1th heating and cooling cycles is not specifically limited, but may be 50 to 900℃.

[0107] Hereinafter, the non-stoichiometric layered perovskite according to the present invention and the method for recovering its electrical conductivity will be described in more detail through examples. However, the following examples are merely references for explaining the present invention in detail, and the present invention is not limited thereto and can be implemented in various forms.

[0108] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as generally understood by one of the art to which the present invention pertains. The terms used in the description herein are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention. Additionally, units of additives not specifically stated in the specification may be in weight percent.

[0109] [Preparation Examples 1 to 3]

[0110] Air electrode powder was prepared using a solid-state reaction. Specifically, for accurate experiments, reagent-grade Sm2O3, BaCO3, SrCO3, Co3O4, and Fe3O4 were heat-treated in an electric furnace at 150°C for 1 hour to remove moisture, and then weighed accurately according to the composition of the layered perovskite to be prepared. The composition of each layered perovskite is shown in Table 1 below.

[0111] Each weighed powder was mixed with an ethanol solvent via ball milling to produce air electrode powder, and then heat-treated at 1000°C for 6 hours and at 1100°C for 8 hours in an air atmosphere to prepare layered perovskite.

[0112] furtherance abbreviation Preparation Example 1 SmBa 0.5 Sr 0.48 (Co 0.3 Feb 0.7 ) 2.05 O 5+δ SBSCF 2.05-0.3 Preparation Example 2 SmBa 0.5 Sr 0.48 (Co 0.5 Feb 0.5 ) 2.05 O 5+δ SBSCF 2.05-0.5 Preparation Example 3 SmBa 0.5 Sr 0.48 (Co 0.7 Feb 0.3 ) 2.05 O 5+δ SBSCF 2.05-0.7

[0113] [Examples 1 to 3]

[0114] The specimens for measuring electrical conductivity are 1.8 x 10⁻⁶ in the powder of each composition 3 kg / m 2Compression molding was performed by applying pressure. The compressed powder was heat-treated in an air atmosphere at 1100°C for 3 hours to produce a bar-type sample with a dense structure. Electrical conductivity was measured using the DC 4-probe method. The DC 4-probe method is a method of measuring electrical conductivity using four wires by applying voltage to two wires connected to the center of the specimen and applying current to two wires connected to both ends.

[0115] Electrical conductivity measurements were conducted in a total of six repeated experiments, from cycle 1 to cycle 6. Each cycle included a process of raising the temperature from 50°C to 900°C and then lowering it back down from 900°C to 50°C, with the temperature adjusted in 50°C increments. Cycles 1, 3, and 5 were conducted in an air atmosphere, while cycles 2, 4, and 6 were conducted in a nitrogen atmosphere, thereby observing electrical conductivity according to changes in oxygen partial pressure. Electrical conductivity was measured by applying currents of 0.1 A, 0.5 A, and 1.0 A for each temperature, and the changes in electrical conductivity occurring during the repeated switching between air and nitrogen atmospheres were analyzed.

[0116] The above method for measuring changes in electrical conductivity is briefly shown in Table 2 below.

[0117] Episode Oxygen partial pressure Applied current temperature 1st round Air atmosphere 0.1 A / 0.5 A / 1.0 A Temperature increase 50 → 900℃ / Temperature decrease 900 → 50℃ 3rd round 5th session 2nd round nitrogen atmosphere 4th round 6th round

[0118] [Characteristics Evaluation]

[0119] Figure 1 is a graph showing the electrical conductivity measurement results of SBSCF 2.05-0.3 as a function of temperature. It exhibited Metal-Insulator transition (MIT) behavior, in which the electrical conductivity increased with increasing temperature at temperatures below 300℃ during up and down heating, and decreased with increasing temperature at high temperatures above 300℃.

[0120] In addition, the electrical conductivity values ​​in the air atmosphere of the 1st, 3rd, and 5th trials were higher than the electrical conductivity values ​​in the nitrogen atmosphere of the 2nd, 4th, and 6th trials, which confirmed that it is a p-type conductor whose electrical conductivity decreases at low oxygen partial pressure.

[0121] During the second heating cycle, the electrical conductivity decreased by about 2.5 times compared to when the temperature was raised from 300℃, but during the third heating cycle, the electrical conductivity recovered to a level similar to the value from the first cycle at around 300℃.

[0122] These electrical conductivity characteristics were observed identically in subsequent trials, and through this, it was confirmed that SBSCF 2.05-0.3 has reversible electrical conductivity, with electrical conductivity recovering at around 300°C even with repeated changes in oxygen partial pressure.

[0123] Figure 2 is a graph showing the electrical conductivity measurement results of SBSCF 2.05-0.5 as a function of temperature, exhibiting Metal-Insulator transition (MIT) behavior in which the electrical conductivity increases with increasing temperature at temperatures below 300℃ during up and down heating, and decreases with increasing temperature at high temperatures above 300℃.

[0124] In addition, the electrical conductivity values ​​in the air atmosphere of the 1st, 3rd, and 5th trials were higher than the electrical conductivity values ​​in the nitrogen atmosphere of the 2nd, 4th, and 6th trials, which confirmed that it is a p-type conductor whose electrical conductivity decreases at low oxygen partial pressure.

[0125] During the second heating cycle, the electrical conductivity decreased by about 1.5 times compared to when the temperature was raised from 300℃, but during the third heating cycle, the electrical conductivity recovered to a level similar to the value from the first cycle at around 300℃.

[0126] These electrical conductivity characteristics were observed identically in subsequent trials, and through this, it was confirmed that SBSCF 2.05-0.5 has reversible electrical conductivity, with electrical conductivity recovering at around 300°C even with repeated changes in oxygen partial pressure.

[0127] Figure 3 is a graph showing the results of measuring the electrical conductivity of SBSCF 2.05-0.7 according to temperature. It exhibited Metal-Insulator transition (MIT) behavior, in which the electrical conductivity increased with increasing temperature at temperatures below 300°C and decreased with increasing temperature at high temperatures above 300°C. On the other hand, unlike SBSCF 2.05-0.3 and SBSCF 2.05-0.5, the same MIT behavior as in an air atmosphere was observed during the second cooling cycle in a nitrogen atmosphere, but semiconductor behavior was observed in which the electrical conductivity increased with increasing temperature when the temperature was lowered during the fourth and sixth cooling cycles.

[0128] In addition, the electrical conductivity values ​​in the air atmosphere of the 1st, 3rd, and 5th trials were higher than the electrical conductivity values ​​in the nitrogen atmosphere of the 2nd, 4th, and 6th trials, which confirmed that it is a p-type conductor whose electrical conductivity decreases at low oxygen partial pressure.

[0129] During the second heating cycle, the electrical conductivity decreased by about 1.2 times compared to when the temperature was raised from 300℃, but during the third heating cycle, the electrical conductivity recovered to a level similar to the value from the first cycle at around 300℃.

[0130] These electrical conductivity characteristics were observed identically in subsequent cycles, and through this, it was confirmed that SBSCF 2.05-0.7 has reversible electrical conductivity, with electrical conductivity recovering at around 300°C even with repeated changes in oxygen partial pressure.

[0131] In particular, SBSCF 2.05-0.7, which had the highest amount of Fe substitution, showed the smallest difference in electrical conductivity between air (cycles 1, 3, 5) and nitrogen (cycles 2, 4, 6), which allowed us to conclude that the difference in electrical conductivity values ​​according to oxygen partial pressure decreases as the amount of Fe substitution increases.

[0132] Meanwhile, the electrical conductivity values ​​(S / cm) at 50℃ after rising and falling for SBSCF 2.05-0.3, SBSCF 2.05-0.5, and SBSCF 2.05-0.7 are shown in Table 3 below.

[0133] σ [S / cm], at 50℃(down) SBSCF 2.05-0.3 SBSCF 2.05-0.5 SBSCF 2.05-0.7 1st round 217.45 39.07 6.30 2nd round 50.35 4.87 0.13 3rd round 250.76 37.36 5.34 4th round 183.27 19.61 0.12 5th session 286.82 36.15 4.27 6th round 100.57 13.36 2.14

[0134] Referring to Table 3 above, even though the electrical conductivity of the corresponding part at 50°C in the 2nd, 4th, and 6th trials decreased by 2 to 10 times compared to the 1st, 3rd, and 5th trials, when an oxygen atmosphere was created again, there was almost no difference from the electrical conductivity in the oxygen atmosphere of the 1st trial. There was a very slight difference of about 1.5 times between the electrical conductivity of the 1st trial and the electrical conductivity of the 3rd and 5th trials, and in the case of SBSCF 2.05-0.3, the electrical conductivity increased.

[0135] Although the present invention has been described above through specific details and limited embodiments, this is provided merely to aid in a more comprehensive understanding of the invention, and the invention is not limited to the above embodiments. Those skilled in the art can make various modifications and variations from this description.

[0136] Accordingly, the scope of the present invention is not limited to the described embodiments, and all things equivalent to or having equivalent variations to the claims set forth below, as well as the claims set forth below, shall be considered to fall within the scope of the concept of the present invention.

Claims

Claim 1 A non-stoichiometric layered perovskite satisfying the following chemical formula 2, wherein the non-stoichiometric layered perovskite is characterized by having its electrical conductivity restored to satisfy the following relationship 1. [Chemical Formula 2] Sm1Ba x Sr y (Co a Fe 1-a ) z O 5+δ (In the above Chemical Formula 2, x is a real number satisfying 0.1 < x ≤ 0.5, y is a real number satisfying 0.1 < y ≤ 0.5, z is a real number satisfying 2 < z < 2.5; a is a real number satisfying 0.1 ≤ a ≤ 0.9; and δ is a real number satisfying 0 < δ ≤ 0.5.)[Relation 1] 60 ≤ (σ n+1 / σ O )×100(in the above relationship 1, σ O is the electrical conductivity value (S / cm) at 50°C after a first heating and cooling cycle in an oxygen atmosphere within a temperature range of 50 to 900°C, and σ n+1 is the electrical conductivity value (S / cm) at 50°C after n cycles of heating and cooling within a temperature range of 50 to 900°C in a non-oxygen atmosphere, and n+1 cycles of heating and cooling within a temperature range of 50 to 900°C in an oxygen atmosphere, where n is an even number greater than or equal to 2. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 A non-stoichiometric layered perovskite according to claim 1, wherein a is a real number satisfying 0.3 ≤ a ≤ 0.

8. Claim 10 A non-stoichiometric layered perovskite, wherein the oxygen-free atmosphere is an inert gas atmosphere in claim 1. Claim 11 a) a step of raising and lowering the temperature of a non-stoichiometric layered perovskite satisfying the following chemical formula 1 by one step within a predetermined temperature range in an oxygen atmosphere; b) a step of raising and lowering the temperature n (where n is an even number greater than or equal to 2) times within a predetermined temperature range in a non-oxygen atmosphere; and c) a step of raising and lowering the temperature n+1 times within a predetermined temperature range in an oxygen atmosphere; wherein steps b) and c) are repeated one or more times, and the electrical conductivity of the non-stoichiometric layered perovskite is restored to satisfy the following relationship 1. [Chemical Formula 1] La1A 1 x A 2 y (B a Fe 1-a ) z O 5+δ (In the above chemical formula 1, La is a lanthanide element, and A 1 Department A 2 and are different alkaline earth metal elements, and B is a transition metal element excluding Fe; x is a real number satisfying 0.1 < x < 0.9, y is a real number satisfying 0.1 < y < 0.9, and z is a real number satisfying 1.5 < z < 2.5, but not simultaneously satisfying x=0.5, y=0.5, and z=2; a is a real number satisfying 0.01 ≤ a ≤ 0.99; and δ is a real number satisfying 0 < δ ≤ 0.5.)[Equation 1] 60 ≤ (σ n+1 / σ O )×100(in the above relationship 1, σ O is the electrical conductivity value (S / cm) at 50℃ after one cycle of heating and cooling within a specified temperature range in an oxygen atmosphere, and σ n+1 is the electrical conductivity value (S / cm) at 50℃ after n cycles of heating and cooling within a predetermined temperature range in a non-oxygen atmosphere, and n+1 cycles of heating and cooling within a predetermined temperature range in an oxygen atmosphere, where n is an even number greater than or equal to 2. Claim 12 A method for restoring electrical conductivity of a non-stoichiometric layered perovskite, wherein La is lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or ruthenium (Lu). Claim 13 A method for restoring the electrical conductivity of a non-stoichiometric layered perovskite, wherein, in Clause 12, La is samarium (Sm). Claim 14 In Clause 11, the above A 1 and A 2 A method for restoring electrical conductivity of non-stoichiometric layered perovskites, wherein each is independently barium (Ba), strontium (Sr), calcium (Ca), or magnesium (Mg). Claim 15 In Clause 14, the above A 1 It is barium (Ba), and the above A 2 A method for restoring electrical conductivity of a non-stoichiometric layered perovskite, in which strontium (Sr) is present. Claim 16 A method for restoring the electrical conductivity of a non-stoichiometric layered perovskite, wherein B is cobalt (Co), platinum (Pt), zinc (Zn), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), or nickel (Ni) in claim 11. Claim 17 A method for restoring the electrical conductivity of a non-stoichiometric layered perovskite, wherein B is cobalt (Co) in Clause 16. Claim 18 A method for recovering the electrical conductivity of a non-stoichiometric layered perovskite according to claim 11, wherein the perovskite oxide of the non-stoichiometric composition satisfies the following Chemical Formula 2. [Chemical Formula 2] Sm1Ba x Sr y (Co a Fe 1-a ) z O 5+δ (In the above Chemical Formula 2, x is a real number satisfying 0.1 < x ≤ 0.5, y is a real number satisfying 0.1 < y ≤ 0.5, and z is a real number satisfying 1.5 < z < 2.5, but not simultaneously satisfying x=0.5, y=0.5, and z=2; a is a real number satisfying 0.1 ≤ a ≤ 0.9; and δ is a real number satisfying 0 < δ ≤ 0.5.) Claim 19 A method for recovering the electrical conductivity of a non-stoichiometric layered perovskite, wherein, in claim 18, a is a real number satisfying 0.3 ≤ a ≤ 0.

8. Claim 20 A method for restoring the electrical conductivity of a non-stoichiometric layered perovskite, wherein, in claim 11, the above-mentioned oxygen-free atmosphere is an inert gas atmosphere.

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