Iron-based perovskite air electrode material, preparation method and application thereof

Abstract

The application discloses an iron-based perovskite air electrode material and a preparation method and application thereof, and belongs to the technical field of solid oxide batteries. a Sr b Ca c Pr d Bi e FeO 3‑δ , wherein a+b+c+d+e=1, and 0.15<=a<=0.25, 0.15<=b<=0.25, 0.15<=c<=0.25, 0.15<=d<=0.25, and 0.15<=e<=0.25; 0

Description

Technical Field

[0001] This invention belongs to the field of solid oxide battery technology, specifically relating to an iron-based perovskite air electrode material, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] In recent years, with the increasing depletion of fossil fuels and the aggravation of environmental pollution, the development of clean and efficient energy conversion technologies has become crucial. Solid oxide fuel cells (SOFCs) have attracted much attention due to their advantages such as high energy conversion efficiency, wide fuel adaptability, and environmental friendliness. However, traditional SOFCs require operation at high temperatures of 800-1000 °C, leading to material aging, shortened lifespan, and high costs. Lowering the operating temperature to the medium-low temperature range (600-800 °C) significantly slows down the oxygen reduction reaction (ORR) kinetics at the air electrode, causing a sharp increase in polarization resistance, which becomes a major bottleneck restricting battery performance.

[0004] High-entropy perovskite oxides, as novel single-phase solid solutions containing five or more elements, have shown potential as high-performance air electrode materials due to their high-entropy effect, lattice distortion, and cocktail effect. However, existing high-entropy air electrode materials still suffer from insufficient ORR activity at medium and low temperatures, poor interfacial compatibility with different electrolytes (such as oxygen ion conductors and proton conductors), and the need to verify their long-term stability under actual operating conditions containing CO2 and hydrogen. For example, the recently disclosed high-entropy perovskite material K... 0.4 Ba 0.2 Sr 0.2 Pr 0.2 La 0.2 FeO 3-δ Although (CN118983452A) employs a high-entropy design, it contains an alkali metal element at the A-site. Its background section explicitly acknowledges that "due to the diversity of elements, even slight modifications will increase the complexity of the crystal structure," and it does not provide long-term stability test data. Another example is Ruddlesden–Popper iron-based perovskite Sr3Fe2O. 7-δ When used as an air electrode material, excessive proton absorption under reversible operating conditions leads to crystal structure degradation, severely impacting battery durability. Therefore, developing a novel air electrode material with high catalytic activity, excellent compatibility, and dual-mode stability is crucial for promoting the commercialization of reversible solid oxide batteries (RSOCs). Summary of the Invention

[0005] This invention addresses the technical problems of insufficient catalytic activity, poor chemical compatibility, and poor stability of existing solid oxide battery air electrode materials under medium and low temperature conditions, and provides an iron-based perovskite air electrode material, its preparation method, and its applications.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides an iron-based perovskite air electrode material with the general chemical formula Ba. a Sr b Ca c Pr d Bi e FeO 3-δ , where a+b+c+d+e=1, and a, b, c, d, and e are all greater than 0; δ is the oxygen vacancy content, 0<δ<1.

[0007] Furthermore, 0.15≤a≤0.25, 0.15≤b≤0.25, 0.15≤c≤0.25, 0.15≤d≤0.25, and 0.15≤e≤0.25.

[0008] Preferably, when a=b=c=d=e=0.2, the molecular formula of the material is (BaSrCaPrBi). 0.2 FeO 3-δ .

[0009] Furthermore, the material has a cubic perovskite structure with a space group of Pm-3m.

[0010] This invention provides a method for preparing the above-mentioned iron-based perovskite air electrode material, comprising the following steps: (1) Weigh out metal oxides or carbonate precursors containing Ba, Sr, Ca, Pr, Bi and Fe according to the stoichiometric ratio of the general chemical formula, and mix them evenly.

[0011] (2) Add the mixed powder and grinding media (such as anhydrous ethanol) into a ball mill jar and ball mill at a speed of 300-500 r / min for 6-15 h. Dry the slurry obtained from ball milling and remove the solvent.

[0012] (3) After grinding the dried powder, pre-calcine it in air at a temperature of 700-900 ℃ for 5-15 h. The purpose of pre-calcine is to decompose the carbonate precursor into the corresponding oxide and initiate a solid-phase reaction to form the perovskite phase precursor. After pre-calcine, cool the powder to room temperature in the furnace. Take out the pre-calcine product, add a small amount of anhydrous ethanol as a grinding aid in a mortar, and grind it thoroughly again for 20-30 minutes to increase the specific surface area and reactivity of the powder.

[0013] (4) The pre-calcined product is thoroughly ground and then subjected to high-temperature final calcination in air atmosphere at a temperature of 1000-1200 °C for 3-10 h to obtain the iron-based high-entropy air electrode material. During this high-temperature stage, sufficient solid-phase reaction occurs between the oxides, ultimately forming the target product with a cubic perovskite structure. The final calcination temperature is a key process parameter that determines the phase purity, crystallinity, and microstructure of the product. Too low a temperature (<1000 °C) may lead to incomplete reaction and the presence of impurity phases; too high a temperature (>1200 °C) may lead to element volatilization or abnormal grain growth. After the final calcination is completed, the product is cooled to room temperature in the furnace, removed, and then gently ground and dispersed in an agate mortar and passed through a 200-mesh sieve to obtain the iron-based perovskite air electrode material.

[0014] Furthermore, in step (2), the ball milling speed is 400 r / min and the time is 10 h; in step (3), the drying temperature is 50-60 ℃ and the drying is carried out by magnetic stirring and heating.

[0015] This invention also provides the application of the above-mentioned iron-based perovskite air electrode material in the preparation of reversible solid oxide batteries.

[0016] Furthermore, the above-mentioned application method is as follows: the iron-based perovskite air electrode material is mixed with an organic binder and ground into a uniform slurry; then the slurry is coated on both sides of the electrolyte layer of the solid oxide battery, and after sintering, an air electrode layer is formed.

[0017] Furthermore, the organic binder is a mixture of ethyl cellulose and terpineol in a mass ratio of 9:1; the mass ratio of the air electrode material to the organic binder is 1:2.

[0018] Furthermore, the sintering conditions are: calcination at 1000-1100 ℃ for 3-5 h in an air atmosphere.

[0019] The beneficial effects of the technical solution provided by this invention are: 1. This invention introduces five elements—Ba, Sr, Ca, Pr, and Bi—at the A-site to form a high-entropy structure. Utilizing the high-entropy effect, lattice distortion, and cocktail effect, it significantly improves the oxygen vacancy concentration and oxygen transport capacity of the material. Experiments show that the polarization impedance of this material at 750 °C is as low as 0.5239 Ω·cm. 2 The peak power density reaches 0.39 W·cm³ in the 850 ℃ power generation mode. -2 It exhibits excellent ORR catalytic activity.

[0020] 2. The material provided by this invention not only exhibits excellent performance in SOFC power generation mode, but also demonstrates high catalytic activity in SOEC electrolysis mode. The current density reaches as high as 630 mA·cm⁻¹ at 850 °C and an electrolysis voltage of 1.3 V. -2 This indicates that it is an excellent dual-effect electrocatalyst, which is very suitable for use in reversible solid oxide batteries.

[0021] 3. This invention is prepared using a conventional solid-phase ball milling method, which is simple, easy to scale up for production, and does not contain precious metals or high-cost cobalt elements, which helps to reduce manufacturing costs. Attached Figure Description

[0022] Figure 1 (BaSrCaPrBi) prepared in Example 1 0.2 FeO 3-δ X-ray diffraction patterns of the material at different calcination temperatures; Figure 2 (BaSrCaPrBi) prepared in Example 1 0.2 FeO 3-δ Scanning electron microscope images of the material; Figure 3 (BaSrCaPrBi) prepared in Example 1 0.2 FeO 3-δ Elemental distribution diagram of the material in the energy dispersive X-ray spectrum; Figure 4 For (BaSrCaPrBi) 0.2 FeO 3-δ The AC impedance spectrum of the symmetrical cell with air electrode in the temperature range of 650-800 °C; Figure 5 For (BaSrCaPrBi) 0.2 FeO 3-δ AC impedance spectra of a single cell with an air electrode at different temperatures in power generation mode; Figure 6 For (BaSrCaPrBi) 0.2 FeO 3-δ The current density-voltage-power density curve of a single cell with an air electrode in power generation mode; Figure 7 For (BaSrCaPrBi) 0.2 FeO 3-δ AC impedance spectra of a single cell with an air electrode at different temperatures in electrolysis mode; Figure 8 For (BaSrCaPrBi) 0.2 FeO 3-δThe full characteristic IVP curve of a single cell with an air electrode in both power generation and electrolysis modes; Figure 9 For (BaSrCaPrBi) 0.2 FeO 3-δ Data on the long-term stability of the air electrode battery under CO2 and hydrogen atmospheres. Detailed Implementation

[0023] The specific embodiments of the present invention are described in detail below. These embodiments are intended to more fully demonstrate the technical content of the present invention and help to understand the specific implementation process of the present invention, but their content should not be construed as limiting the scope of the claims of the present invention in any way. For those skilled in the art, various adjustments, modifications, and substitutions made to the embodiments without departing from the spirit and scope of the present invention are all within the scope of protection sought by the present invention.

[0024] Example 1 (BaSrCaPrBi) 0.2 FeO 3-δ Preparation: Weigh out 3.9468 g of barium carbonate (BaCO3), 2.9526 g of strontium carbonate (SrCO3), 2.0018 g of calcium carbonate (CaCO3), and praseodymium oxide (Pr6O3). 11 3.4048 g of bismuth oxide (Bi2O3), 4.6596 g of bismuth oxide (Bi2O3), and 7.9845 g of iron oxide (Fe2O3).

[0025] The above raw materials were placed in a ball mill jar, and an appropriate amount of anhydrous ethanol was added as a medium. The mixture was ball milled at a speed of 300 r / min for 12 h.

[0026] Transfer the ball-milled slurry to a beaker, place it on a magnetic stirrer, and heat it at 50 °C while stirring until the ethanol is completely evaporated, resulting in a dry powder.

[0027] The dried powder was initially ground in a mortar and then calcined in a box furnace at 700 °C for 15 h in air. After removal, anhydrous ethanol was added, and the powder was ground thoroughly again. The ground powder was then placed back into the box furnace and calcined at 1200 °C for 3 h in air to finally obtain the target product (BaSrCaPrBi). 0.2 FeO 3-δ powder.

[0028] Example 2 Ba 0.25 Sr 0.15 Ca 0.2 Pr 0.25 Bi 0.15 FeO3-δ Preparation: Weigh out 4.9335 g of barium carbonate (BaCO3), 2.2145 g of strontium carbonate (SrCO3), 2.0018 g of calcium carbonate (CaCO3), and praseodymium oxide (Pr6O3). 11 4.2560 g of bismuth oxide (Bi2O3), 3.4947 g of bismuth oxide (Bi2O3), and 7.9845 g of iron oxide (Fe2O3).

[0029] The above raw materials were placed in a ball mill jar, and an appropriate amount of anhydrous ethanol was added as a medium. The mixture was ball-milled at a speed of 500 r / min for 6 h.

[0030] Transfer the ball-milled slurry to a beaker, place it on a magnetic stirrer, and heat it at 50 °C while stirring until the ethanol is completely evaporated, resulting in a dry powder.

[0031] The dried powder was initially ground in a mortar and then calcined in a box furnace at 900 °C for 12 h in air. After removal, anhydrous ethanol was added, and the powder was ground thoroughly again. The ground powder was then placed back into the box furnace and calcined at 1000 °C for 10 h in air to finally obtain the target product Ba. 0.25 Sr 0.15 Ca 0.2 Pr 0.25 Bi 0.15 FeO 3-δ powder.

[0032] Example 3 Ba 0.15 Sr 0.25 Ca 0.15 Pr 0.2 Bi 0.25 FeO 3-δ Preparation: Weigh out 2.9601 g of barium carbonate (BaCO3), 3.6908 g of strontium carbonate (SrCO3), 1.5014 g of calcium carbonate (CaCO3), and 1 g of praseodymium oxide (Pr6O3). 11 3.4084 g of bismuth oxide (Bi2O3), 5.8245 g of bismuth oxide (Bi2O3), and 7.9845 g of iron oxide (Fe2O3).

[0033] The above raw materials were placed in a ball mill jar, and an appropriate amount of anhydrous ethanol was added as a medium. The mixture was ball milled at a speed of 400 r / min for 10 h.

[0034] Transfer the ball-milled slurry to a beaker, place it on a magnetic stirrer, and heat it at 50 °C while stirring until the ethanol is completely evaporated, resulting in a dry powder.

[0035] The dried powder was initially ground in a mortar and then calcined in a box furnace at 800 °C for 15 h in air. After removal, anhydrous ethanol was added, and the powder was ground thoroughly again. The ground powder was then placed back into the box furnace and calcined at 1100 °C for 3 h in air to finally obtain the target product Ba. 0.15 Sr 0.25 Ca 0.15 Pr 0.2 Bi 0.25 FeO 3-δ powder.

[0036] Example 4 Ba 0.225 Sr 0.225 Ca 0.25 Pr 0.15 Bi 0.15 FeO 3-δ Preparation: Weigh out 4.4402 g of barium carbonate (BaCO3), 3.3218 g of strontium carbonate (SrCO3), 2.5023 g of calcium carbonate (CaCO3), and praseodymium oxide (Pr6O3). 11 2.5536 g of bismuth oxide (Bi2O3), 3.4947 g of bismuth oxide (Bi2O3), and 7.9845 g of iron oxide (Fe2O3).

[0037] The above raw materials were placed in a ball mill jar, and an appropriate amount of anhydrous ethanol was added as a medium. The mixture was ball milled at a speed of 400 r / min for 10 h.

[0038] Transfer the ball-milled slurry to a beaker, place it on a magnetic stirrer, and heat it at 50 °C while stirring until the ethanol is completely evaporated, resulting in a dry powder.

[0039] The dried powder was initially ground in a mortar and then calcined in a box furnace at 800 °C for 10 h in air. After removal, anhydrous ethanol was added, and the powder was ground thoroughly again. The ground powder was then placed back into the box furnace and calcined at 1200 °C for 5 h in air to finally obtain the target product Ba. 0.225 Sr 0.225 Ca 0.25 Pr 0.15 Bi 0.15 FeO 3-δ powder.

[0040] Example 5 Ba 0.25 Sr 0.15 Ca 0.25 Pr 0.15 Bi 0.2 FeO 3-δ Preparation: Weigh out 4.9335 g of barium carbonate (BaCO3), 2.2145 g of strontium carbonate (SrCO3), 2.5023 g of calcium carbonate (CaCO3), and praseodymium oxide (Pr6O3). 11 2.5536 g of bismuth oxide (Bi2O3), 4.6596 g of bismuth oxide (Bi2O3), and 7.9845 g of iron oxide (Fe2O3).

[0041] The above raw materials were placed in a ball mill jar, and an appropriate amount of anhydrous ethanol was added as a medium. The mixture was ball milled at a speed of 400 r / min for 10 h.

[0042] Transfer the ball-milled slurry to a beaker, place it on a magnetic stirrer, and heat it at 50 °C while stirring until the ethanol is completely evaporated, resulting in a dry powder.

[0043] The dried powder was initially ground in a mortar and then calcined in a box furnace at 800 °C for 10 h in air. After removal, anhydrous ethanol was added, and the powder was ground thoroughly again. The ground powder was then placed back into the box furnace and calcined at 1150 °C for 5 h in air to finally obtain the target product Ba. 0.25 Sr 0.15 Ca 0.25 Pr 0.15 Bi 0.2 FeO 3-δ powder.

[0044] Example 6 The (BaSrCaPrBi) prepared in Example 1 of this study... 0.2 FeO 3-δ The material and organic binder (ethyl cellulose: terpineol = 9:1) were mixed and ground at a mass ratio of 1:2 to prepare an air electrode slurry. The slurry was then coated onto Ce... 0.9 Gd 0.1 O 2-δ The two sides of the (GDC) electrolyte sheet are calcined at 1000 °C for 3 h in air atmosphere to make symmetrical cells or single cells for testing.

[0045] like Figure 1 As shown, the prepared material, after calcination at 1050 ℃, 1100 ℃, and 1150 ℃, yielded a single pure phase without any impurity peaks, indicating that the material has high phase purity and a cubic perovskite structure. Figure 2 It can be seen that the material particles are fine, uniformly distributed, and without obvious agglomeration. Less agglomeration helps to form more pores, thereby increasing the specific surface area of ​​the high-entropy material, which in turn increases the active sites of the electrode material and promotes improved electrochemical performance. Furthermore, from... Figure 3 The EDS results show that the elements Ba, Sr, Ca, Pr, Bi, Fe, and O are evenly distributed without segregation.

[0046] Electrochemical performance testing: by Figure 4 It can be seen that the polarization resistance of the air electrode material decreases with increasing test temperature. This is because the activity of the air electrode increases with increasing temperature, thus improving the catalytic performance of the ORR reaction. The polarization resistances of the symmetric cell using this material as the air electrode at 800 ℃, 750 ℃, 700 ℃, and 650 ℃ are 0.1094, 0.5239, 1.8268, and 5.9212 Ω·cm, respectively. 2 Compared to many other reported cobalt-based materials, (BaSrCaPrBi) 0.2 FeO3 exhibits low polarization resistance and excellent ORR kinetics. This is attributed to the multi-element synergistic effect generated by the complex coupling of multiple elements at the A-site and B-site, which optimizes the electronic structure, increases the internal oxygen vacancy concentration, enhances the oxygen transport capacity, and strengthens the catalytic activity of the oxygen reduction reaction. Elements such as Ba and Pr at the A-site promote oxygen ion diffusion, resulting in good ionic / electron mixed conductivity and thus lower polarization resistance. Preliminary results indicate that the high-entropy material (BaSrCaPrBi) exhibits... 0.2 FeO3 exhibits good electrochemical performance, with air electrode performance being even more superior.

[0047] Figure 5 As the operating temperature gradually increases from 700 °C to 850 °C, the diameter of the Nyquist curve decreases significantly, and the high-frequency intercept shifts to the left overall, indicating that the total impedance of the battery decreases substantially with increasing temperature. This is because the increase in temperature effectively lowers the activation energy of the oxygen reduction reaction in air, significantly accelerating the catalytic kinetics of oxygen molecule adsorption, dissociation, and charge transfer on the electrode surface, and increasing the diffusion rate of oxygen ions at the three-phase interface. Experimental results demonstrate that this material exhibits excellent electrochemical activity and low reaction resistance in the mid-to-high temperature range, significantly improving the output performance of solid oxide batteries. Figure 6 It can be seen that the open-circuit voltage of the single cell is around 1.1 V at all test temperatures, indicating that the electrolyte layer is dense and well-sealed. As the operating temperature increases, the slope of the IV curve gradually decreases, indicating a significant reduction in the total internal resistance of the battery, thereby resulting in a substantial increase in current density and power density; the peak power densities at 850 ℃, 800 ℃, 750 ℃, and 700 ℃ are 0.39 W. . cm -2 0.32W . cm -2 0.20W . cm -2 0.11W . cm -2 .

[0048] Figure 7 As can be seen from the impedance, as the operating temperature increases from 700 ℃ to 850 ℃, the curve shifts to the left and the arc diameter decreases significantly, indicating that the total impedance of the single cell in electrolysis mode decreases substantially with increasing temperature. The sharp reduction in the arc diameter reflects a significant decrease in polarization impedance. This is because the increase in temperature provides higher thermal energy for the electrolysis reaction, effectively lowering the energy barrier for interfacial charge transfer, accelerating the reaction kinetics, and thus significantly reducing activation polarization loss during electrolysis.

[0049] Figure 8 It can be seen that the current density at an electrolysis voltage of 1.3 V at 850 ℃, 800 ℃, 750 ℃, and 700 ℃ is 630 mA. . cm -2 455mA . cm -2 301mA . cm -2 and 173mA . cm -2 The main reason for the enhanced performance with increasing temperature in electrolysis mode is that high temperatures significantly accelerate the catalytic kinetics of the oxygen reduction and oxygen evolution reactions, effectively reducing the charge transfer energy barrier and simultaneously increasing the ion conduction rate within the electrolyte and electrodes. Experimental results demonstrate that this material, as a dual-effect electrocatalyst, exhibits excellent energy conversion efficiency and electrochemical stability in both power generation and electrolysis modes, making it suitable for high-performance reversible solid oxide batteries.

[0050] Depend on Figure 9 It can be seen that the battery operates at a constant current density of 100 mA. cm -2Under normal operating conditions, after 110 hours of continuous cyclic load testing, the battery output voltage remained highly stable, without significant voltage decay or increase in polarization overpotential, demonstrating the material's superior long-term service reliability. This excellent stability is mainly attributed to the following factors: First, the high-entropy perovskite crystal structure of this invention exhibits excellent thermodynamic stability, effectively suppressing the surface segregation of multi-component cations at A sites under high-temperature environments and strong electrochemical potential fields, ensuring the long-term stable existence of catalytic active sites on the electrode surface; Second, the material has good chemical compatibility with the GDC electrolyte. During long-term high-temperature service, there is no significant interdiffusion of elements at the electrode-electrolyte interface, and no high-resistivity secondary impurity phases are generated, maintaining stable interfacial contact resistance; Third, the material itself has excellent resistance to high-temperature sintering and good matching with the electrolyte's thermal expansion coefficient. During long-term thermal and electrochemical cycling, the porous microstructure of the electrode remains intact, and the three-phase reaction interface is not prone to shrinkage and degradation, effectively avoiding problems such as particle shedding and activity decay. In summary, the iron-based high-entropy perovskite air electrode material of this invention possesses both excellent low- and medium-temperature catalytic activity and long-term structural and interfacial stability, which can meet the application requirements of long-term stable operation under complex actual conditions of reversible solid oxide batteries.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An iron-based perovskite air electrode material, characterized in that, Its general chemical formula is Ba a Sr b Ca c Pr d Bi e FeO 3-δ , where a+b+c+d+e=1, and 0.15≤a≤0.25, 0.15≤b≤0.25, 0.15≤c≤0.25, 0.15≤d≤0.25, 0.15≤e≤0.25; δ is the oxygen vacancy content, 0<δ<1.

2. The iron-based perovskite air electrode material according to claim 1, characterized in that, The material has a cubic perovskite structure and a space group of Pm-3m.

3. A method for preparing the iron-based perovskite air electrode material according to any one of claims 1-2, characterized in that, The following steps are adopted: (1) Weigh the precursors containing Ba, Sr, Ca, Pr, Bi and Fe according to the stoichiometric ratio of the general chemical formula, and mix them evenly; (2) The powder mixed in step (1) is ball-milled with anhydrous ethanol and dried to obtain a dry mixed powder; (3) The dry mixed powder is pre-calcined; the pre-calcined product is naturally cooled and then finally calcined; after the final calcination is completed, it is cooled to room temperature in the furnace to obtain the iron-based perovskite air electrode material.

4. The preparation method according to claim 3, characterized in that, The pre-calcination temperature in step (3) is 700-900℃ and the time is 5-15 h; the final calcination temperature is 1000-1200℃ and the time is 3-10 h.

5. The preparation method according to claim 3, characterized in that, In step (1), the Ba source precursor is BaCO3; the Sr source precursor is SrCO3; the Ca source precursor is CaCO3; and the Pr source precursor is Pr6O. 11 Bi₂O₃ was selected as the Bi source precursor; Fe₂O₃ was selected as the Fe source precursor.

6. The preparation method according to claim 3, characterized in that, In step (2), the ball milling speed is 300-500 r / min and the time is 6-15 h; the drying temperature is 50-60 ℃.

7. The application of the iron-based perovskite air electrode material according to any one of claims 1-2, characterized in that, The material is used to prepare reversible solid oxide batteries.

8. The application according to claim 7, characterized in that, The specific application method is as follows: the iron-based perovskite air electrode material is mixed with an organic binder and ground into a uniform slurry; the slurry is coated on both sides of the electrolyte layer of the solid oxide battery, and after sintering, an air electrode layer for reversible solid oxide batteries is formed.

9. The application according to claim 8, characterized in that, The organic binder is a mixture of ethyl cellulose and terpineol in a mass ratio of 9:1; the mass ratio of the air electrode material to the organic binder is 1:

2.

10. The application according to claim 8, characterized in that, The sintering conditions are: calcination at 1000-1100 ℃ for 3-5 h in air atmosphere.

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