Device and method for manufacturing lattice oxygen vacancies in oxide under assistance of electric field

Abstract

The invention belongs to the technical field of oxide films / coatings, and particularly relates to a device and a method for manufacturing lattice oxygen vacancies in oxides under the assistance of an electric field. The device comprises a tubular furnace, a quartz tube penetrating through a heating cavity of the tubular furnace, a coating sample clamping unit arranged in the quartz tube, a power supply and a monitoring loop. Two ends of the quartz tube are sealed through vacuum sealing flanges. During use, a sample with an oxide coating is fixed in the clamping unit and placed in a constant-temperature area of a tubular furnace to be heated, meanwhile, current is applied through the wire, and oxygen in oxide lattices is promoted to escape under the synergistic effect of a thermal field and an electric field, so that high-concentration lattice oxygen vacancies are formed in the coating. The method has the advantages of simple process and controllable conditions, and can effectively regulate and control the physical and chemical properties of the oxide film / coating on the premise of not introducing foreign impurities and not destroying the integrity of the coating.

Description

Technical Field

[0001] This invention belongs to the field of oxide thin film / coating technology, specifically relating to an apparatus and method for creating lattice oxygen vacancies in oxides using an electric field-assisted process. Background Technology

[0002] Oxide films / coatings (such as ZrO2, TiO2, CeO2, and ZnO) are used in photoelectrocatalysis, gas sensors, solid oxide fuel cells, and resistive switching memory due to their chemical stability and dielectric properties. Lattice oxygen vacancies, as a key point defect in oxide materials, can modulate the band structure and increase carrier concentration, thereby effectively regulating the material's conductivity, optical absorption characteristics, and surface catalytic activity. Therefore, the fabrication and manipulation of lattice oxygen vacancies in oxide coatings is an important means to improve the performance of oxide coatings.

[0003] Currently, traditional methods for creating lattice oxygen vacancies in oxide manufacturing mainly include heterovalent element doping and high-energy particle bombardment. Heterovalent element doping generates oxygen vacancies by introducing low-valence metal cations to replace high-valence cations in the lattice. This method requires a significant increase in doping concentration to obtain high-concentration oxygen vacancies, which easily leads to component segregation, lattice distortion, or the precipitation of second-phase impurities. High-energy particle bombardment utilizes high-energy particles such as plasma, ion beams, or electron beams to bombard the surface of oxide films / coatings, physically stripping oxygen atoms from the lattice. However, high-energy particle bombardment easily damages the film / coating surface, leading to a significant increase in surface roughness, and even causing microcracks or peeling of the coating, compromising the structural integrity of the film / coating.

[0004] In summary, developing a device and method for efficiently and controllably creating lattice oxygen vacancies in oxide thin films / coatings without introducing foreign impurity atoms or compromising the structural integrity of the film / coating is a pressing technical problem in the field of oxide thin films / coatings. Summary of the Invention

[0005] To address the above technical problems, this invention provides an apparatus and method for generating lattice oxygen vacancies in oxides using an electric field. The coating sample is fixed in a quartz tube by a coating sample clamping unit, and the coating sample is heated to a preset temperature using a tube furnace. Then, the power supply is turned on, and a current is applied to both ends of the coating surface. Under the coupling effect of the electric field and the thermal field, lattice oxygen in the oxide escapes, thereby generating lattice oxygen vacancies inside the thin film / coating.

[0006] An apparatus for creating lattice oxygen vacancies in oxides using an electric field-assisted method, comprising:

[0007] Tubular furnace;

[0008] A quartz tube extends axially through the heating chamber of the tubular furnace, and both ends of the quartz tube are sealed by vacuum-sealed flanges.

[0009] A coating sample clamping unit is located inside the quartz tube and within the constant temperature zone of the tube furnace, and is used to clamp and fix the coating sample.

[0010] Power supply, used to provide an external electric field;

[0011] A wire passes through the opening on the vacuum-sealed flange and enters the quartz tube, and is connected in series with the coating sample clamping unit and the power supply to form a current loop.

[0012] A multimeter is connected in series in the current loop to monitor the loop current in real time.

[0013] Furthermore, the coating sample clamping unit includes:

[0014] A pair of insulating pads;

[0015] A pair of metal clamps are located on both sides of the coating sample to clamp and fix the insulating pad, the coating sample and the electrode sheet.

[0016] The electrode sheet is positioned between the coated sample and the metal clamp, and is in electrical contact with the conductive paste applied to the surface of the coated sample.

[0017] Furthermore, a gasket is provided between the vacuum sealing flange and the quartz tube; the vacuum sealing flange is provided with an opening for the wire to pass through.

[0018] A method for creating lattice oxygen vacancies using the aforementioned apparatus includes the following steps:

[0019] Step S1: Prepare coating sample: Prepare oxide coating on substrate surface using coating or deposition process to obtain coating sample. The coating process includes sol-gel method, spraying method, spin coating method, dip-coating method, and deposition process includes chemical vapor deposition, physical vapor deposition, and atomic layer deposition.

[0020] Step S2: Assemble the sample unit: Apply conductive paste to both ends of the coated sample and clamp and fix the insulating pad, the coated sample and the electrode sheet with metal clamps to form a coated sample clamping unit.

[0021] Step S3: Connect the current loop: Place the coating sample clamping unit inside the quartz tube, and use wires to connect the metal clamp in series with the power supply and multimeter outside the tube to form a current loop;

[0022] Step S4, Heating treatment: Place the quartz tube in a tube furnace, set the temperature of the tube furnace to 300~1200°C, and heat to the set temperature at a heating rate of 5~50°C / min;

[0023] Step S5, heat preservation and electric field assisted treatment: heat preservation at the set temperature for 3~12h, while starting the power supply and applying a current of 0.5A-50A to the coating sample. Through the coupling effect of electric field and thermal field, lattice oxygen in oxide is released to form lattice oxygen vacancies.

[0024] Step S6, Cooling: After the treatment is completed, turn off the power and the tube furnace in sequence, and let the coated sample cool to room temperature with the furnace at a rate of 5~30°C / min.

[0025] Furthermore, the oxide coating prepared in step S1 includes various metal oxides or composite oxides such as ZrO2, TiO2, CeO2, ZnO, Cr2O3 or Al2O3.

[0026] Furthermore, in step S4, the temperature of the tube furnace is 300~1200°C, and the heating rate is 5~50°C / min.

[0027] Furthermore, in step S5, the heat preservation time is 3~12h, and the applied current is 0.5A-50A.

[0028] Furthermore, in step S6, the cooling rate is 5~30°C / min. The beneficial effects of this invention are:

[0029] 1. The electric field-assisted method for creating lattice oxygen vacancies in oxides used in this invention avoids the damage to the thin film / coating structure caused by heterovalent element doping or high-energy particle impact, thus ensuring the integrity and compactness of the macroscopic structure of the oxide thin film / coating.

[0030] 2. The present invention provides an apparatus and method for producing lattice oxygen vacancies in oxides using an electric field-assisted process. The process is simple, easy to operate, and applicable to the production and control of lattice oxygen vacancies in different oxide systems, and has good versatility. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall structure of an apparatus for creating lattice oxygen vacancies in oxides using an electric field assisted, provided by an embodiment of the present invention.

[0032] Figure 2 This is a partially enlarged structural schematic diagram of the coating sample clamping unit in an embodiment of the present invention.

[0033] Figure 3The images show a comparison of the surface scanning electron microscope (SEM) morphology and electron paramagnetic resonance (EPR) oxygen vacancy spectrum of the ZrO2 coatings in Embodiment 2 of the present invention, with and without electric field assistance.

[0034] Figure 4 The images show a comparison of the surface scanning electron microscope (SEM) morphology of the Cr2O3 coatings without and with electric field assistance in Embodiment 3 of the present invention, as well as a comparison of the electron paramagnetic resonance (EPR) oxygen vacancy spectrum.

[0035] Figure 5 The images show a comparison of the surface scanning electron microscope (SEM) morphology of the TiO2 coatings in Embodiment 4 of the present invention with and without electric field assistance, as well as a comparison of oxygen vacancies using electron paramagnetic resonance (EPR).

[0036] Figure 6 The images show a comparison of the surface scanning electron microscope (SEM) morphology of the Al2O3 coatings in Embodiment 5 of the present invention, with and without electric field assistance, as well as a comparison of the electron paramagnetic resonance (EPR) oxygen vacancy spectra.

[0037] In the figure: 1-Tube furnace; 2-Quartz tube; 3-Vacuum sealing flange; 4-Gasket; 5-Multimeter; 6-Power supply; 7-Wire; 8-Insulating gasket; 9-Metal clamp; 10-Coating sample; 11-Electrode sheet. Detailed Implementation

[0038] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0039] Example 1

[0040] like Figure 1 As shown, this embodiment provides an apparatus for creating lattice oxygen vacancies in oxides using an electric field-assisted process. The apparatus includes a tube furnace 1, a quartz tube 2, a vacuum-sealed flange 3, a rubber gasket 4, a multimeter 5, a power supply 6, wires 7, and a coating sample clamping unit located inside the cavity. Both ends of the quartz tube 2 are sealed by the vacuum-sealed flange 3 and the gasket 4.

[0041] like Figure 2The diagram shown is a partially enlarged schematic of the coating sample clamping unit. This unit consists of an insulating pad 8, metal clamps 9, and electrode plates 11. Conductive paste is applied to both ends of the surface of the coating sample 10. The coating sample 10 is placed on the insulating pad 8, and the electrode plates 11 and the coating sample are clamped using two metal clamps 9. A wire 7 is connected to the metal clamps 9 and to a power supply 6 and a multimeter 5 to form a current loop.

[0042] The specific implementation steps of this embodiment are as follows:

[0043] Step S1: Prepare an oxide coating on the substrate surface using one of the following coating processes: sol-gel, spraying, chemical vapor deposition, physical vapor deposition, etc., to obtain a thin film / coating sample;

[0044] Step S2: Apply conductive paste to both ends of the surface of the coating sample, and assemble and clamp the coating sample, electrode sheet and insulating pad using metal clamps;

[0045] Step S3: Connect the metal clamp, power supply, and multimeter in series using wires to form a current loop;

[0046] Step S4: Set the temperature of the tube furnace to 300~1200°C, specifically 900°C, and the heating rate to 5~50°C / min, specifically 20°C / min;

[0047] Step S5: Keep the sample to be coated at the set temperature for 3~12h, specifically 10h, and at the same time turn on the power supply and apply a current of 0.5A-50A, specifically 20A;

[0048] Step S6: After the treatment is completed, turn off the power and the tube furnace in sequence, and let the coated sample cool to room temperature with the furnace at a rate of 5~30°C / min, specifically 20°C / min.

[0049] Example 2

[0050] A method for creating lattice oxygen vacancies in oxides using an electric field-assisted process includes:

[0051] (1) Zirconium sol is prepared by dissolving metallic zirconium salt in an alcohol solvent and adding a complexing agent using the sol-gel method; the zirconium sol is coated onto the surface of a metal substrate by spin coating and then preheated to obtain a ZrO2 coating.

[0052] (2) Apply conductive paste to both sides of the upper surface of the ZrO2 coating, arrange electrode sheets in contact with the conductive paste, and assemble and clamp the coating sample, electrode sheets and insulating pads using metal clamps.

[0053] (3) Connect the metal clamp, power supply and multimeter in series with wires to form a current loop.

[0054] (4) Place the coating sample in a tube furnace and heat it to 900°C at a rate of 20°C / min, and hold for 4 hours;

[0055] (5) Apply current to the coating through a wire using a power source. Set the current intensity to 20A and keep it powered on for 5 hours.

[0056] (6) After the treatment is completed, turn off the power and control the sample to cool to room temperature at a rate of 20°C / min with the furnace to obtain a ZrO2 coating rich in lattice oxygen vacancies (ZrO2-electric field assisted).

[0057] To verify the effect of electric field assistance, a blank control sample (ZrO2-without electric field assistance) was also prepared in Example 2. The preparation process of this control sample was the same as the above steps, except that no electric field assistance was applied. The surface scanning electron microscope (SEM) morphology and electron paramagnetic resonance (EPR) oxygen vacancy spectrum of the electric field-assisted sample and the blank control sample in this example are shown below. Figure 3 As shown.

[0058] Example 3

[0059] A method for creating lattice oxygen vacancies in oxides using an electric field-assisted process includes:

[0060] (1) Zirconium sol is prepared by dissolving metallic chromium salt in an alcohol solvent and adding a complexing agent using the sol-gel method; the zirconium sol is coated onto the surface of a metal substrate by spin coating and a Cr2O3 coating is obtained after preheating treatment.

[0061] (2) Apply conductive paste to both sides of the upper surface of the Cr2O3 coating, arrange electrode sheets in contact with the conductive paste, and assemble and clamp the coating sample, electrode sheets and insulating pads with metal clamps.

[0062] (3) Connect the metal clamp, power supply and multimeter in series with wires to form a current loop.

[0063] (4) Place the coating sample in a tube furnace and heat it to 900°C at a rate of 20°C / min, and hold for 4 hours;

[0064] (5) Apply current to the coating through a wire using a power source. Set the current intensity to 20A and keep it powered on for 5 hours.

[0065] (6) After the treatment is completed, turn off the power and control the sample to cool to room temperature at a rate of 20°C / min with the furnace to obtain a Cr2O3 coating rich in lattice oxygen vacancies (Cr2O3-electric field assisted).

[0066] To verify the effect of electric field assistance, a blank control sample (Cr2O3-without electric field assistance) was also prepared in Example 3. The preparation process of this control sample was the same as the above steps, except that no electric field assistance was applied. The surface scanning electron microscope (SEM) morphology and electron paramagnetic resonance (EPR) oxygen vacancy spectrum of the electric field-assisted sample and the blank control sample in this example are shown below. Figure 4 As shown.

[0067] Example 4

[0068] A method for creating lattice oxygen vacancies in oxides using an electric field-assisted process includes:

[0069] (1) Zirconium sol is prepared by dissolving metallic titanium salt in an alcohol solvent and adding a complexing agent using the sol-gel method; the zirconium sol is coated onto the surface of a metal substrate by spin coating and then preheated to obtain a TiO2 coating.

[0070] (2) Apply conductive paste to both sides of the upper surface of the TiO2 coating, arrange electrode sheets in contact with the conductive paste, and assemble and clamp the coating sample, electrode sheets and insulating pads with metal clamps.

[0071] (3) Connect the metal clamp, power supply and multimeter in series with wires to form a current loop.

[0072] (4) Place the coating sample in a tube furnace and heat it to 900°C at a rate of 20°C / min, and hold for 4 hours;

[0073] (5) Apply current to the coating through a wire using a power source. Set the current intensity to 20A and keep it powered on for 5 hours.

[0074] (6) After the treatment is completed, turn off the power and control the sample to cool to room temperature at a rate of 20°C / min with the furnace to obtain a TiO2 coating rich in lattice oxygen vacancies (TiO2-electric field assisted).

[0075] To verify the effect of electric field assistance, a blank control sample (TiO2 without electric field assistance) was also prepared in Example 4. The preparation process of this control sample was the same as the above steps, except that no electric field assistance was applied. The surface scanning electron microscope (SEM) morphology and electron paramagnetic resonance (EPR) oxygen vacancy spectrum of the electric field-assisted sample and the blank control sample in this example are shown below. Figure 5 As shown.

[0076] Example 5

[0077] A method for creating lattice oxygen vacancies in oxides using an electric field-assisted process includes:

[0078] (1) Using the sol-gel method, aluminum salt is dissolved in an alcohol solvent and a complexing agent is added to prepare aluminum sol; the aluminum sol is coated onto the surface of a metal substrate by spin coating and Al2O3 coating is obtained after preheating treatment.

[0079] (2) Apply conductive paste to both sides of the upper surface of the Al2O3 coating, arrange electrode sheets in contact with the conductive paste, and assemble and clamp the coating sample, electrode sheets and insulating pads with metal clamps.

[0080] (3) Connect the metal clamp, power supply and multimeter in series with wires to form a current loop.

[0081] (4) Place the coating sample in a tube furnace and heat it to 900°C at a rate of 20°C / min, and hold for 4 hours;

[0082] (5) Apply current to the coating through a wire using a power source. Set the current intensity to 20A and keep it powered on for 5 hours.

[0083] (6) After the treatment is completed, turn off the power and control the sample to cool to room temperature at a rate of 20°C / min with the furnace to obtain an Al2O3 coating rich in lattice oxygen vacancies (Al2O3-electric field assisted).

[0084] To verify the effect of electric field assistance, a blank control sample (Al2O3 without electric field assistance) was also prepared in Example 5. The preparation process of this control sample was the same as the above steps, except that no electric field assistance was applied. The surface scanning electron microscope (SEM) morphology and electron paramagnetic resonance (EPR) oxygen vacancy spectrum of the electric field-assisted sample and the blank control sample in this example are shown below. Figure 6 As shown.

[0085] refer to Figure 3 Comparison of the scanning electron microscope (SEM) morphology of the ZrO2 coating surface before and after electric field treatment reveals that both surfaces exhibit a dense and uniform microstructure. No obvious cracks or pores were observed in the electric field-assisted treatment coating, indicating that the treatment maintained the good structural integrity of the coating. Combined with electron paramagnetic resonance (EPR) oxygen vacancy spectrum analysis, the electric field-treated sample showed a significantly enhanced lattice oxygen vacancy signal, confirming that electric field assistance can effectively induce a high concentration of lattice oxygen vacancies in the ZrO2 coating.

[0086] refer to Figure 4For the Cr2O3 coating, surface scanning electron microscopy (SEM) results showed that the coating surface was continuous and smooth before and after electric field-assisted treatment, without defects such as microcracks or pores, indicating that the coating has excellent surface quality. Further analysis of the electron paramagnetic resonance (EPR) oxygen vacancy spectrum revealed that the peak intensity of lattice oxygen vacancies in the coating was significantly increased after electric field treatment compared to the original sample, indicating that electric field assistance significantly increased the lattice oxygen vacancy concentration inside the Cr2O3 coating.

[0087] refer to Figure 5 Combined with surface scanning electron microscopy (SEM) morphology analysis, the TiO2 coating maintained a uniform and dense microstructure and structural integrity before and after electric field treatment. Comparison of electron paramagnetic resonance (EPR) oxygen vacancy spectra showed that the intensity of the characteristic peak of lattice oxygen vacancies in the electric field-treated sample was significantly higher than that in the untreated sample. This strongly demonstrates that electric field assistance can promote the escape of lattice oxygen, thereby introducing abundant lattice oxygen vacancies into the TiO2 coating.

[0088] refer to Figure 6 For the Al2O3 coating, surface scanning electron microscopy (SEM) morphology comparison showed that the electric field-assisted treatment coating maintained the same density as the untreated sample, and no macroscopic defects such as pinholes or cracks were observed. In the electron paramagnetic resonance (EPR) oxygen vacancy spectrum, the electric field-treated coating showed a stronger lattice oxygen vacancy signal peak, further verifying the effectiveness of electric field-assisted technology in promoting the formation of lattice oxygen vacancies in Al2O3 coating.

[0089] In summary, through experimental verification on four typical oxide coatings—ZrO2, Cr2O3, TiO2, and Al2O3—the apparatus and method for creating lattice oxygen vacancies in oxides using an electric field-assisted process, as described in this invention, demonstrate consistent effectiveness. Experimental results confirm that this method can achieve controllable creation of lattice oxygen vacancies in oxides while maintaining the integrity of the coating's macroscopic morphology and its dense structure. This fully demonstrates that the apparatus and method provided by this invention have significant universality for oxide systems of different types and can be widely applied in the field of oxide thin film / coating modification technology.

[0090] This invention has the following features and effects:

[0091] 1. Maintaining the integrity of the coating structure and avoiding the defects of traditional methods: This invention employs an electric field-assisted heat treatment method, where an electric current is directly applied to the coating sample, driving the directional migration and escape of lattice oxygen based on thermal activation. This process does not rely on heterovalent element doping, avoiding component segregation, lattice distortion, or second-phase precipitation caused by excessive doping; it is also different from high-energy particle bombardment, and will not cause physical damage to the coating surface, thus effectively maintaining the density, smoothness, and structural integrity of the coating.

[0092] 2. The process is simple and controllable, with good versatility and scalability: The device has a simple structure, integrating tube furnace heating and an external electric field into a sealed quartz tube environment, making the process easy to operate and repeat. By adjusting parameters such as temperature, holding time, and current, the concentration and distribution of oxygen vacancies can be precisely controlled. Examples show that this method is applicable to various oxide systems such as ZrO2, TiO2, Cr2O3, and Al2O3, demonstrating good material versatility and process adaptability, facilitating its application in the performance modification of various oxide functional coatings.

[0093] 3. Achieving pure, efficient, and controllable oxygen vacancy generation: This invention utilizes the coupling effect of electric and thermal fields to directly act on the oxide lattice, promoting the migration and escape of intrinsic oxygen ions to form high-purity lattice oxygen vacancies, thus avoiding the introduction of foreign impurities. This method boasts high oxygen vacancy generation efficiency, and the process can be controlled through electrical parameters, providing an effective, clean, and controllable defect engineering approach for optimizing the conductivity, optical properties, and catalytic activity of oxide coatings.

[0094] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed herein should be included within the scope of protection of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An apparatus for creating lattice oxygen vacancies in oxides using an electric field-assisted process, characterized in that, include: Tubular furnace (1); A quartz tube (2) extends axially through the heating chamber of the tubular furnace (1), and both ends of the quartz tube (2) are sealed by vacuum sealing flanges (3). The coating sample clamping unit is located inside the quartz tube (2) and within the constant temperature zone of the tube furnace (1) for clamping and fixing the coating sample (10). Power supply (6) is used to provide an external electric field; The wire (7) passes through the opening on the vacuum sealing flange (3) and enters the quartz tube (2), and is connected in series with the coating sample clamping unit and the power supply (6) to form a current loop; A multimeter (5) is connected in series in the current loop to monitor the loop current in real time.

2. The apparatus according to claim 1, characterized in that, The coating sample clamping unit includes: A pair of insulating pads (8); A pair of metal clamps (9) are located on both sides of the coating sample (10) to clamp and fix the insulating pad (8), the coating sample (10) and the electrode sheet (11). Electrode sheet (11) is disposed between the coating sample (10) and the metal clamp (9) and is in electrical contact with the conductive paste coated on the surface of the coating sample (10).

3. The apparatus according to claim 1, characterized in that, A gasket (4) is provided between the vacuum sealing flange (3) and the quartz tube (2); the vacuum sealing flange (3) is provided with an opening through which a wire can pass.

4. A method for generating lattice oxygen vacancies using the apparatus according to any one of claims 1-3, characterized in that, Includes the following steps: Step S1: Prepare coating sample: Prepare oxide coating on substrate surface using coating process or deposition process to obtain coating sample (10). The coating process includes sol-gel method, spraying method, spin coating method, dip-coating method, and deposition process includes chemical vapor deposition method, physical vapor deposition method, and atomic layer deposition method. Step S2: Assemble the sample unit: Apply conductive paste to both ends of the coated sample (10), and clamp and fix the insulating pad (8), the coated sample (10) and the electrode sheet (11) with metal clamps (9) to form a coated sample clamping unit. Step S3: Connect the current loop: Place the coating sample clamping unit inside the quartz tube (2), and use the wire (7) to connect the metal clamp (9) in series with the power supply (6) and the multimeter (5) outside the tube to form a current loop; Step S4, Heating treatment: Place the quartz tube (2) in a tube furnace (1), set the temperature of the tube furnace to 300~1200°C, and heat it to the set temperature at a heating rate of 5~50°C / min; Step S5, heat preservation and electric field assisted treatment: heat preservation at the set temperature for 3~12h, and at the same time start the power supply (6) to apply a current of 0.5A-50A to the coating sample (10). Through the coupling effect of electric field and thermal field, the lattice oxygen in the oxide escapes and forms lattice oxygen vacancies. Step S6, Cooling: After the treatment is completed, turn off the power supply (6) and the tube furnace (1) in sequence, so that the coating sample (10) is cooled to room temperature at a rate of 5~30°C / min along with the furnace.

5. The method according to claim 4, characterized in that, The oxide coating prepared in step S1 is a variety of metal oxides or composite oxides, such as ZrO2, TiO2, CeO2, ZnO, Cr2O3 or Al2O3.

6. The method according to claim 4, characterized in that, In step S4, the temperature of the tubular furnace is 300~1200°C, and the heating rate is 5~50°C / min.

7. The method according to claim 4, characterized in that, In step S5, the heat preservation time is 3~12h, and the applied current is 0.5A-50A.

8. The method according to claim 4, characterized in that, The cooling rate in step S6 is 5~30°C / min.

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