CN107285769B - Preparation method of high TCR polycrystalline ceramic - Google Patents
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Abstract
The invention discloses a preparation method of high TCR polycrystalline ceramic, which is weighed according to stoichiometric ratioDissolving lanthanum nitrate, calcium nitrate and manganese nitrate in water, adding gluconic acid and ethylene glycol to obtain a mixed solution, performing magnetic stirring and heating, filtering, washing and drying, adding ethylene glycol, stirring, heating and drying again, grinding and briquetting the product, performing oxygen-enriched presintering, adding silver paste, introducing nitrogen gas for sintering, and performing oxygen-enriched sintering on the sintered product to obtain the high TCR L a0.67Ca0.33MnO3:AgxPolycrystalline ceramic L a prepared by the invention0.67Ca0.33MnO3Agx polycrystalline ceramic, with good grain uniformity and larger grain size, is more regular than polycrystalline ceramic particles obtained by solid phase reaction, L a0.67Ca0.33MnO3:Ag0.35The TCR of the polycrystalline ceramic is up to 31.6%/K at 275K, and can be applied to a heat radiation and infrared detector at near room temperature.
Description
Technical Field
The invention relates to the technical field of electronic ceramics, in particular to L a for preparing high TCR0.67Ca0.33MnO3:AgxA method for preparing polycrystalline ceramics.
Background
Perovskite-type manganese oxide L a1-xAxMnO3(A = Ca, Ba, Sr, Pb …) because of its unusual magnetic and transport behavior (e.g., giant magnetoresistance effect CMR and laser induced thermo-electric voltage effect L IV), and Curie temperature (T)c) Near room temperature metal-insulator transition temperature (T)p) And high Temperature Coefficient of Resistance (TCR), so that the perovskite manganese oxide can be widely applied to devices such as photoelectric fast devices, magnetic sensors, spin valve devices, ultra-giant magneto-resistance bolometers and the like. However, a temperature sensitive device such as an infrared detector of an ultragiant magnetoresistance bolometer or the like is required to have high sensitivity, and therefore, a manganese oxide material used for preparing the detector is required to obtain a high TCR value and a near room temperature Tk（TkThe TCR transformation point temperature is usually equal to the metal-insulation transformation temperature TpAre located very close).
Research shows that when the doping amount x is=1/3, the double exchange effect of the system is strongest, and the system has high TCR (more than 10 percent) and metal-insulation state transition temperature T close to room temperaturep(about 266K) in 2007, v.p.s, Awana et al, using a conventional solid phase method, obtained L a with Ag doping x =0.4 (wt%),0.67Ca0.33MnO3agx polycrystalline composite material with TCR =15% K-1，Tk=270.5 k. and undoped L a0.67Ca0.33MnO3In contrast, L a0.67Ca0.33MnO3TCR and T of Agx MaterialkA significant improvement is obtained. However, the solid phase method has disadvantages of large energy consumption, low efficiency, insufficiently fine powder, and easy contamination with impurities.
Disclosure of Invention
The invention aims to provide a preparation method of high TCR polycrystalline ceramic, and TCR obtained by the method is up to 31.6 percent K-1The method has the advantages of simple process, easy repetition and low cost.
The invention is realized by the following technical scheme that the high TCR L a0.67Ca0.33MnO3:AgxThe preparation method of the polycrystalline ceramic comprises the following steps;
(1) lanthanum nitrate, calcium nitrate and manganese nitrate are weighed according to the stoichiometric ratio and dissolved in water, and the mass of the cation in the solution is as follows: the method comprises the following steps of weighing gluconic acid according to the proportion of gluconic acid radical ions =1: 2-1: 4, adding the gluconic acid into a solution, and adding ethylene glycol to obtain a mixed solution;
(2) magnetically stirring the mixed solution obtained in the step (1) at 80-90 ℃ for 2-3 h, and carrying out full chemical reaction on the raw materials in the heating and stirring process to obtain brown yellow sol;
(3) filtering and washing the brown yellow sol obtained in the step (2), drying by vacuum microwave, adding glycol and water, and magnetically stirring for 1.5-2.5 h at the temperature of 80-90 ℃ to obtain high-purity complex gel;
(4) carrying out oxygen-enriched microwave drying on the high-purity complex gel obtained in the step (3), wherein the oxygen pressure is 0.05-0.1 MPa, the drying temperature is 145-160 ℃, the drying time is 8-10 h, and grinding the dried product to obtain powder;
(5) tabletting the powder obtained in the step (4) by adopting a pressure intensity of 15-17 MPa to obtain a ceramic block, carrying out oxygen-enriched pre-sintering, heating to 200 ℃, 400 ℃ and 500 ℃ at a speed of 3-5 ℃/min, respectively preserving heat for 0.5h at each temperature, heating to 600-800 ℃ at a speed of 2-4 ℃/min, preserving heat for 4-6 h, and cooling along with a furnace;
(6) according to L a0.67Ca0.33MnO3:AgxIn a stoichiometric ratio of (b), whereinx= 0.3-0.4, adding liquefied silver paste into the product obtained in the step (5), introducing nitrogen under the pressure of 0.04-0.1 MPa, and sintering at 500-600 ℃ for 3-5 h;
(7) cooling the product obtained in the step (6) to room temperature along with a furnace, vacuumizing, introducing oxygen, heating to 980-1100 ℃ at the speed of 3-5 ℃/min, and performing oxygen-enriched sintering for 12-24 hours to obtain L a0.67Ca0.33MnO3:AgxPolycrystalline ceramic blocks.
Preferably, quantitative filter paper with the membrane diameter of 1-3 μm is adopted for filtering and washing in the step (3), the filtering and washing are carried out until the filtrate is neutral, and ions which do not undergo a complexation reaction are removed by filtering, so that high-purity complex sol which is completely complexed and does not have ion mismatch is obtained; the vacuum degree of the vacuum microwave drying is 1-1.5 MPa, the vacuum degree is 80-90 ℃, the drying is carried out for 1-2 hours, the vacuum drying is used for isolating air and preventing chemical reaction from generating impurities in the drying process, and because the high-purity complex sol is a viscous semi-solid state, the high-purity complex sol needs microwave heating to be heated uniformly and prevent nonuniform complexation caused by nonuniform heating.
Preferably, the ethylene glycol and the water in the step (3) are added according to the volume ratio of the ethylene glycol to the water of 1: 2-5.
Preferably, the oxygen pressure of the oxygen-enriched pre-sintering in the step (5) is 0.04-0.1 MPa, the oxygen introducing time is the time required by the pre-sintering, oxygen can be introduced as a protective gas due to higher powder purity, and the powder is fully combusted into a sintering phase in the sintering process.
Preferably, in the step (7), the oxygen-enriched burning oxygen pressure is 0.06-0.12 MPa, the oxygen introducing time is the time required by the final burning, silver is doped in the pre-sintered ceramic in the sintering process, and because the silver is fully reacted with the ceramic block material in a closed furnace, oxygen is introduced, so that a sample can be fully combusted, the double exchange effect is promoted to be carried out, and a better ceramic block material is obtained.
Compared with the prior art, the invention has the beneficial effects and advantages that:
l a prepared by the method of the invention0.67Ca0.33MnO3:AgxThe polycrystalline ceramic has good grain uniformity and hasThe grain size is larger, and is more regular than polycrystalline ceramic particles obtained by solid phase reaction; moreover, the product has up to 31.6% K-1The TCR and Tk (275K) close to room temperature can be applied to a thermal radiation and infrared detector close to room temperature.
Drawings
FIG. 1 shows L a obtained in example 10.67Ca0.33MnO3:Ag0.3TCR profile of polycrystalline ceramic;
FIG. 2 shows L a obtained in example 20.67Ca0.33MnO3:Ag0.35TCR profile of polycrystalline ceramic;
FIG. 3 shows L a obtained in example 30.67Ca0.33MnO3:Ag0.4TCR profile of polycrystalline ceramic.
Detailed Description
The invention will be described in detail below with reference to the drawings and examples, but the scope of the invention is not limited thereto.
Example 1
This embodiment is a high TCR L a0.67Ca0.33MnO3:AgxThe preparation method of the polycrystalline ceramic specifically comprises the following steps:
(1) 2.9011g of lanthanum nitrate hydrate (L a (NO) calculated according to stoichiometric ratio3)3·6H2O), 0.7793g of hydrated calcium nitrate (Ca (NO)3)2·4H2O) and 3.579g of manganese nitrate solution (50% by mass of Mn (NO)3)2Solution) medicine, dissolving the medicine in 300m L high-purity deionized water to obtain a nitrate cation solution, weighing gluconic acid according to the ratio of the amount of cations to the amount of gluconic acid radical ions in the solution =1: 3, adding the gluconic acid into the nitrate cation solution, and adding 10m L ethylene glycol to obtain a mixed solution;
(2) heating and evaporating the mixed solution obtained in the step (1) by using a magnetic stirrer, wherein the heating temperature is 85 ℃, the heating and stirring time is 2.5 hours, and the raw materials are subjected to full chemical reaction in the heating and stirring process to obtain brown yellow sol;
(3) filtering and washing the brown yellow sol obtained in the step (2) by using 1 mu m quantitative filter paper until filtrate is neutral, filtering and removing ions which are not subjected to complexing reaction to obtain high-purity complex sol which is completely complexed and has no ion mismatching, then performing vacuum microwave drying, wherein the vacuum drying is to isolate air and prevent chemical reaction from generating impurities in the drying process, because the high-purity complex sol is a viscous semi-solid state, microwave heating is needed to ensure that the high-purity complex sol is uniformly heated and nonuniform complexation caused by nonuniform heating is prevented, the set drying vacuum degree is 1MPa, the drying temperature is 90 ℃, the drying time is 1.5h, then pouring 50m L high-purity deionized water and 10m L ethylene glycol, performing magnetic stirring and heating, the heating temperature is 85 ℃, the heating and stirring time is 2h to obtain high-purity complex gel, and the high-purity complex gel is uniformly dissolved and dispersed by adding the ethylene glycol and the deionized water, and the high purity and the;
(4) carrying out oxygen-enriched microwave drying on the high-purity complex gel obtained in the step (3) to obtain black high-purity dry gel, wherein the oxygen pressure is 0.05MPa, the drying temperature is 150 ℃, the drying time is 9 hours, so that the black high-purity dry gel is subjected to self-propagating combustion, and grinding the dried product to obtain high-purity ceramic powder;
(5) and (4) tabletting the high-purity ceramic powder obtained in the step (4) by adopting a pressure intensity of 15MPa to obtain a ceramic block, namely vacuumizing the interior of a sintering furnace, introducing oxygen to perform oxygen-enriched pre-sintering, wherein the oxygen pressure is 0.04MPa, the temperature is raised to 200 ℃ at the speed of 4 ℃/min in the pre-sintering stage and is kept for 0.5h, the temperature is raised to 400 ℃ at the same speed and is kept for 0.5h, the temperature is raised to 500 ℃ at the same speed and is kept for 0.5h, the temperature is raised to 600 ℃ at the pre-sintering end point at the speed of 3 ℃/min, the temperature is kept for 4h, and furnace0.67Ca0.33MnO3And the cation raw material is not lost in the whole process;
(6) placing the product obtained in the step (5) in a built-in container of a sintering furnace according to L a0.67Ca0.33MnO3:AgxIs added to the liquefied silver paste in a stoichiometric ratio, whereinxClosing the sintering furnace, introducing nitrogen, closing the port of the built-in container, and sintering at 500 ℃ for 5 hours under the nitrogen pressure of 0.1 MPa;
(7) obtained in the step (6)Cooling the product to room temperature along with the furnace, opening a built-in container port, vacuumizing, extracting nitrogen in the furnace, introducing oxygen with the oxygen pressure of 0.06MPa, heating to the final firing end point temperature of 980 ℃ at the speed of 4 ℃/min, carrying out oxygen-enriched sintering for 24h, cooling to room temperature along with the furnace, introducing oxygen in a closed furnace to ensure that silver and ceramic blocks are fully reacted, so that a sample can be fully combusted, and the double exchange effect is promoted to be carried out, thereby finally obtaining the L a of the high TCR0.67Ca0.33MnO3:Ag0.3Polycrystalline ceramic blocks.
L a obtained in this example0.67Ca0.33MnO3:Ag0.3The polycrystalline ceramic has smaller powder granularity, better uniformity and high density, and the TCR curve is shown in figure 1, and the highest TCR is 29 percent.
Example 2
This embodiment is a high TCR L a0.67Ca0.33MnO3:AgxThe preparation method of the polycrystalline ceramic specifically comprises the following steps:
(1) 8.7035g of lanthanum nitrate hydrate (L a (NO) calculated according to stoichiometric ratio3)3·6H2O), 2.3379g of hydrated calcium nitrate (Ca (NO)3)2·4H2O) and 10.737g of manganese nitrate solution (50% by mass of Mn (NO)3)2Solution), dissolving the medicine in 500m L high-purity deionized water to obtain a nitrate cation solution, weighing gluconic acid according to the ratio of the amount of cations to the amount of gluconic acid radical ions in the solution =1: 4, adding the gluconic acid into the nitrate cation solution, and adding 30m L ethylene glycol to obtain a mixed solution;
(2) heating and evaporating the mixed solution obtained in the step (1) by using a magnetic stirrer, wherein the heating temperature is 90 ℃, the heating time is 2 hours, and the raw materials are subjected to full chemical reaction in the heating and stirring process to obtain brown yellow sol;
(3) filtering and washing the brown yellow sol obtained in the step (2) by using 3 mu m quantitative filter paper until filtrate is neutral, filtering and removing ions which are not subjected to complexation reaction to obtain high-purity complex sol which is completely complexed and has no ion mismatch, then performing vacuum microwave drying, wherein the vacuum drying is to isolate air and prevent chemical reaction from generating impurities in the drying process, because the high-purity complex sol is a viscous semi-solid state, microwave heating is needed to ensure that the high-purity complex sol is uniformly heated and nonuniform complexation caused by nonuniform heating is prevented, the set drying vacuum degree is 1.5MPa, the drying temperature is 85 ℃, the drying time is 1h, then pouring 100m L high-purity deionized water and 50m L glycol water, performing magnetic stirring and heating, the heating temperature is 90 ℃, the heating and stirring time is 1.5h, obtaining high-purity complex gel, and adding glycol and deionized water to ensure that the high-purity complex sol is uniformly dispersed and the uniformity of the complex gel is maintained;
(4) carrying out oxygen-enriched microwave drying on the high-purity complex gel obtained in the step (3) to obtain black high-purity dry gel, wherein the oxygen pressure is 0.1MPa, the drying temperature is 160 ℃, the drying time is 10 hours, so that the black high-purity dry gel is subjected to self-propagating combustion, and grinding the dried product to obtain high-purity ceramic powder;
(5) carrying out tabletting on the high-purity ceramic powder obtained in the step (4) by adopting a pressure intensity of 17MPa to obtain a ceramic block, namely vacuumizing the interior of a sintering furnace, introducing oxygen, enriching oxygen, and presintering, wherein the oxygen pressure is 0.05MPa, the presintering stage is carried out, the temperature is raised to 200 ℃ at the speed of 3 ℃/min and is kept for 0.5h, the temperature is raised to 400 ℃ at the same speed and is kept for 0.5h, then the temperature is raised to 500 ℃ at the same speed and is kept for 0.5h, the temperature is raised to 800 ℃ at the presintering end point at the speed of 2 ℃/min and is kept;
(6) placing the product obtained in the step (5) in a built-in container of a sintering furnace according to L a0.67Ca0.33MnO3:AgxIs added to the liquefied silver paste in a stoichiometric ratio, whereinxClosing the sintering furnace, introducing nitrogen, closing the port of the built-in container, and sintering at 550 ℃ for 4 hours under the nitrogen pressure of 0.05 Mpa;
(7) cooling the product obtained in the step (6) to room temperature along with the furnace, opening a built-in container port, vacuumizing, extracting nitrogen in the furnace, then introducing oxygen with the oxygen pressure of 0.07MPa, heating to the final firing end point temperature of 1000 ℃ at the speed of 3 ℃/min, carrying out oxygen-enriched sintering for 12h, cooling to room temperature along with the furnace, wherein in the sealed furnace, in order to ensure that silver and ceramic blocks are fully reacted,oxygen is introduced to ensure that the sample can be fully combusted, the double exchange effect is promoted to be carried out, and finally L a with high TCR is obtained0.67Ca0.33MnO3:Ag0.35Polycrystalline ceramic blocks.
L a obtained in this example0.67Ca0.33MnO3:Ag0.35The polycrystalline ceramic has smaller powder granularity, better uniformity and high density, the TCR curve of the polycrystalline ceramic is shown in figure 2, and the highest TCR is 31.6 percent.
Example 3
This embodiment is a high TCR L a0.67Ca0.33MnO3:AgxThe preparation method of the polycrystalline ceramic specifically comprises the following steps:
(1) 5.8023g of lanthanum nitrate hydrate (L a (NO) calculated according to stoichiometric ratio3)3·6H2O), 1.5587g of hydrated calcium nitrate (Ca (NO)3)2·4H2O) and 7.158g of manganese nitrate solution (50% by mass of Mn (NO)3)2Solution), dissolving the drug in 350m L high-purity deionized water to obtain a nitrate cation solution, weighing gluconic acid according to the ratio of the amount of cations to the amount of gluconic acid radical ions in the solution =1:2, adding 15m L ethylene glycol into the cation solution to obtain a mixed solution;
(2) heating and evaporating the mixed solution obtained in the step (1) by using a magnetic stirrer, wherein the heating temperature is 80 ℃, the heating time is 3 hours, and the raw materials are subjected to full chemical reaction in the heating and stirring process to obtain brown yellow sol;
(3) filtering and washing the brown yellow sol obtained in the step (2) by using 2 mu m quantitative filter paper until filtrate is neutral, filtering and removing ions which are not subjected to complexing reaction to obtain high-purity complex sol which is completely complexed and has no ion mismatch, then performing vacuum microwave drying, wherein the vacuum drying is to isolate air and prevent chemical reaction from generating impurities in the drying process, because the high-purity complex sol is a viscous semi-solid state, the high-purity complex sol is heated uniformly by microwave heating and prevent nonuniform complexing caused by nonuniform heating, the set drying vacuum degree is 1.2MPa, the drying temperature is 80 ℃, the drying time is 2 hours, then pouring 90m L high-purity deionized water and 30m L ethylene glycol, performing magnetic stirring and heating, the heating temperature is 80 ℃, the heating and stirring time is 2.5 hours, obtaining high-purity complex gel, and adding the ethylene glycol and the deionized water to dissolve and disperse the high-purity complex gel uniformly and keeping the high purity and the uniformity of the complex gel;
(4) carrying out oxygen-enriched microwave drying on the high-purity complex gel obtained in the step (3) to obtain black high-purity dry gel, wherein the oxygen pressure is 0.08MPa, the drying temperature is 145 ℃, the drying time is 8 hours, so that the black high-purity dry gel is subjected to self-propagating combustion, and grinding the dried product to obtain high-purity ceramic powder;
(5) carrying out tabletting on the high-purity ceramic powder obtained in the step (4) by adopting a pressure intensity of 16MPa to obtain a ceramic block, namely vacuumizing the interior of a sintering furnace, introducing oxygen to carry out oxygen-enriched pre-sintering, wherein the oxygen pressure is 0.1MPa, the temperature is raised to 200 ℃ at the speed of 5 ℃/min in the pre-sintering stage and is kept for 0.5h, the temperature is raised to 400 ℃ at the same speed and is kept for 0.5h, then the temperature is raised to 500 ℃ at the same speed and is kept for 0.5h, the temperature is raised to 700 ℃ at the pre-sintering end point at the speed of 4 ℃/min and is kept for 5 h;
(6) placing the product obtained in the step (5) in a built-in container of a sintering furnace according to L a0.67Ca0.33MnO3:AgxIs added to the liquefied silver paste in a stoichiometric ratio, whereinxClosing the sintering furnace, introducing nitrogen, closing the port of the built-in container, and sintering at 600 ℃ for 3 hours under the nitrogen pressure of 0.04 Mpa;
(7) cooling the product obtained in the step (6) to room temperature along with the furnace, opening a built-in container port, vacuumizing, extracting nitrogen in the furnace, then introducing oxygen, setting the oxygen pressure to be 0.12MPa, heating to the final firing end point temperature of 1100 ℃ at the speed of 5 ℃/min, carrying out oxygen-enriched sintering for 20 hours, and finally cooling to room temperature along with the furnace0.67Ca0.33MnO3:Ag0.4Polycrystalline ceramic blocks.
L a obtained in this example0.67Ca0.33MnO3:Ag0.4The polycrystalline ceramic has smaller powder granularity, better uniformity and high density, the TCR curve of the polycrystalline ceramic is shown in figure 1, and the highest TCR is 30.7 percent.
Claims (5)
1. A preparation method of high TCR polycrystalline ceramic is characterized by comprising the following steps:
(1) press L a0.67Ca0.33MnO3The lanthanum nitrate, the calcium nitrate and the manganese nitrate are weighed according to the stoichiometric ratio and dissolved in water, gluconic acid is weighed and added into the solution according to the proportion that the quantity of cations to the quantity of gluconic acid radical ions in the solution is =1: 2-1: 4, and then ethylene glycol is added to obtain a mixed solution;
(2) magnetically stirring the mixed solution obtained in the step (1) at the temperature of 80-90 ℃ for 2-3 h to obtain brown yellow sol;
(3) filtering and washing the brown yellow sol obtained in the step (2), drying by vacuum microwave, adding glycol and water, and magnetically stirring for 1.5-2.5 h at the temperature of 80-90 ℃ to obtain complex gel;
(4) carrying out oxygen-enriched microwave drying on the complex gel obtained in the step (3), wherein the oxygen pressure is 0.05-0.1 MPa, the drying temperature is 145-160 ℃, the drying time is 8-10 h, and grinding the dried product to obtain powder;
(5) tabletting the powder obtained in the step (4) by adopting a pressure intensity of 15-17 MPa to obtain a ceramic block, carrying out oxygen-enriched pre-sintering, heating to 200 ℃, 400 ℃ and 500 ℃ at a speed of 3-5 ℃/min, respectively preserving heat for 0.5h at each temperature, heating to 600-800 ℃ at a speed of 2-4 ℃/min, preserving heat for 4-6 h, and cooling along with a furnace;
(6) according to L a0.67Ca0.33MnO3:AgxIn a stoichiometric ratio of (b), whereinx= 0.3-0.4, adding liquefied silver paste into the product obtained in the step (5), and sintering at 500-600 ℃ for 3-5 h under the nitrogen pressure of 0.04-0.1 Mpa;
(7) cooling the product obtained in the step (6) to room temperature along with a furnace, vacuumizing, introducing oxygen, heating to 980-1100 ℃ at the speed of 3-5 ℃/min, and performing oxygen-enriched sintering for 12-24 hours to obtain L a0.67Ca0.33MnO3:AgxPolycrystalline ceramic blocks.
2. The preparation method of the high TCR polycrystalline ceramic according to claim 1, wherein the filtration and washing in step (3) is performed by quantitative filter paper with a membrane diameter of 1-3 μm, and the filtration and washing is performed until the filtrate is neutral; the vacuum degree of the vacuum microwave drying is 1-1.5 MPa, and the drying is carried out for 1-2 h at the temperature of 80-90 ℃.
3. The method for preparing a high TCR polycrystalline ceramic according to claim 1 wherein the ethylene glycol and water of step (3) are added in a volume ratio of ethylene glycol to water of 1:2 to 5.
4. The method for preparing a high TCR polycrystalline ceramic according to claim 1 wherein the oxygen pressure of the oxygen-rich pre-sintering of step (5) is 0.04 to 0.1 MPa.
5. The method for preparing a high TCR polycrystalline ceramic according to claim 1 wherein the oxygen pressure of the oxygen-rich sintering of step (7) is 0.06 to 0.12 MPa.
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| CN103449801A (en) * | 2013-08-12 | 2013-12-18 | 昆明理工大学 | Preparation method of high-TCR (temperature coefficient of resistance) polycrystalline ceramic |
| CN104211399A (en) * | 2014-07-24 | 2014-12-17 | 昆明理工大学 | Preparation method of polycrystalline target material with controllable temperature coefficient of resistance (TCR) |
| CN105321642A (en) * | 2014-07-31 | 2016-02-10 | 中国振华集团云科电子有限公司 | Preparation method of high-TCR low square resistance linear NTC resistance paste |
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| CN103449801A (en) * | 2013-08-12 | 2013-12-18 | 昆明理工大学 | Preparation method of high-TCR (temperature coefficient of resistance) polycrystalline ceramic |
| CN104211399A (en) * | 2014-07-24 | 2014-12-17 | 昆明理工大学 | Preparation method of polycrystalline target material with controllable temperature coefficient of resistance (TCR) |
| CN105321642A (en) * | 2014-07-31 | 2016-02-10 | 中国振华集团云科电子有限公司 | Preparation method of high-TCR low square resistance linear NTC resistance paste |
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