A method for producing a conductive oxide ceramic

Abstract

This invention discloses a method for preparing conductive oxide ceramics, specifically comprising: mixing oxide matrix raw materials and dopant raw materials according to a predetermined formula; obtaining a doped oxide mixed powder after drying, calcination, and grinding; pressing the doped oxide mixed powder into a first green body; subjecting the first green body to a first rapid sintering to promote the solid solution of dopant elements in the oxide matrix, inhibit the volatilization of matrix elements and dopant elements under long-term heat preservation conditions, and introduce intrinsic conductive defects and impurity conductive defects to obtain a first sintered body; crushing and grinding the first sintered body to obtain a conductive powder for secondary sintering; pressing the powder for secondary sintering into a second green body; subjecting the second green body to a second sintering to densify the second green body to obtain conductive oxide ceramics. This invention promotes the solid solution of dopant elements, overcomes thermodynamic and kinetic limitations, improves the degree of densification, and regulates grain boundary electrical transport, and is applicable to various conductive oxide ceramic systems.

Description

Technical Field

[0001] This invention belongs to the field of conductive ceramics and powder metallurgy technology, and particularly relates to a method for preparing conductive oxide ceramics. Background Technology

[0002] Conductive oxide ceramics combine the high-temperature resistance, corrosion resistance, chemical stability, and tunable electrical transport properties of oxide ceramics, making them valuable for applications in transparent conductive targets, thermoelectric materials, high-temperature resistive materials, temperature coefficient resistive materials, uncooled infrared detectors, magnetoresistive sensors, solid oxide fuel cell electrodes, optoelectronic devices, and antistatic components. Typical systems include ZnO, SnO2, In2O3, TiO2, Ga2O3, SrTiO3, CaMnO3, as well as perovskite-type manganate, cobaltate, and nickelate.

[0003] Existing conductive oxide ceramics are typically prepared using traditional solid-state reactions, prolonged high-temperature pressureless sintering, hot-pressing sintering, spark plasma sintering, or reducing atmosphere sintering. While these methods can promote densification or introduce conductive defects to some extent, they still have the following drawbacks: First, the solid solution of some dopants in the oxide matrix is ​​limited by thermodynamic stability and diffusion kinetics, easily leading to the formation of coarse second phases or dopant segregation. Second, prolonged high-temperature holding can easily cause the loss of volatile components such as Zn, Ga, In, Sn, Sb, Bi, Ag, and K, thereby altering the nominal composition. Third, a rapid densification process alone may not be conducive to the complete solid solution of dopants. Fourth, even after the initial high-temperature treatment alone, the porosity and grain boundary barriers of the sample may still be too high, resulting in insufficient carrier mobility and conductivity.

[0004] Reference patent CN119430921A discloses an oxygen-deficient oxide ceramic material and its preparation method. The main idea is to press oxide ceramic powder into a green body and preheat it, then apply direct current to trigger flash sintering to achieve rapid deoxidation. Subsequently, the deoxidized ceramic is pulverized and sieved, and then sintered again under low oxygen partial pressure to obtain the oxygen-deficient oxide ceramic. The core of this technology lies in utilizing the electrochemical reduction effect of the flash sintering process to rapidly create an oxygen-deficient state, and maintaining the oxygen stoichiometry through secondary sintering under low oxygen partial pressure. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing conductive oxide ceramics, so as to solve the problems of insufficient doping and solid solution, loss of volatile components, insufficient densification, high grain boundary barrier, long preparation cycle and difficulty in stable control of electrical transport properties in existing methods.

[0006] The present invention provides a method for preparing a conductive oxide ceramic, comprising the following steps:

[0007] Step 1: Mix the oxide matrix raw material and the dopant raw material according to the set stoichiometric ratio, and obtain the doped oxide mixed powder after drying, calcination and grinding.

[0008] Step 2: Press the doped oxide mixed powder into a first green compact, and perform a first rapid sintering on the first green compact to make the peak temperature of the first green compact reach 1000-2500℃ and hold it for 5-120 s, so as to promote the solid solution of the doped element in the oxide matrix, suppress the volatilization of matrix elements and doped elements under long-term holding conditions, and introduce intrinsic conductive defects and impurity conductive defects to obtain the first sintered body.

[0009] Step 3: Crush and grind the first sintered body to obtain conductive powder for secondary sintering.

[0010] Step 4: Press the secondary sintering powder into a second green body, and perform a second sintering on the second green body to densify it, thereby obtaining a conductive oxide ceramic.

[0011] The second step of sintering is selected from one of spark plasma sintering, hot pressing sintering, and flash sintering.

[0012] Furthermore, the oxide matrix material is a dopant-compatible conductive oxide ceramic matrix, including ZnO, SnO2, In2O3, TiO2, Ga2O3, SrTiO3, CaMnO3, and La. 1-x A x MnO3, La 1-x A x CoO3, LaNiO3, LaCo 1-x Ni x One or more of O3, wherein A is one or more of Ca, Sr, Ag, K, and Na, 0 <x<0.5。

[0013] Furthermore, the dopant material is used to form one or more conductive defects in the oxide matrix, including donor defects, acceptor defects, oxygen vacancies, metal interstices, valence transition defects, A-site substitution defects, and B-site substitution defects.

[0014] Furthermore, in step 1, the calcination temperature is 300-900℃ and the calcination time is 1-10 h.

[0015] Furthermore, the first rapid sintering is selected from one of ultrafast high-temperature sintering, flash sintering, and high-temperature plasma treatment.

[0016] Furthermore, the high-temperature plasma treatment employs electric arc plasma, atmospheric plasma, nitrogen plasma, argon plasma, or a combination thereof to directly heat the first green billet.

[0017] Furthermore, in step 4, the sintering pressure in the second sintering step is 10-200 MPa, the sintering time is 1 min-3 h, and the sintering temperature is 500-2200℃.

[0018] Furthermore, in step 2, the atmosphere for the first rapid sintering is a protective atmosphere containing air, oxygen, nitrogen, argon, vacuum, or hydrogen, carbon monoxide, or methane, with a volume fraction of reducing gas not less than 0.1%.

[0019] The atmosphere for sintering in the second step of step 4 is a protective atmosphere containing air, oxygen, nitrogen, argon, vacuum, or containing hydrogen, carbon monoxide, or methane, with a volume fraction of reducing gas not less than 0.1%.

[0020] The beneficial technical effects of this invention compared to the prior art are as follows:

[0021] (1) The first rapid sintering adopts high temperature and short time treatment, which can promote the solid solution of doped elements and break through the thermodynamic and kinetic limitations of doped solid solution.

[0022] (2) Short-time high-temperature treatment reduces the loss of volatile components during long-term sintering, but introduces a large number of non-equilibrium conductive defects.

[0023] (3) The first sintered body is crushed to form a conductive secondary powder, which is beneficial to the rapid densification of subsequent discharge plasma sintering, hot pressing sintering or flash sintering.

[0024] (4) The second step of sintering can further improve the integrity of the ceramic body and reduce the grain boundary barrier, improve the electrical transport performance of conductive oxide ceramics, and reflect the functional division of the first step of solid solution and defect control and the second step of densification and grain boundary control.

[0025] (5) This method is applicable to a variety of conductive oxide ceramic systems, and is not limited to ZnO. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of the conductive oxide ceramic preparation method of the present invention. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] The present invention provides a method for preparing conductive oxide ceramics, the process flow of which is as follows: Figure 1As shown, the process includes: mixing, drying, calcining and grinding oxide matrix raw materials and dopant raw materials; pressing the mixed powder into a first green body and performing a high-temperature short-time first rapid sintering; crushing and grinding the first sintered body to obtain a conductive powder for secondary sintering; pressing the powder into a second green body and performing a second sintering step by spark plasma sintering, hot pressing sintering or flash sintering to obtain a conductive oxide ceramic.

[0029] The objective of this invention is not simply to prepare oxygen-deficient oxide ceramics, but rather to develop dopant-compatible conductive oxide ceramics. The first step, high-temperature short-time sintering, promotes solid solution of dopant elements, overcomes thermodynamic and kinetic limitations, avoids component volatilization caused by prolonged holding, and introduces intrinsic and impurity conductive defects. Subsequently, the first sintered body is pulverized and subjected to a second sintering step to further improve densification and regulate grain boundary electrical transport. The core innovation of this invention lies in the preparation method itself, without involving innovation in the sintering apparatus structure; the power supply, mold, heating unit, plasma generation unit, and pressure loading unit used are all conventional equipment in the field. Therefore, this invention differs from the reference patent in terms of the technical problem to be solved, the main mechanism of action, and the resulting technical effects.

[0030] From the perspective of material selection, wide-bandgap or semiconductor oxides such as ZnO, SnO2, In2O3, TiO2, Ga2O3, and SrTiO3 can increase electron concentration through high-valence cation substitution, anion vacancies, or shallow donor defects; CaMnO3 can be doped with La, Y, Nb, Ta, etc., to form n-type conductive ceramics; La 1-x A x MnO3-type perovskite manganate can have its Mn content modulated by doping with Ca, Sr, Ag, K, etc. at the A-site. 3+ / Mn 4+ Proportional, double exchange action, metal-insulator transition temperature, temperature coefficient resistance and magnetoresistance; La 1-x A x CoO3, LaNiO3 and LaCo 1-x Ni x O3 exhibits high electronic conductivity and can be used as an electrode, interconnect, or high-temperature conductive oxide material. Based on the principle of matching effective ionic radius and crystal structure, when the dopant ion is compatible with the radius of the matrix cation and its valence state can generate donor, acceptor, or variable valence defects, doping solid solution and electrotransport modulation are more easily achieved.

[0031] In this invention, the necessity of the first rapid sintering lies in the following: First, short-time treatment within a high-temperature range of 1000-2500℃ can significantly improve the diffusion rate and solid solution reaction rate of dopant elements, thereby promoting the entry of dopant elements into the matrix lattice; the peak temperature refers to the temperature reached by the first green body, not the temperature of the plasma or heat source itself, and the specific peak temperature is determined based on the melting point, phase stability range, and volatility characteristics of the oxide matrix; Second, short-time holding of 5-120 s can reduce the volatilization loss of matrix components and dopant elements at high temperatures; Third, the rapid non-equilibrium thermal process can introduce intrinsic and impurity conductivity defects such as oxygen vacancies, intermetallic interstices, valence state changes, antisite defects, and dopant donor or acceptor defects into the oxide ceramic. The first rapid sintering can employ ultrafast high-temperature sintering, flash sintering, or high-temperature plasma treatment; wherein high-temperature plasma treatment includes direct heating of the green body by arc plasma, atmospheric plasma, nitrogen plasma, and argon plasma.

[0032] In this invention, the second sintering step is used for further densification and control of grain boundary states. For powders that have already undergone the first high-temperature short-time treatment, their conductivity and defect states have been improved. The second sintering step can achieve particle rearrangement, grain boundary bonding, porosity elimination, and reduction of grain boundary barriers in a relatively short time. The sintering temperature of the second step is limited to a total range of 500-2200℃, and the specific temperature can be selected by those skilled in the art based on the sintering activity, phase stability range, volatility characteristics, and target defect states of the oxide matrix. When S2 or S4 uses a protective atmosphere and contains a reducing gas, the reducing gas can be hydrogen, carbon monoxide, or methane, and the volume fraction of the reducing gas is not less than 0.1%, while the remaining gas can be nitrogen, argon, or other inert gases.

[0033] The embodiments of this invention are used to explain the invention, and not to limit the scope of protection of the invention. Unless otherwise stated, the relative density of the samples was determined by the Archimedes displacement method, and the room temperature conductivity was determined by the four-probe method.

[0034] Example 1

[0035] The material system in this embodiment is Ga-doped ZnO, with the doping composition being Zn. 1-x Ga x O 1+x / 2 Where x = 0.04. ZnO powder and Ga2O3 powder were weighed according to this nominal stoichiometric ratio, placed in a ball mill jar, and anhydrous ethanol was added as the medium. The mixture was then mixed using zirconia grinding balls. The resulting slurry was dried, calcined at 500℃ for 6 h to remove organic contaminants, and then ground again to obtain the initial mixed powder of Ga2O3 and ZnO.

[0036] The mixed powder was pressed into a first green compact, and then subjected to ultrafast high-temperature sintering. The peak temperature of the first green compact was 1600℃, and the holding time was 40 s. No external pressure was applied during the sintering process. This high-temperature short-time sintering promotes the solid solution of Ga in the ZnO grains, inhibits the volatilization of Zn and Ga-related components caused by long-term sintering, and introduces oxygen vacancies, zinc interstitials, and Ga... Zn Donor defect.

[0037] The first sintered body was crushed and ground into powder to obtain powder for secondary sintering. The powder was pressed into a second green body, and a second-step pressure-assisted flash sintering was performed under a pulsed current at a pressure of 50 MPa, raising the apparent temperature of the sample to 900-1200℃ and holding it for 2 min. After sintering, Ga-doped ZnO conductive ceramic was obtained.

[0038] The sample's relative density was 96.7%, and its room temperature conductivity was 649 S / cm. As a reference for the same process, when only the first rapid sintering was performed under the same powder ratio and calcination conditions, without the second sintering step after pulverization, the resulting UHS-Ga sample had a relative density of 90.1% and a room temperature conductivity of 223 S / cm. This demonstrates that the second sintering step can further improve density and reduce grain boundary barriers while retaining the effects of the first high-temperature short-time solid solution and defect introduction, resulting in a significant increase in conductivity. Compared to the UHS-Ga sample that only underwent the first rapid sintering step, the room temperature conductivity increased by approximately 191%.

[0039] Example 2

[0040] The material system in this embodiment is Al-doped ZnO, with a doping composition of Zn. 1-x Al x O 1+x / 2 Where x = 0.02. Weigh ZnO and A according to this nominal stoichiometric ratio. l2 O3 powder was mixed, dried, calcined at 500℃ for 4 h, and then ground. The powder was pressed into a first green body and subjected to a first rapid sintering using ultrafast high-temperature sintering, with a peak temperature of 1550℃ and a holding time of 35 s. No external pressure was applied during the sintering process.

[0041] The first sintered body was crushed and ground, then pressed into a second green body. A second-step pressure-assisted flash sintering was performed at 60 MPa, with an apparent temperature of 900-1200℃ and a sintering time of 2 min, yielding Al-doped ZnO conductive ceramics. The sample had a relative density of 97.2% and a room temperature conductivity of 820 S / cm. Performance analysis showed that Al… 3+ Alternative to Zn 2+ It can serve as a donor source and increase carrier concentration. High-temperature, short-time rapid sintering is beneficial for Al solid solution and avoids Zn volatilization.

[0042] Example 3

[0043] The material system in this embodiment is In-doped ZnO, with a doping composition of Zn. 1-x In x O 1+x / 2 Where x=0.02. ZnO and In2O3 powders were weighed according to the nominal stoichiometric ratio, mixed, and calcined at 550℃ for 4 h. The powder was pressed into a first green body and subjected to a first rapid sintering using ultrafast high-temperature sintering, with a peak temperature of 1600℃ and a holding time of 45 s. No external pressure was applied during the sintering process.

[0044] The first sintered body was crushed and ground, and the resulting secondary powder was pressed into a second green body. A second-step pressure-assisted flash sintering was then performed at 50 MPa. The apparent temperature of the sample was 900-1200℃, and the sintering time was 2 min, yielding In-doped ZnO conductive ceramics. The sample had a relative density of 96.4% and a room temperature conductivity of 710 S / cm. Performance analysis showed that In... 3+ With Zn 2+ The ionic radii are compatible, which is beneficial for solid solution; high-temperature short-time treatment improves the diffusion of In element, and the second-step sintering improves the electrotransport of grain boundaries.

[0045] Example 4

[0046] The material system in this embodiment is Al and Ga co-doped ZnO, with a doping composition of Zn. 1-x-y Al x Ga y O 1+(x+y) / 2 Where x = 0.015 and y = 0.015. Weigh ZnO and A according to this nominal stoichiometric ratio. l2 O3 and Ga2O3 powders were mixed and calcined at 500℃ for 4 h. The powder was pressed into a first green body and subjected to a first rapid sintering using ultrafast high-temperature sintering, with a peak temperature of 1600℃ and a holding time of 40 s. No external pressure was applied during the sintering process.

[0047] The first sintered body was crushed, ground, and pressed into a second green body. A second-step pressure-assisted flash sintering was then performed at 60 MPa, with an apparent temperature of 900-1200℃ and a sintering time of 2 min, yielding Al-Ga co-doped ZnO conductive ceramics. The sample had a relative density of 97.0% and a room temperature conductivity of 960 S / cm. Performance analysis showed that Al doping is beneficial for increasing carrier concentration, while Ga doping is beneficial for forming stable donor defects; the combination of both improves conductivity and thermal stability.

[0048] Example 5

[0049] The material system in this embodiment is Al and In co-doped ZnO, with a doping composition of Zn. 1-x-y Al x In y O 1+(x+y) / 2 Where x=0.015 and y=0.005. ZnO, Al2O3, and In2O3 powders were weighed according to the nominal stoichiometric ratio, mixed, and calcined at 500℃ for 4 hours. The powder was pressed into a first green body and subjected to a first rapid sintering using ultrafast high-temperature sintering, with a peak temperature of 1600℃ and a holding time of 40 s. No external pressure was applied during the sintering process.

[0050] The first sintered body was crushed and ground, then pressed into a second green body. A second-step pressure-assisted flash sintering was performed at 60 MPa, with an apparent temperature of 900-1200℃ and a sintering time of 2 min, yielding Al-In co-doped ZnO conductive ceramics. The sample had a relative density of 96.9% and a room temperature conductivity of 1050 S / cm. Performance analysis showed that In doping promoted partial lattice matching and carrier transport, Al doping provided an efficient donor source, and co-doping balanced solid solution, grain boundary barriers, and carrier concentration.

[0051] Example 6

[0052] The material system in this embodiment is Sb-doped SnO2, with a doping composition of Sn. 1-x Sb x O 2+x / 2 Where x = 0.02. Weigh SnO2 and Sb2O5 powders according to this nominal stoichiometric ratio, or weigh SnO2 and Sb2O5 powders that can form Sb after oxidation treatment. 5+ The Sb₂O₃ powder, a dopant source, was mixed and calcined at 700℃ for 3 h. The powder was pressed into a first green compact and then directly treated with high-temperature plasma at a peak temperature of 1800℃ for 60 s, without applying external pressure during the process.

[0053] The first sintered body was crushed and ground, and the secondary powder was pressed into a second green body. A second hot-pressing sintering step was then performed under 70 MPa pressure at a sintering temperature of 1200-1500℃ for 2 h to obtain Sb-doped SnO2 conductive ceramic. The sample had a relative density of 95.5% and a room temperature conductivity of 20 S / cm. Performance analysis showed that Sb... 5+ Replace Sn 4+ It can form donor defects and increase electron concentration; high temperature and short time first treatment helps to alleviate the problems of difficult sintering of SnO2 and Sb volatilization and segregation.

[0054] Example 7

[0055] The material system in this embodiment is Sn-doped In₂O₃, i.e., an ITO system, where Sn is 5 at.% of the In sites. In₂O₃ and SnO₂ powders were weighed, mixed, and calcined at 600°C for 4 h. The powder was pressed into a first green body and subjected to ultrafast high-temperature sintering at a peak temperature of 1500°C for 50 s. No external pressure was applied during sintering, allowing Sn to dissolve in the In₂O₃ matrix.

[0056] After crushing and grinding the first sintered body, the secondary powder was pressed into a second green body. A second-step spark plasma sintering process was then performed under 60 MPa pressure at a temperature of 900-1200℃ for 10 min, yielding Sn-doped In₂O₃ conductive ceramic. The sample had a relative density of 98.2% and a room temperature conductivity of 1260 S / cm. Performance analysis showed that Sn… 4+ Replace In 3+ The formation of ITO-type donor-doped structures is achieved through a first rapid sintering process that promotes single-phase formation, followed by a second sintering process that enhances the density and uniformity required for the target-type ceramics.

[0057] Example 8

[0058] The material system in this embodiment is Nb-doped TiO2, with a doping composition of Ti. 1-x Nb x O 2-y Where x = 0.058, and y represents the oxygen vacancy content introduced by reducing atmosphere or short-term high-temperature treatment. TiO2 and Nb2O5 powders were weighed, mixed, and calcined at 800℃ for 4 h. The powder was pressed into a first green body and subjected to high-temperature plasma treatment in an inert protective atmosphere with a peak temperature of 1800℃ and a treatment time of 80 s. No external pressure was applied during the treatment.

[0059] The first sintered body was crushed and ground, and the secondary powder was pressed into a second green body. A second-step spark plasma sintering process was then performed under 80 MPa pressure at a temperature of 1000-1400℃ for 10 min, yielding Nb-doped TiO2 conductive ceramics. The sample had a relative density of 96.0% and a room temperature conductivity of 35 S / cm. Performance analysis showed that Nb… 5+ Replace Ti 4+ Electrons can be introduced, and the reducing environment and oxygen vacancies can induce Ti 3+ Related conductivity; the two-step process is advantageous for obtaining defective and dense structures in a shorter time.

[0060] Example 9

[0061] The material system in this embodiment is Si-doped Ga2O3, where Si accounts for 1 at.% of the Ga sites. Using Ga2O3 as the matrix and SiO2 or a Si-containing precursor as the dopant, the mixture is calcined at 700°C for 3 hours. The powder is pressed into a first green compact, which is then subjected to a high-temperature, short-time treatment using arc plasma. The peak temperature is 2000°C, and the treatment time is 20 seconds. No external pressure is applied during the treatment.

[0062] The first sintered body was crushed and ground, and the secondary powder was pressed into a second green body. A second hot-pressing sintering step was then performed under 50 MPa pressure at a temperature of 1000-1500℃ for 1 h, yielding Si-doped Ga2O3 conductive ceramic. The sample had a relative density of 94.8% and a room temperature conductivity of 18 S / cm. Performance analysis showed that Si can form shallow donors in Ga2O3, and short-term high-temperature treatment facilitates Si entry into Ga sites while reducing the loss of Ga-related components under prolonged high-temperature conditions.

[0063] Example 10

[0064] The material system in this embodiment is Nb-doped SrTiO3, with a doping composition of SrTi. 1-x Nb x O3, where x=0.10. SrCO3, TiO2 and Nb2O5 powders were weighed, mixed and calcined at 900℃ for 6 h, then ground and pressed into the first green body. The first rapid sintering adopted ultrafast high-temperature sintering, with a peak temperature of 1800℃ and a holding time of 60 s, and no external pressure was applied during the sintering process.

[0065] After crushing and grinding the first sintered body, the secondary powder was pressed into a second green body. A second-step spark plasma sintering process was then performed under 70 MPa pressure at a temperature of 1200-1600℃ for 10 min, yielding Nb-doped SrTiO3 conductive ceramic. The sample had a relative density of 97.5% and a room temperature conductivity of 120 S / cm. Performance analysis showed that Nb... 5+ Replace Ti 4+ It can increase electron concentration; short-time high-temperature treatment can promote the formation of perovskite phase and reduce grain coarsening caused by long-term heat preservation.

[0066] Example 11

[0067] The material system in this embodiment is La and Nb co-doped CaMnO3, where the doping amount of La relative to Ca sites is 0.05, and the doping amount of Nb relative to Mn sites is 0.05. CaCO3, MnO2, La2O3, and Nb2O5 powders were weighed, mixed, and calcined at 900℃ for 6 h. The powder was pressed into a first green compact and treated with high-temperature plasma at a peak temperature of 1700℃ for 90 s, without applying external pressure during the treatment.

[0068] After crushing and grinding the first sintered body, the secondary powder was pressed into a second green body, and then subjected to a second-step hot-pressing sintering at 60 MPa pressure, a sintering temperature of 1000-1400℃, and a sintering time of 2 h to obtain La and Nb co-doped CaMnO3 conductive ceramics. The sample had a relative density of 96.2% and a room temperature conductivity of 5 S / cm. Performance analysis showed that La... 3+ Alternative Ca 2+ and Nb 5+ Replacement of Mn 4+ Both methods allow for adjustment of carrier concentration, and short-term high-temperature treatment is beneficial for rapid formation of the perovskite phase and control of grain growth.

[0069] Example 12

[0070] The material system in this embodiment is La. 0.67 Ca 0.25 Sr 0.08 MnO3 conductive perovskite manganate ceramics. According to La... 0.67 Ca 0.25 Sr 0.08 The stoichiometric ratio of La2O3, CaCO3, SrCO3, and MnO2 powders was weighed out, mixed, and calcined at 850℃ for 6 h. The powder was then pressed into a first green compact, which was directly heated using nitrogen plasma or atmospheric plasma at a peak temperature of 1600℃ for 60 s without applying external pressure.

[0071] After the first sintered body is crushed and ground, the secondary powder is pressed into a second green body, and then subjected to a second-step hot pressing sintering at a pressure of 50 MPa, a sintering temperature of 900-1300℃, and a sintering time of 2 h to obtain La. 0.67 Ca 0.25 Sr 0.08 MnO3 conductive ceramics. The sample has a relative density of 95.8% and a room temperature conductivity of 120 S / cm. Performance analysis shows that Ca / Sr composite A-site doping can tune Mn. 3+ / Mn 4+The proportions, metal-insulator transition temperature, and temperature coefficient resistivity; the first high-temperature short-time treatment is beneficial for the rapid formation of perovskite structure and reduces the A-site composition deviation caused by long-term high-temperature sintering.

[0072] Example 13

[0073] The material system in this embodiment is La. 0.7 Sr 0.3 MnO3 conductive perovskite manganate ceramics. According to La... 0.7 Sr 0.3 La2O3, SrCO3, and MnO2 powders were weighed out in stoichiometric proportions and mixed. The mixture was then calcined at 850℃ for 6 h. The powder was pressed into a first green body and subjected to a first rapid sintering process using ultrafast high-temperature sintering. The peak temperature was 1600℃ and the holding time was 60 s. No external pressure was applied during the sintering process.

[0074] After the first sintered body was crushed and ground, the secondary powder was pressed into a second green body, and then subjected to a second-step spark plasma sintering at a pressure of 50 MPa for 10 min at a temperature of 900-1300℃. This yielded La. 0.7 Sr 0.3 MnO3 conductive ceramics. The sample has a relative density of 96.5% and a room temperature conductivity of 180 S / cm. Performance analysis shows that Sr-doped lanthanum manganate exhibits double exchange conductivity, making it suitable for magnetoresistive, temperature-sensitive, and electrode applications; the two-step method helps shorten the ceramic preparation cycle.

[0075] Example 14

[0076] The material system in this embodiment is LaNiO3 conductive perovskite nickelate ceramic. La2O3 and NiO powders were weighed according to the stoichiometric ratio of LaNiO3, mixed, and calcined at 700℃ for 3 h. The powder was pressed into a first green body, which was then directly heated by atmospheric plasma at a peak temperature of 1300℃ for 30 s without applying external pressure.

[0077] After crushing and grinding the first sintered body, the secondary powder was pressed into a second green body, and then subjected to a second-step hot-pressing sintering at 50 MPa pressure. The sintering temperature was 700-1100℃, and the sintering time was 1 h, yielding LaNiO3 conductive ceramic. The sample had a relative density of 95.0% and a room temperature conductivity of 650 S / cm. Performance analysis showed that LaNiO3 is a perovskite-type oxide with metallic conductivity characteristics, suitable for oxide electrodes and conductive functional ceramics; short-time high-temperature treatment helps reduce the formation of Ni-related second phases caused by long-term heat treatment.

[0078] As can be seen from the above embodiments, the method of the present invention is not only applicable to Ga, Al, and In single-doped ZnO systems, but also to Al-Ga, Al-In co-doped ZnO, as well as Sb-doped SnO2, Sn-doped In2O3, Nb-doped TiO2, Si-doped Ga2O3, Nb-doped SrTiO3, La / Nb co-doped CaMnO3, and perovskite-type manganate and nickelate conductive oxide ceramic systems.

Claims

1. A method for preparing a conductive oxide ceramic, characterized in that, Includes the following steps: Step 1: Mix the oxide matrix raw material and the dopant raw material according to the set stoichiometric ratio, and obtain the doped oxide mixed powder after drying, calcination and grinding; Step 2: Press the doped oxide mixed powder into a first green compact, and perform a first rapid sintering on the first green compact to make the peak temperature of the first green compact reach 1000-2500℃ and hold it for 5-120 s, so as to promote the solid solution of the doped element in the oxide matrix, inhibit the volatilization of matrix elements and doped elements under long-term holding conditions, and introduce intrinsic conductive defects and impurity conductive defects to obtain the first sintered body; Step 3: Crush and grind the first sintered body to obtain conductive powder for secondary sintering; Step 4: Press the secondary sintering powder into a second green body, and perform a second sintering on the second green body to densify it, thereby obtaining a conductive oxide ceramic. The second step of sintering is selected from one of spark plasma sintering, hot pressing sintering, and flash sintering.

2. The method for preparing a conductive oxide ceramic according to claim 1, characterized in that, The oxide matrix raw material is a dopant-compatible conductive oxide ceramic matrix, which includes ZnO, SnO2, In2O3, TiO2, Ga2O3, SrTiO3, CaMnO3, and La. 1-x A x MnO3, La 1-x A x CoO3, LaNiO3, LaCo 1-x Ni x One or more of O3, wherein A is one or more of Ca, Sr, Ag, K, and Na, 0 <x<0.5。 3. The method for preparing a conductive oxide ceramic according to claim 1, characterized in that, The dopant material is used to form one or more conductive defects in an oxide matrix, including donor defects, acceptor defects, oxygen vacancies, metal interstices, valence transition defects, A-site substitution defects, and B-site substitution defects.

4. The method for preparing a conductive oxide ceramic according to claim 1, characterized in that, In step 1, the calcination temperature is 300-900℃ and the calcination time is 1-10 h.

5. The method for preparing a conductive oxide ceramic according to claim 1, characterized in that, The first rapid sintering is selected from one of ultrafast high-temperature sintering, flash sintering and high-temperature plasma treatment.

6. The method for preparing a conductive oxide ceramic according to claim 5, characterized in that, The high-temperature plasma treatment uses electric arc plasma, atmospheric plasma, nitrogen plasma, argon plasma, or a combination thereof to directly heat the first green billet.

7. The method for preparing a conductive oxide ceramic according to claim 1, characterized in that, In step 4, the sintering pressure in the second sintering step is 10-200 MPa, the sintering time is 1 min-3 h, and the sintering temperature is 500-2200℃.

8. The method for preparing a conductive oxide ceramic according to claim 1, characterized in that, The atmosphere for the first rapid sintering in step 2 is air, oxygen, nitrogen, argon, vacuum, or a protective atmosphere containing hydrogen, carbon monoxide, or methane with a reducing gas volume fraction of not less than 0.1%. The atmosphere for sintering in the second step of step 4 is air, oxygen, nitrogen, argon, vacuum, or a protective atmosphere containing hydrogen, carbon monoxide, or methane with a reducing gas volume fraction of not less than 0.1%.

Images