Preparation method of a negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 ​

Abstract

The present invention discloses a preparation method of a negative temperature coefficient thermistor material Sr8Ti7S 21 to solve the problems of difficult preparation and high resistance of current thermistor materials. The preparation method includes the following steps: using SrTiO3 powder as a raw material, performing a sulfidation reaction to obtain Sr8Ti7S 21 powder; hot-pressing the obtained Sr8Ti7S 21 powder to obtain a Sr8Ti7S 21 green body; performing high-temperature sintering on the obtained Sr8Ti7S 21 green body, and then a negative temperature coefficient thermistor material Sr8Ti7S 21 can be obtained. Based on different sintering temperatures, the present invention can obtain a negative temperature coefficient thermistor Sr8Ti7S 21 with a room temperature resistivity of 0.7 - 15.9 Ω·cm, which shows a good resistance-temperature correlation and has good application prospects in the field of temperature detection and other fields.

Description

Technical Field

[0001] The present invention belongs to the field of preparation methods of novel electronic functional materials, and particularly relates to a preparation method of a negative temperature coefficient thermistor Sr 8 Ti 7 S 21 . Background Art

[0002] A negative temperature coefficient thermistor is a special electronic functional material, and its characteristic lies in that its resistivity decreases exponentially with temperature. The application fields of negative temperature coefficient thermistors include: temperature measurement, temperature compensation and regulation, surge current resistance, etc.

[0003] Negative temperature coefficient thermistors mainly include spinel structure and perovskite structure materials. With the diversification of application scenarios, the requirements for negative temperature coefficient thermistor materials are becoming increasingly complex and diversified. Existing oxide negative temperature coefficient thermistor materials have problems such as too high resistance and difficult sintering. For example, in Chinese invention patent CN112830770, it is mentioned that the resistance of the oxide thermistor is greater than 10000 Ω·cm, the grinding time is greater than 4 hours, and the sintering time is greater than 8 hours. The above situation has prompted researchers to explore new negative temperature coefficient thermistor materials with low resistance, high stability, and higher sensitivity.

[0004] Compared with metal-oxygen chemical bonds, metal-sulfur chemical bonds have stronger covalency, and the sulfur 3p orbitals that make up the valence band top in the compound are higher than the oxygen 2p orbitals. The above characteristics make it easier to form narrow-bandgap compounds in sulfides, and their energy band structures are more conducive to conduction. In addition, based on the unique perovskite structure, researchers expect that sulfide perovskite materials have excellent carrier transport properties, high stability, and better sintering and processing characteristics, and are expected to become excellent negative temperature coefficient thermistor materials. Summary of the Invention

[0005] The main object of the present invention is: aiming at the problems of too high resistance and difficult sintering existing in traditional negative temperature coefficient thermistor materials, to propose a high-efficiency and fast preparation method of a negative temperature coefficient thermistor Sr 8 Ti 7 S 21 , and the prepared Sr 8 Ti 7 S 21 material exhibits advantages such as negative temperature coefficient, low resistivity, and good stability.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] Step S1, using SrTiO 3 as a raw material, performing a sulfidation reaction to obtain Sr8 Ti 7 S 21 Powder

[0008] Step S2: Subject the Sr 8 Ti 7 S 21 powder obtained in Step S1 to hot pressing to obtain a Sr 8 Ti 7 S 21 green body

[0009] Step S3: Subject the Sr 8 Ti 7 S 21 green body obtained in Step S2 to high-temperature sintering to obtain a negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0010] In the said Step S1, the specific steps for preparing the Sr 8 Ti 7 S 21 powder are as follows:

[0011] Step S1-1: Weigh a certain amount of SrTiO 3 raw material powder, put the SrTiO 3 raw material powder into a quartz boat, and place the quartz boat carrying the SrTiO 3 raw material powder in a tube furnace

[0012] Step S1-2: To avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa

[0013] Step S1-3: Introduce a sulfiding gas into the above tube furnace. Here, the sulfiding gas can be CS 2 or H 2 S

[0014] Step S1-4: Adjust the air pressure in the above tube furnace to 30 Pa, heat the tube furnace to 1000 °C, hold for 1 h to complete the sulfiding reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the powder, which is the Sr 8 Ti 7 S 21 powder

[0015] In the said Step S2, the hot pressing process of the Sr 8 Ti 7 S 21 green body is as follows:

[0016] Step S2-1: Weigh a certain amount of Sr8 Ti 7 S 21 Put the powder into a graphite mold.

[0017] Step S2-2: Put the above graphite mold into a tablet press and apply pressure to the mold until the pressure reaches 50 MPa.

[0018] Step S2-3: Use a high-frequency hot press to rapidly heat up the graphite mold to 400 °C, hold for 2 min, then cool down to room temperature, and demold the graphite mold to obtain the Sr 8 Ti 7 S 21 green body.

[0019] In the said step S3, the high-temperature sintering step of the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 is as follows:

[0020] Step S3-1: Put the Sr 8 Ti 7 S 21 green body obtained in step S2 into a tube furnace.

[0021] Step S3-2: To avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa.

[0022] Step S3-3: Introduce CS 2 gas into the above tube furnace to form a reducing protective gas atmosphere to avoid the oxidation of the Sr 8 Ti 7 S 21 green body during high-temperature sintering.

[0023] Step S3-4: Adjust the air pressure in the above tube furnace to 30 Pa, heat up the tube furnace to the set sintering temperature, hold for 1 h to complete high-temperature sintering, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the thermistor Sr 8 Ti 7 S 21 .

[0024] Based on the above preparation method, the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 can be prepared.

[0025] The technical principle of the present invention lies in: making full use of the sulfide perovskite Sr 8 Ti 7 S 21Good carrier transport performance enables a lower resistance; thanks to the sulfide perovskite Sr 8 Ti 7 S 21 Good processability allows the use of the method of "hot-pressing green body - high-temperature sintering" to shorten the sintering time to as low as 1 h, realizing the preparation of the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] Using commercial, easily available, and inexpensive raw materials SrTiO 3 and CS 2 , H 2 S, etc., realizes the preparation of Sr 8 Ti 7 S 21 powder; based on Sr 8 Ti 7 S 21 powder, hot-pressing means are adopted to obtain Sr 8 Ti 7 S 21 green body; based on Sr 8 Ti 7 S 21 green body, sintering is carried out under the protection of a reducing atmosphere to obtain Sr 8 Ti 7 S 21 thermistor material with good performance. Compared with the traditional negative temperature coefficient materials prepared, the technical solution of the present invention is simple, fast, and efficient, can be compatible with the existing processes, and is convenient for batch production. The prepared Sr 8 Ti 7 S 21 thermistor material has an obvious negative temperature coefficient in the range of 30 - 150 °C, with stable performance and good consistency, and can be applied to fields such as temperature sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings described herein are used to disclose a further understanding of the present invention, constitute a part of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 is the flowchart for the preparation of the Sr 8 Ti 7 S 21 thermistor material in the present invention;

[0030] Figure 2 Sr prepared in Example 1 of the present invention 8 Ti 7 S 21 X-ray diffraction pattern of the thermistor ( Figure 2 a), X-ray energy dispersive spectrum ( Figure 2 b), X-ray photoelectron spectrum ( Figure 2 c), and the resistance-temperature characteristic curve of the Sr 8 Ti 7 S 21 thermistor material ( Figure 2 d);

[0031] Figure 3 Sr prepared in Example 2 of the present invention 8 Ti 7 S 21 resistance-temperature characteristic curve of the thermistor material;

[0032] Figure 4 Sr prepared in Example 3 of the present invention 8 Ti 7 S 21 resistance-temperature characteristic curve of the thermistor material;

[0033] Figure 5 Sr prepared in Example 4 of the present invention 8 Ti 7 S 21 resistance-temperature characteristic curve of the thermistor material;

[0034] Figure 6 Sr prepared in Example 5 of the present invention 8 Ti 7 S 21 resistance-temperature characteristic curve of the thermistor material. Detailed implementation manners

[0035] The main object of the present invention is to provide a preparation method of a negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 To make the object, technical solution and effect of the present invention clearer and more definite, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Example 1

[0037] Step S1, Sr 8 Ti 7 S 21 Powder preparation: Weigh a certain amount of SrTiO3 Raw material powder, SrTiO 3 Put the raw material powder into a quartz boat, and place the quartz boat carrying the SrTiO 3 raw material powder in a tube furnace; to avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa; introduce a sulfurizing gas into the above tube furnace, and the sulfurizing gas here is CS 2 ; adjust the air pressure in the above tube furnace to 30 Pa, heat the tube furnace to 1000 °C, keep it for 1 h, complete the sulfurization reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the powder, which is Sr 8 Ti 7 S 21 powder.

[0038] Step S2, Sr 8 Ti 7 S 21 Green body preparation: Weigh a certain amount of Sr 8 Ti 7 S 21 powder, and put it into a graphite mold; put the above graphite mold into a tablet press, apply pressure to the mold to make the pressure reach 50 MPa; use a high-frequency hot press to quickly heat the graphite mold to 400 °C, keep it warm for 2 min, then cool it to room temperature, and demold the graphite mold to obtain Sr 8 Ti 7 S 21 green body;

[0039] Step S3, preparation of thermistor Sr 8 Ti 7 S 21 Preparation: Put the Sr 8 Ti 7 S 21 green body obtained in step S2 into a tube furnace; to avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa; introduce CS 2 gas into the above tube furnace to form a reducing protective gas atmosphere to avoid Sr 8 Ti 7 S 21 green body from being oxidized during high-temperature sintering; adjust the air pressure in the above tube furnace to 30 Pa, heat the tube furnace to the set sintering temperature of 1100 °C, keep it for 1 h, complete the high-temperature sintering reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the thermistor material Sr 8 Ti 7 S 21 .

[0040] The above preparation method can be used to prepare the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0041] As Figure 1 shown, the preparation process and experimental scheme of the thermistor material Sr 8 Ti 7 S 21 are described.

[0042] As Figure 2 shown in a, the X-ray diffraction pattern of the thermistor material Sr 8 Ti 7 S 21 matches well with the standard card (source: ICDD database, card number: 04-019-3107), proving that the above experimental scheme can obtain pure-phase Sr 8 Ti 7 S 21 ; as Figure 2 shown in b, the X-ray energy dispersive spectrum of the thermistor material Sr 8 Ti 7 S 21 shows that it contains elements such as Sr, Ti, and S as expected; similarly, as Figure 2 shown in c, the X-ray photoelectron spectrum of the thermistor material Sr 8 Ti 7 S 21 also supports that it contains elements such as Sr, Ti, and S as expected; as Figure 2 shown in d, the ln(ρ)~1000 / T of the thermistor material Sr 8 Ti 7 S 21 shows a good linear relationship and can achieve an accurate temperature-resistance sensing function. Its room temperature resistance is 0.8 Ω·cm.

[0043] Example 2

[0044] Step S1, Sr 8 Ti 7 S 21 Powder preparation: Weigh a certain amount of SrTiO 3 raw material powder, put the SrTiO 3 raw material powder into a quartz boat, and place the quartz boat carrying the SrTiO 3 raw material powder in a tube furnace; to avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa; introduce a sulfide gas into the above tube furnace, and the sulfide gas here is CS 2; Adjust the air pressure in the above tubular furnace to 30 Pa, heat the tubular furnace to 1000 °C, hold for 1 h to complete the sulfidation reaction, then lower the temperature of the tubular furnace to room temperature, open the tubular furnace, and take out the powder, which is Sr 8 Ti 7 S 21 powder.

[0045] Step S2, Sr 8 Ti 7 S 21 Green body preparation: Weigh a certain amount of Sr 8 Ti 7 S 21 powder, and put it into a graphite mold; put the above graphite mold into a tablet press, apply pressure to the mold to make the pressure reach 50 MPa; use a high-frequency hot press to quickly heat the graphite mold to 400 °C, hold for 2 min, then cool to room temperature, and demold the graphite mold to obtain Sr 8 Ti 7 S 21 green body;

[0046] Step S3, preparation of the thermistor Sr 8 Ti 7 S 21 Preparation: Put the Sr 8 Ti 7 S 21 green body obtained in Step S2 into a tubular furnace; to avoid the influence of other impurities in the air, evacuate the tubular furnace to make the background vacuum lower than 0.1 Pa; introduce CS 2 gas into the above tubular furnace to form a reducing protective gas atmosphere to avoid Sr 8 Ti 7 S 21 green body from oxidizing during the high-temperature sintering process; adjust the air pressure in the above tubular furnace to 30 Pa, heat the tubular furnace to the set sintering temperature of 1000 °C, hold for 1 h to complete the high-temperature sintering reaction, then lower the temperature of the tubular furnace to room temperature, open the tubular furnace, and take out the thermistor material Sr 8 Ti 7 S 21 .

[0047] The above preparation method can prepare the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0048] As Figure 3 shown, the thermistor material Sr 8 Ti 7 S 21The ln(ρ)~1000 / T shows a good linear relationship and can achieve an accurate temperature-resistance sensing function. Its room temperature resistance is 2.8 Ω·cm.

[0049] Example 3

[0050] Step S1, Sr 8 Ti 7 S 21 Powder preparation: Weigh a certain amount of SrTiO 3 raw material powder. Put the SrTiO 3 raw material powder into a quartz boat, and place the quartz boat carrying the SrTiO 3 raw material powder in a tube furnace; to avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa; introduce a sulfurization gas into the above tube furnace. Here, the sulfurization gas is CS 2 ; adjust the air pressure in the above tube furnace to 30 Pa, heat the tube furnace to 1000 °C, keep it for 1 h to complete the sulfurization reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the powder, which is Sr 8 Ti 7 S 21 powder.

[0051] Step S2, Sr 8 Ti 7 S 21 Green body preparation: Weigh a certain amount of Sr 8 Ti 7 S 21 powder and put it into a graphite mold; put the above graphite mold into a tablet press and apply pressure to the mold to make the pressure reach 50 MPa; use a high-frequency hot press to quickly heat the graphite mold to 400 °C, keep it warm for 2 min, then cool it to room temperature, and demold the graphite mold to obtain Sr 8 Ti 7 S 21 green body;

[0052] Step S3, preparation of thermistor Sr 8 Ti 7 S 21 Prepare: Put the Sr 8 Ti 7 S 21 green body obtained in step S2 into a tube furnace; to avoid the influence of other impurities in the air, evacuate the tube furnace to make the background vacuum lower than 0.1 Pa; introduce CS 2 gas into the above tube furnace to form a reducing protective gas atmosphere to avoid Sr 8 Ti 7 S 21The green embryo is oxidized during the high-temperature sintering process; the gas pressure in the above-mentioned tube furnace is adjusted to 30Pa, the tube furnace is heated to the set sintering temperature of 900℃, and maintained for 1h to complete the high-temperature sintering reaction, and then the tube furnace temperature is lowered to room temperature, the tube furnace is opened, and the thermistor material Sr is taken out. 8 Ti 7 S 21 .

[0053] The above preparation method can prepare negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0054] like Figure 4 As shown, thermistor material Sr 8 Ti 7 S 21 The ln(ρ)~1000 / T shows a good linear relationship, which can realize accurate temperature-resistance sensing function. Its room temperature resistance is 7.3Ω·cm.

[0055] Example 4

[0056] Step S1, Sr 8 Ti 7 S 21 Powder preparation: weigh a certain amount of SrTiO 3 Raw material powder, SrTiO 3 The raw material powder was placed in a quartz boat and the SrTiO 3 The quartz boat of raw material powder is placed in a tube furnace. To avoid the influence of other impurities in the air, the tube furnace is evacuated to make the background vacuum lower than 0.1Pa. The sulfiding gas is introduced into the tube furnace. The sulfiding gas here is CS 2 ; Adjust the gas pressure in the above tube furnace to 30Pa, heat the tube furnace to 1000℃, maintain for 1h, complete the sulfurization reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, take out the powder, which is Sr 8 Ti 7 S 21 Powder.

[0057] Step S2, Sr 8 Ti 7 S 21 Preparation of embryo: weigh a certain amount of Sr 8 Ti 7 S 21The powder is placed into a graphite mold; the above graphite mold is placed into a tablet press, and pressure is applied to the mold to make the pressure reach 50 MPa; a high-frequency hot press is used to rapidly heat up the graphite mold to 400 °C, keep it warm for 2 min, then cool it down to room temperature, and demold the graphite mold, thus obtaining the Sr 8 Ti 7 S 21 green body;

[0058] Step S3, preparation of the thermistor Sr 8 Ti 7 S 21 Preparation: The Sr 8 Ti 7 S 21 green body obtained in Step S2 is placed into a tube furnace; to avoid the influence of other impurities in the air, the tube furnace is evacuated to make the background vacuum lower than 0.1 Pa; CS 2 gas is introduced into the above tube furnace to form a reducing protective gas atmosphere to avoid the Sr 8 Ti 7 S 21 green body from being oxidized during the high-temperature sintering process; the air pressure inside the above tube furnace is adjusted to 30 Pa, the tube furnace is heated up to the set sintering temperature of 800 °C, kept for 1 h to complete the high-temperature sintering reaction, then the temperature of the tube furnace is lowered to room temperature, the tube furnace is opened, and the thermistor material Sr 8 Ti 7 S 21 is taken out.

[0059] The above preparation method can prepare the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0060] As Figure 5 shown, for the thermistor material Sr 8 Ti 7 S 21 , the ln(ρ) ~ 1000 / T shows a good linear relationship and can achieve an accurate temperature-resistance sensing function. Its room temperature resistance is 15.9 Ω·cm.

[0061] Example 5

[0062] Step S1, preparation of the Sr 8 Ti 7 S 21 powder: Weigh a certain amount of SrTiO 3 raw material powder, place the SrTiO 3 raw material powder into a quartz boat, and the quartz boat carrying the SrTiO 3The quartz boat containing the raw material powder is placed in a tube furnace; to avoid the influence of other impurities in the air, the tube furnace is evacuated to make the background vacuum lower than 0.1 Pa; a sulfide gas is introduced into the above tube furnace, and the sulfide gas here is H 2 S; adjust the air pressure in the above tube furnace to 30 Pa, heat the tube furnace to 1000 °C, hold for 1 h to complete the sulfidation reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the powder, which is Sr 8 Ti 7 S 21 powder.

[0063] Step S2, Sr 8 Ti 7 S 21 Green body preparation: Weigh a certain amount of Sr 8 Ti 7 S 21 powder, and put it into a graphite mold; put the above graphite mold into a tablet press, apply pressure to the mold to make the pressure reach 50 MPa; use a high-frequency hot press to quickly heat the graphite mold to 400 °C, hold for 2 min, then cool to room temperature, and demold the graphite mold to obtain Sr 8 Ti 7 S 21 green body;

[0064] Step S3, preparation of the thermistor Sr 8 Ti 7 S 21 Prepare: Put the Sr 8 Ti 7 S 21 green body obtained in step S2 into a tube furnace; to avoid the influence of other impurities in the air, the tube furnace is evacuated to make the background vacuum lower than 0.1 Pa; introduce CS 2 gas into the above tube furnace to form a reducing protective gas atmosphere to avoid Sr 8 Ti 7 S 21 green body from oxidizing during high-temperature sintering; adjust the air pressure in the above tube furnace to 30 Pa, heat the tube furnace to the set sintering temperature of 1100 °C, hold for 1 h to complete the high-temperature sintering reaction, then lower the temperature of the tube furnace to room temperature, open the tube furnace, and take out the thermistor Sr 8 Ti 7 S 21 .

[0065] The above preparation method can prepare the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

[0066] As Figure 6 shown, for the thermistor material Sr 8 Ti 7 S 21 the ln(ρ)~1000 / T shows a good linear relationship and can achieve an accurate temperature-resistance sensing function. Its room temperature resistance is 0.7 Ω·cm.

[0067] In summary, any one of the negative temperature coefficient thermistor materials obtained in Examples 1-5 shows good resistance-temperature correlation performance and can achieve an accurate temperature-resistance sensing function, proving the rationality of the technical solution of the present invention.

[0068] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. Preparation method of a negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 ​ It is characterized in that It includes the following steps: Step S1, using SrTiO 3 as the raw material, carry out a sulfidation reaction to obtain Sr 8 Ti 7 S 21 powder; In the vulcanization reaction of step S1, it is carried out in a tubular furnace. After evacuating the tubular furnace, a vulcanizing gas is introduced, the air pressure in the furnace is adjusted, and after heating to the reaction temperature, the vulcanization reaction is carried out; The sulfurized gas is CS 2 or H 2 S; The described tubular furnace is evacuated before the reaction to make the background vacuum as low as 0.1 Pa. After introducing the sulfiding gas, the pressure inside the furnace is 30 Pa, and the reaction temperature is 1000 °C. The sulfiding reaction is carried out to obtain Sr 8 Ti 7 S 21 powder Step S2, subject the Sr 8 Ti 7 S 21 powder obtained in Step S1 to hot pressing to obtain a green body of Sr 8 Ti 7 S 21 ; Step S3: subject the Sr 8 Ti 7 S 21 green compact to high-temperature sintering to obtain a negative temperature coefficient thermistor Sr 8 Ti 7 S 21 ; In the high-temperature sintering process in step S3, the Sr obtained in step S2 8 Ti 7 S 21 green compact is placed in a tube furnace. The tube furnace is evacuated before the reaction to make the background vacuum as low as 0.1 Pa, and CS 2 gas is introduced for protection. The pressure in the furnace is adjusted to 30 Pa, and the temperature is raised to the sintering temperature of 800 - 1100 °C and kept for 1 h for high-temperature sintering to obtain the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 .

2. The preparation method of the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 as claimed in claim 1 It is characterized in that In the hot pressing process of step S2, it is carried out in a high-frequency hot press. First, a certain pressure is applied, then the temperature is gradually increased, and heat preservation is carried out. After heat preservation for a certain period of time, it is cooled to room temperature to obtain Sr 8 Ti 7 S 21 green compact.

3. The preparation method of the negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 as claimed in claim 2 It is characterized in that In the hot pressing process of step S2, the applied pressure is 50 MPa, the temperature is raised to 400 °C, and the heat preservation time is 2 min.

4. A negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 , It is characterized in that The negative temperature coefficient thermistor material Sr 8 Ti 7 S 21 is prepared by using the preparation method described in any one of claims 1-3 above.

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