Beta-SrZrS3 thermoelectric conversion block material and preparation method thereof

Abstract

The invention is suitable for the technical field of thermoelectric materials, and provides a preparation method of a beta-SrZrS3 thermoelectric conversion block material, which comprises the following steps: carrying out vulcanization reaction on SrZrO3 powder to obtain beta-SrZrS3 powder; and the beta-SrZrS3 powder is subjected to rapid hot pressing sintering to form a block, and the beta-SrZrS3 thermoelectric conversion block material is obtained. The preparation method provided by the invention has the advantages of low cost, simplicity and rapidness, batch synthesis of the SrZrS3 block material can be realized, the synthesis period is shortened, the prepared beta-SrZrS3 thermoelectric conversion block material is pure in phase, uniform in component distribution and high in density, the used raw material is SrZrO3 powder which is cheap and non-toxic and does not need an inert storage environment, and the preparation method is suitable for industrial production. A vacuum tube furnace and a rapid hot pressing furnace are used, preparation is carried out through vulcanization reaction and hot pressing sintering, and the raw materials, the preparation process and the target product meet the environment-friendly requirement, so that the preparation method provided by the embodiment of the invention can be directly expanded to development of thermoelectric conversion application of perovskite sulfide; and a new way is provided for the development of a novel thermoelectric system.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric materials, and in particular relates to a β-SrZrS3 thermoelectric conversion bulk material and a preparation method thereof. Background Art

[0002] Thermoelectric materials are energy materials that can directly realize the mutual conversion between temperature difference and electrical energy. They have important applications in aerospace exploration, precision refrigeration, and power supply for wearable devices. Sulfide perovskite systems have the advantages of low toxicity, high reserves, stable structure, and adjustable band gap. Their thin film materials have been applied to photoelectric detection and solar cells, but there are few studies on thermoelectric conversion applications. Among them, BaZrS3 has a distorted perovskite structure with a band gap of ~1.8 eV. It has been experimentally confirmed to have the potential for good thermoelectric performance, but its preparation temperature is high (~1500℃), and the bulk material is easy to break, resulting in difficulty in forming, which limits the further development of its thermoelectric conversion application. Therefore, it is necessary to develop sulfide perovskite thermoelectric materials with low price, simple and convenient preparation method, and good forming performance.

[0003] SrZrS3 is a new type of perovskite material. The contents of its constituent elements Sr, Zr, and S in the earth's crust are 370, 165, and 350 ppm, respectively, which are much higher than the common components of thermoelectric and optoelectronic materials such as Ge, Cd, In, Se, and Te (1.4, 0.15, 0.25, 0.05, and 0.001 ppm), and it is environmentally friendly. Unlike BaZrS3, the bonding characteristics of SrZrS3 make it easier to form due to its unique mechanical properties, which is conducive to the preparation of large-sized bulk materials or targets. At the same time, its wider band gap of ~2.3 eV can suppress the bipolar effect that causes the performance of thermoelectric materials to decrease at high temperatures. In addition, SrZrS3 has two crystal structures, α-SrZrS3 and β-SrZrS3, which show different band structures and transport properties, providing more space for physical property regulation. The above factors all indicate the potential of SrZrS3 materials for thermoelectric applications.

[0004] However, the main method for preparing SrZrS3 bulk material at present is to use Sr, Zr, S elements or SrS, Zr, S or SrS, ZrS2 for high-temperature melting for tens of hours or days. This method has problems such as easy oxidation of raw materials, high cost, large melting point difference, easy volatility, etc., and the preparation cycle is long, energy-consuming and time-consuming. In addition, there are two crystal structures of SrZrS3, among which α-SrZrS3 is a needle-like phase connected by ZrS6 octahedra, that is, NH4CdCl3 structure; and β-SrZrS3 is a distorted perovskite structure connected by ZrS6 octahedra, that is, GdFeO3 structure. Therefore, the factor of two-phase competition needs to be considered when preparing SrZrS3. The prior art (journal Physical Review Materials, 2023, 7, 085403.) discloses the bonding characteristics and band structure of β-SrZrS3, and indicates the possibility of its high thermoelectric performance. However, the prior art (journal Nano Letters, 2015, 15, 581-585.) discloses that the α-SrZrS3 phase is more stable under standard conditions, and the experimental conditions need to be controlled to prepare the β-SrZrS3 phase. At present, there is no experimental research on the thermoelectric properties of β-SrZrS3 bulk materials. Therefore, it is urgent to develop a new low-cost, simple, convenient and efficient preparation technology to obtain pure phase and high-density β-SrZrS3 bulk materials, which is of great significance for the research and development of thermoelectric materials. Summary of the invention

[0005] The purpose of the embodiments of the present invention is to provide a method for preparing a β-SrZrS3 thermoelectric conversion bulk material, aiming to solve the problems raised in the above-mentioned background technology.

[0006] The embodiment of the present invention is implemented as follows: a method for preparing a β-SrZrS3 thermoelectric conversion bulk material comprises the following steps: (1) subjecting SrZrO3 powder to a sulfurization reaction to obtain β-SrZrS3 powder; (2) The β-SrZrS3 powder is rapidly hot-pressed and sintered into blocks to obtain the β-SrZrS3 thermoelectric conversion bulk material.

[0007] Preferably, the step of subjecting the SrZrO3 powder to a sulfurization reaction to obtain β-SrZrS3 powder is specifically as follows: (1) Place SrZrO3 powder in a tube furnace and evacuate the furnace; (2) Introducing CS2 gas into the furnace; (3) The tube furnace is heated and kept warm, and then cooled to room temperature to obtain β-SrZrS3 powder.

[0008] Preferably, in step (2), the flow rate of the introduced CS2 gas is 35-60 SCCM.

[0009] Preferably, in step (3), the temperature of the tubular furnace is raised to 1000-1200° C., the internal pressure is 35-80 Pa, and the temperature is kept at this temperature for 1-12 hours.

[0010] Preferably, the step of rapidly hot pressing and sintering the β-SrZrS3 powder into a block to obtain the β-SrZrS3 thermoelectric conversion block material is specifically: (1) The β-SrZrS3 powder is placed in a mold for pre-pressing, and then placed in a rapid hot pressing sintering furnace and vacuumed; (2) The temperature in the furnace was controlled to reach 1300°C and kept at that temperature for 5 min at a pressure of 50 MPa. After cooling to room temperature, a β-SrZrS3 thermoelectric conversion bulk material was obtained.

[0011] Preferably, in step (1), the mold is a graphite mold.

[0012] Another object of an embodiment of the present invention is to provide a β-SrZrS3 thermoelectric conversion bulk material, which is prepared by the above-mentioned preparation method.

[0013] A preparation method of a β-SrZrS3 thermoelectric conversion bulk material provided in an embodiment of the present invention has the advantages of low cost, simplicity and rapidity, can realize the batch synthesis of β-SrZrS3 bulk materials and shorten the synthesis cycle, uses cheap and non-toxic SrZrO3 powder as raw materials, and does not require an inert storage environment. It is prepared by a vacuum tube furnace and a rapid hot pressing furnace through a sulfurization reaction and hot pressing sintering, and because the raw materials, preparation process and target product are basically environmentally friendly, the preparation method provided in an embodiment of the present invention can be directly extended to the development of perovskite sulfide thermoelectric conversion applications, providing a new approach for the development of new thermoelectric systems; The prepared β-SrZrS3 thermoelectric conversion bulk material is pure phase, uniformly distributed in composition, and has high density (up to 100%). According to performance tests, its Seebeck coefficient is −475.5 μVK at 323 K. −1 , thermal conductivity is 2.2 Wm −1 K −1 , has significant thermoelectric effect and low thermal conductivity, indicating that it is a potential thermoelectric material in the medium temperature range. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flowchart of a method for preparing a β-SrZrS3 thermoelectric conversion bulk material provided by an embodiment of the present invention; Figure 2 The XRD pattern of the sample provided in Example 1 of the present invention; Figure 3 The SEM morphology images of the sample provided in Example 1 of the present invention, wherein (a) and (b) are the morphology display results at different magnifications; Figure 4 Element distribution mapping diagram of the sample provided in Example 1 of the present invention; Figure 5 The EDS spectrum of the sample provided in Example 1 of the present invention; Figure 6 The temperature-dependent thermoelectric performance results of the sample provided in Example 1 of the present invention, wherein (a) is the Seebeck coefficient, (b) is the resistivity, (c) is the power factor, and (d) is the thermal conductivity. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0016] A β-SrZrS3 thermoelectric conversion bulk material, the preparation method thereof is as follows Figure 1 As shown, the specific steps include: (1) Place SrZrO3 powder in a tube furnace and use a mechanical pump to evacuate the furnace to <0.1Pa; (2) Introduce CS2 gas at a flow rate of 35-60 SCCM; (3) heating the tube furnace to 1000-1200 °C with an internal pressure of 35-80 Pa, keeping the temperature for 1-12 h, and cooling to room temperature to obtain β-SrZrS3 powder; (4) Pre-press the β-SrZrS3 powder in a graphite mold, then place it in a rapid hot pressing sintering furnace and evacuate the furnace to <0.1Pa; (5) Use infrared temperature measuring equipment to monitor the temperature of the sample chamber and make it reach 1300°C. Keep it at this temperature for 5 min and keep it at a pressure of 50 MPa. After cooling to room temperature, a β-SrZrS3 bulk sample is obtained.

[0017] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0018] Embodiment 1: A β-SrZrS3 thermoelectric conversion bulk material, the preparation method of which comprises the following steps: (1) Spread 325 mesh SrZrO3 powder on the bottom of the crucible, place the crucible in the middle of the tubular reactor, use a mechanical pump to evacuate to <0.1 Pa, introduce CS2 gas from one end of the tubular furnace, control the gas flow rate at 35 SCCM, adjust the valve to keep the gas pressure at 35 Pa, set the heating curve to heat the furnace to 1000℃, and keep it warm for 12 h, then cool the furnace naturally to room temperature to obtain a reddish-brown β-SrZrS3 powder precursor; (2) The β-SrZrS3 powder precursor was evenly ground in a mortar and loaded into a graphite mold. The graphite mold was placed in a rapid sintering furnace and vacuumed before rapid hot pressing sintering (pressure 50 MPa, temperature 1300°C, insulation time 5 min) to obtain a β-SrZrS3 bulk material.

[0019] The β-SrZrS3 bulk material prepared in Example 1 was cut and processed as a sample for performance testing: The density of the sample was measured to be 3.9 gcm −3 , the relative density is close to 100%; The sample was analyzed by X-ray diffractometer and the XRD pattern was obtained as shown in Figure 2 As shown, according to Figure 2 It can be seen that it matches the SrZrS3 standard spectrum PDF#04-007-5510; The samples were analyzed using a scanning electron microscope and the microscopic morphology SEM images were obtained. Figure 3 As shown, according to Figure 3 It can be seen that the sample has a high density; The sample was analyzed using a scanning transmission electron microscope to obtain an element distribution mapping diagram such as Figure 4 As shown, according to Figure 4 It can be seen that the sample elements are evenly distributed; The sample was analyzed using an energy spectrometer to obtain an EDS spectrum such as Figure 5 As shown, according to Figure 5 It can be seen that it displays the spectrum peaks of Sr, Zr, and S elements; The variable temperature thermoelectric performance of the sample was analyzed, and the results were as follows: Figure 6 As shown, according to Figure 6 It can be seen that the Seebeck coefficient of the sample is −475.5 μVK at 323 K. −1 , thermal conductivity is 2.2 Wm −1 K −1 , with significant thermoelectric effect and low thermal conductivity.

[0020] Embodiment 2: A β-SrZrS3 thermoelectric conversion bulk material, the preparation method of which comprises the following steps: (1) Spread 325 mesh SrZrO3 powder on the bottom of the crucible, place the crucible in the middle of the tubular reactor, use a mechanical pump to evacuate to <0.1 Pa, introduce CS2 gas from one end of the tubular furnace, control the gas flow rate at 60 SCCM, adjust the valve to keep the gas pressure at 80 Pa, set the heating curve to heat the furnace to 1200℃, and keep it warm for 1 h, then cool the furnace naturally to room temperature to obtain a reddish-brown SrZrS3 powder precursor; (2) The SrZrS3 powder precursor was evenly ground in a mortar and loaded into a graphite mold. The graphite mold was placed in a rapid sintering furnace and vacuumed before rapid hot pressing sintering (pressure 50 MPa, temperature 1300°C, insulation time 5 min) to obtain β-SrZrS3 bulk material.

[0021] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a β-SrZrS3 thermoelectric conversion bulk material, characterized in that: The following steps are involved: (1) subjecting SrZrO3 powder to a sulfurization reaction to obtain β-SrZrS3 powder; (2) The β-SrZrS3 powder is rapidly hot-pressed and sintered into blocks to obtain the β-SrZrS3 thermoelectric conversion bulk material.

2. The method for preparing the β-SrZrS3 thermoelectric conversion bulk material according to claim 1, characterized in that: The step of subjecting the SrZrO3 powder to a sulfurization reaction to obtain β-SrZrS3 powder is specifically as follows: (1) Place SrZrO3 powder in a tube furnace and evacuate the furnace; (2) Introducing CS2 gas into the furnace; (3) The tube furnace is heated and kept warm, and then cooled to room temperature to obtain β-SrZrS3 powder.

3. The method for preparing the β-SrZrS3 thermoelectric conversion bulk material according to claim 2, characterized in that: In step (2), the flow rate of the CS2 gas introduced is 35-60 SCCM.

4. The method for preparing the β-SrZrS3 thermoelectric conversion bulk material according to claim 2, characterized in that: In step (3), the temperature of the tubular furnace is raised to 1000-1200°C, the internal pressure is 35-80Pa, and the temperature is kept at this temperature for 1-12 hours.

5. The method for preparing the β-SrZrS3 thermoelectric conversion bulk material according to claim 1, characterized in that: The step of rapidly hot pressing and sintering the β-SrZrS3 powder into a block to obtain the β-SrZrS3 thermoelectric conversion block material is specifically: (1) The β-SrZrS3 powder is placed in a mold for pre-pressing, and then placed in a rapid hot pressing sintering furnace and vacuumed; (2) The temperature in the furnace was controlled to reach 1300°C and kept at that temperature for 5 min at a pressure of 50 MPa. After cooling to room temperature, a β-SrZrS3 thermoelectric conversion bulk material was obtained.

6. The method for preparing the β-SrZrS3 thermoelectric conversion bulk material according to claim 5, characterized in that: In step (1), the mold is a graphite mold.

7. A β-SrZrS3 thermoelectric conversion bulk material, characterized in that: The material is prepared by the preparation method according to any one of claims 1 to 6.

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