A large-size CoSbS-based thermoelectric semiconductor crystal and its preparation method

Abstract

The present invention relates to the technical field of thermoelectric semiconductor materials and discloses a method for preparing large-sized CoSbS-based thermoelectric semiconductor crystals. The large-sized CoSbS-based thermoelectric semiconductor crystals are produced by a vertical drop melt growth method using a CoSbS polycrystalline raw material. The CoSbS polycrystalline raw material is produced by swing melting elemental Co particles, elemental Sb particles, and elemental S particles at 650-750°C. During the swing melting, the elemental S particles are placed below the elemental Co particles and elemental Sb particles. The thermoelectric semiconductor crystals have excellent electrical conductivity. In addition, the thermoelectric semiconductor crystals produced by this method are large in size, simple in process, and can significantly reduce the loss rate of sulfur in the CoSbS polycrystalline raw material.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric semiconductor materials, and in particular to a large-sized CoSbS-based thermoelectric semiconductor crystal and a preparation method thereof. Background Art

[0002] Traditional thermoelectric semiconductor materials are mainly Bi2Te3-based thermoelectric materials and PbTe-based thermoelectric materials. However, the constituent elements of the above two materials are scarce in the earth's crust and the raw materials and products are toxic. Therefore, it is of great significance to find an environmentally friendly, low-toxic thermoelectric semiconductor material with a wide range of raw materials.

[0003] The energy conversion efficiency of thermoelectric conversion technology is measured by the thermoelectric performance of the material. People usually use the thermoelectric figure of merit ZT to characterize the level of thermoelectric performance. The ZT value of thermoelectric materials can be expressed as ZT = S 2 σT / κ, where S is the material's Seebeck coefficient, σ is the material's electrical conductivity, T is the absolute temperature, and κ is the material's total thermal conductivity. CoSbS has a high power factor and good mechanical stability. Electronic structure calculations show that CoSbS's high power factor stems from its multi-valley band dispersion at the top of the valence band and the bottom of the conduction band. Doping can effectively increase the carrier concentration, effective mass of state density, and mobility of CoSbS-based materials. Furthermore, the structure of CoSbS-based materials is a mineral resource with abundant reserves, widespread sources, and environmental friendliness. Therefore, CoSbS-based materials are highly promising thermoelectric semiconductor materials in the medium- and high-temperature range.

[0004] At present, the traditional CoSbS is made by the pressure sintering method (SPS sintering method), such as the preparation method of cubic structure CoSbS thermoelectric compound disclosed in CN109626446B, which presses Co, Sb, and S powders into blocks and then sinters them at high temperature to make CoSbS thermoelectric compound. For example, the reference "SS Zhang, Enhanced thermoelectric performance of CoSbS 0.85 Se 0.15 The CoSbS thermoelectric compound disclosed in the "SPS sintering method" was prepared using a point defect, Rare met. 37 (2017) 326-332. The present inventors discovered that when using the SPS sintering method to prepare CoSbS-based thermoelectric semiconductors, the S element in the pressed raw materials was vaporized after sintering at a temperature of 950-1150°C, resulting in a significant increase in the loss of sulfur. This resulted in the performance of the resulting CoSbS-based thermoelectric semiconductor material failing to meet practical requirements. Summary of the Invention

[0005] To overcome the problem of high sulfur loss rate in the prior art when using the SPS sintering method to prepare CoSbS-based thermoelectric semiconductor crystals, the present invention provides a large-sized CoSbS-based thermoelectric semiconductor crystal and a preparation method thereof. The present invention significantly reduces the sulfur loss rate of the prepared CoSbS polycrystalline raw material by adjusting the stacking method of elemental S particles and other raw material elemental particles in a crucible and controlling the melting temperature. The present invention also uses a melt growth method to grow the CoSbS polycrystalline raw material into a large-sized CoSbS-based thermoelectric semiconductor crystal. The semiconductor crystal has a similar electrical conductivity to that of a semiconductor crystal prepared by the SPS sintering method.

[0006] The specific technical solutions of the present invention are:

[0007] A large-sized CoSbS-based thermoelectric semiconductor crystal is produced by a melt growth method using a CoSbS polycrystalline raw material. The CoSbS polycrystalline raw material is produced by swing melting elemental Co particles, elemental Sb particles, and elemental S particles at 650-750°C. During the swing melting, the elemental S particles are placed below the elemental Co particles and elemental Sb particles.

[0008] Preferably, the large-sized CoSbS-based thermoelectric semiconductor crystal further includes a doping element, wherein the doping element is one of Cu, Zn, Ni and Se, and the doping content is 0-0.2.

[0009] Preferably, the large-sized CoSbS-based thermoelectric semiconductor crystal has a diameter of 10-40 mm and a length of 5-10 cm.

[0010] The present invention provides a large-sized CoSbS-based thermoelectric semiconductor crystal. The semiconductor crystal has a large size, a simple preparation method, and is easy to industrialize. Compared with semiconductor crystals produced by an SPS sintering method, the semiconductor crystal has higher electrical conductivity and better thermoelectric conversion performance. The large-sized CoSbS-based thermoelectric semiconductor crystal of the present invention uses elemental Co particles, elemental Sb particles, and elemental S particles as raw materials to undergo swing melting to produce CoSbS polycrystalline raw materials, which are then melt-grown using the CoSbS polycrystalline raw materials to produce the large-sized CoSbS-based thermoelectric semiconductor crystal. The present invention significantly reduces the sulfur element loss rate of the CoSbS polycrystalline raw materials by adjusting the stacking method of the elemental S particles and other raw material elemental particles in a crucible and controlling the melting temperature, thereby ensuring that the required large-sized CoSbS-based thermoelectric semiconductor crystal can be produced from the subsequent CoSbS polycrystalline raw materials.

[0011] A method for preparing the above-mentioned large-sized CoSbS-based thermoelectric semiconductor crystal comprises the following steps:

[0012] Step 1: Place elemental S particles at the bottom of the crucible, then stack elemental Co particles and elemental Sb particles on top of the elemental S particles, vacuum seal the crucible, and then perform swing melting to produce CoSbS polycrystalline raw material;

[0013] Step 2: Place the CoSbS polycrystalline raw material in a crucible and vacuum seal it, then place the crucible in a vertical crystal growth device. The vertical crystal growth device consists of a melting zone, a cooling crystallization zone, and an annealing zone from top to bottom. First, place the crucible in the melting zone for melting to form a melt, then place the crucible in the cooling crystallization zone and move it for gradient cooling crystallization. Finally, anneal the crucible to form a large-sized CoSbS-based thermoelectric semiconductor crystal.

[0014] Preferably, the temperature of the swing melting in step 1 is 650-750°C.

[0015] Preferably, the swing time of the swing melting in step 1 is 0.5-3 h, and the swing rate is 10-30 r / min.

[0016] Preferably, the amount of CoSbS polycrystalline raw material used in step 2 is 20-100 g.

[0017] The present invention adopts swing melting, which can make the melt after melting more uniformly mixed and improve the uniformity of the CoSbS polycrystalline raw material.

[0018] Preferably, the conditions of the melting zone in step 2 are: temperature of 950-1050°C, heating rate of 1-2.5°C / min, and residence time of 8-20 h.

[0019] Preferably, the conditions of the gradient cooling crystallization zone in step 2 are: a cooling gradient of 15-25°C / cm, and a crucible moving rate of 0.2-3 mm / h.

[0020] Preferably, in step 2, the bottom of the crucible is conical, and the taper of the cone is 17-44°; the diameter of the crucible is 10-50 mm, and the length of the crucible is 20-40 cm.

[0021] The present invention also provides a method for preparing the above-mentioned large-sized CoSbS-based thermoelectric semiconductor crystal. The method grows crystals from CoSbS polycrystalline raw materials through a melt growth method. The method can produce large-sized CoSbS-based thermoelectric semiconductor crystals. The method is simple to operate and easy to promote industrialization.

[0022] Compared with the prior art, the present invention has the following technical effects:

[0023] (1) The present invention significantly reduces the sulfur element loss rate of the prepared CoSbS polycrystalline raw material by adjusting the stacking method of elemental S particles and other raw material elemental particles in the crucible and controlling the melting temperature;

[0024] (2) The large-sized CoSbS-based thermoelectric semiconductor crystals prepared by the present invention have similar electrical conductivity to the CoSbS-based thermoelectric semiconductor crystals prepared by the SPS sintering method;

[0025] (3) The large-sized CoSbS-based thermoelectric semiconductor crystals prepared by the present invention are large in size, simple in preparation method, and easy to be industrialized and promoted. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the X-ray diffraction pattern of the CoSbS-based thermoelectric semiconductor crystal of Example 1.

[0027] Figure 2 Surface morphology and mapping of the CoSbS-based thermoelectric semiconductor crystal of Example 1.

[0028] Figure 3 CoSbS of Example 2 and Comparative Example 1 0.85 Se 0.15 Schematic diagram of the relationship between the thermal conductivity of thermoelectric semiconductor crystals and temperature. Example 2 is in the vertical axis direction, and Comparative Example 1 is prepared by SPS sintering method (reference). DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the embodiments.

[0030] Example 1:

[0031] A method for preparing a large-sized CoSbS-based thermoelectric semiconductor crystal comprises the following steps:

[0032] Step 1: Weigh elemental Co particles, elemental Sb particles, and elemental S particles in a molar ratio of 1:1:1, place the elemental S particles at the bottom of a quartz crucible, then stack the elemental Sb particles and elemental Co particles on the elemental S particles in sequence and vacuum seal them. Place the sealed quartz crucible vertically in a rocking furnace, raise the temperature to 650°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 15 r / min for 1 hour to ensure that the raw materials are fully mixed and react completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0033] Step 2: Take 20 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 10 mm, a length of 20 cm, a conical bottom, and a taper of 35°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 950 °C, the heating rate was 1 °C / min, and the residence time of the quartz crucible was 8 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the temperature gradient of the gradient cooling zone from top to bottom was 15 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce a large-size CoSbS thermoelectric semiconductor crystal with a diameter of 10 mm and a length of 10 cm.

[0034] Example 2:

[0035] A method for preparing a large-sized CoSbS-based thermoelectric semiconductor crystal comprises the following steps:

[0036] Step 1: Weigh elemental Co particles, elemental Sb particles, elemental S particles, and elemental Se particles in a molar ratio of 1:1:0.85:0.15, place the elemental S particles at the bottom of a quartz crucible, and then stack the elemental Se particles, elemental Sb particles, and elemental Co particles on the elemental S particles in sequence and vacuum seal them. Place the sealed quartz crucible vertically in a rocking furnace, raise the temperature to 650°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 10 r / min for 0.5 hour to ensure that the raw materials are fully mixed and react completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0037] Step 2: Take 20 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 10 mm, a length of 20 cm, a conical bottom, and a taper of 35°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 950 °C, the heating rate was 1 °C / min, and the residence time of the quartz crucible was 8 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the temperature gradient from top to bottom in the gradient cooling zone was 20 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce large-size CoSbS with a diameter of 10 mm and a length of 10 cm. 0.85 Se 0.15Thermoelectric semiconductor crystals.

[0038] Example 3:

[0039] A method for preparing a large-sized CoSbS-based thermoelectric semiconductor crystal comprises the following steps:

[0040] Step 1: Weigh elemental Co particles, elemental Sb particles, elemental S particles, and elemental Se particles in a molar ratio of 1:1:0.85:0.15, place the elemental S particles at the bottom of a quartz crucible, and then stack the elemental Se particles, elemental Sb particles, and elemental Co particles on the elemental S particles in sequence and vacuum seal them. Place the sealed quartz crucible vertically in a rocking furnace, raise the temperature to 700°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 20 r / min for 1 hour to ensure that the raw materials are fully mixed and react completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0041] Step 2: Take 50 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 25 mm, a length of 30 cm, a conical bottom, and a taper of 40°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 °C, the heating rate was 1.5 °C / min, and the residence time of the quartz crucible was 12 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the temperature gradient from top to bottom in the gradient cooling zone was 20 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 0.8 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce large-size CoSbS with a diameter of 25 mm and a length of 8 cm. 0.85 Se 0.15 Thermoelectric semiconductor crystals.

[0042] Example 4:

[0043] A method for preparing a large-sized CoSbS-based thermoelectric semiconductor crystal comprises the following steps:

[0044] Step 1: Weigh elemental Co particles, elemental Sb particles, elemental S particles, and elemental Se particles in a molar ratio of 1:1:0.85:0.15, place the elemental S particles at the bottom of a quartz crucible, and then stack the elemental Se particles, elemental Sb particles, and elemental Co particles on the elemental S particles in sequence and vacuum seal them. Place the sealed quartz crucible vertically in a rocking furnace, raise the temperature to 700°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 30 r / min for 3 hours to ensure that the raw materials are fully mixed and react completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0045] Step 2: Take 100 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (quartz crucible is a double-layer crucible with a diameter of 40 mm, a length of 40 cm, a conical bottom and a taper of 47°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1050 °C, the heating rate was 2.5 °C / min, and the residence time of the quartz crucible was 20 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the temperature gradient from top to bottom in the gradient cooling zone was 25 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 0.2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce large-size CoSbS with a diameter of 40 mm and a length of 5 cm. 0.85 Se 0.15 Thermoelectric semiconductor crystals.

[0046] Comparative Example 1:

[0047] Compared with Example 2, the comparative example 1 adopts the reference: "SS Zhang, Enhanced thermoelectric performance of CoSbS 0.85 Se 0.15 Preparation of CoSbS by SPS sintering method disclosed in the paper by point defect, Rare met. 37(2017) 326-332 0.85 Se 0.15 Thermoelectric semiconductor crystal, prepared CoSbS 0.85 Se 0.15 The thermoelectric semiconductor crystal has a diameter of 3 mm and a length of 10 cm.

[0048] Comparative Example 2:

[0049] Compared with Example 1, the quartz crucible in step 2 of Comparative Example 2 is a single-layer crucible, comprising the following steps:

[0050] Step 1: Weigh elemental Co particles, elemental Sb particles, and elemental S particles in a molar ratio of 1:1:1, stack the elemental S particles, elemental Sb particles, and elemental Co particles in sequence into a quartz crucible and vacuum seal them. Place the sealed quartz crucible vertically into a rocking furnace, raise the temperature to 650°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 15 r / min for 1 hour to ensure that the raw materials are fully mixed and reacted completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0051] Step 2: Take 20 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (the quartz crucible is a single-layer crucible with a diameter of 10 mm, a length of 20 cm, a conical bottom, and a taper of 35°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 950 °C, the heating rate was 1 °C / min, and the residence time of the quartz crucible was 8 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the cooling gradient from top to bottom in the gradient cooling zone was 15 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce large-size CoSbS thermoelectric semiconductor crystals.

[0052] Comparative Example 3:

[0053] Compared with Example 1, the quartz crucible in step 2 of Comparative Example 3 is a flat-bottomed crucible, comprising the following steps:

[0054] Step 1: Weigh elemental Co particles, elemental Sb particles, and elemental S particles in a molar ratio of 1:1:1, stack the elemental S particles, elemental Sb particles, and elemental Co particles in sequence into a quartz crucible and vacuum seal them. Place the sealed quartz crucible vertically into a rocking furnace, raise the temperature to 650°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 15 r / min for 1 hour to ensure that the raw materials are fully mixed and reacted completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0055] Step 2: Take 20 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 10 mm, a length of 20 cm, and a flat bottom crucible), and evacuate to 10-3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 950 °C, the heating rate was 1 °C / min, and the residence time of the quartz crucible was 8 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the temperature gradient of the gradient cooling zone from top to bottom was 15 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce large-size CoSbS thermoelectric semiconductor crystals.

[0056] Comparative Example 4:

[0057] Compared with Example 1, the temperature of the melting zone in step 2 of Comparative Example 4 is too low. The melting zone temperature is 800° C. and includes the following steps:

[0058] Step 1: Weigh elemental Co particles, elemental Sb particles, and elemental S particles in a molar ratio of 1:1:1, stack the elemental S particles, elemental Sb particles, and elemental Co particles in sequence into a quartz crucible and vacuum seal them. Place the sealed quartz crucible vertically into a rocking furnace, raise the temperature to 650°C and keep it warm for 1 hour to completely melt the raw materials, then rock and mix at 15 r / min for 1 hour to ensure that the raw materials are fully mixed and reacted completely. After cooling to room temperature, prepare CoSbS polycrystalline raw materials.

[0059] Step 2: Take 20 g of the above CoSbS polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 10 mm, a length of 20 cm, a conical bottom, and a taper of 35°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 800 °C, the heating rate was 1 °C / min, and the residence time of the quartz crucible was 8 h to ensure that the melt was melted and the solid-liquid interface was stable. The quartz crucible was then moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 °C, and the cooling gradient from top to bottom in the gradient cooling zone was 15 °C / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the annealing zone (annealing zone temperature was 500 °C) for annealing to produce large-size CoSbS thermoelectric semiconductor crystals.

[0060] Comparative Example 5:

[0061] Compared with Example 1, the elemental S particles, elemental Sb particles and elemental Co particles in step 1 of Comparative Example 5 are mixed and then placed in a crucible and vacuum-sealed. The elemental S particles are not placed in the lower layer of the metal particles. The other conditions are the same as in Example 1.

[0062] Comparative Example 6:

[0063] Compared with Example 2, the elemental S particles, elemental Se particles, elemental Sb particles and elemental Co particles in step 1 of Comparative Example 6 are mixed and then placed in a crucible and vacuum sealed. The elemental S particles are not placed on the top layer of the metal particles. The other conditions are the same as those in Example 2.

[0064] Comparative Example 7:

[0065] Compared with Example 1, the swing melting temperature in step 1 of Comparative Example 6 was too low, and the melt swing temperature was 350° C., and the other conditions were the same as those in Example 1.

[0066] Comparative Example 8:

[0067] Compared with Example 1, the swing melting temperature in step 1 of Comparative Example 6 is too high, and the melt swing temperature is 950° C., and the other conditions are the same as those in Example 1.

[0068] Figure 1 The X-ray diffraction pattern of CoSbS thermoelectric semiconductor crystal was obtained in Example 1. Figure 1 It can be seen that the grown CoSbS thermoelectric semiconductor crystal is a single phase.

[0069] Figure 2 CoSbS prepared in Example 2 0.85 Se 0.15 Scanning spectrum of thermoelectric semiconductor crystal, from Figure 2 It can be seen that CoSbS 0.85 Se 0.15 The distribution of various elements in the thermoelectric semiconductor crystal is very uniform.

[0070] Figure 3 CoSbS was prepared for Example 2 and Comparative Example 1. 0.85 Se 0.15 The relationship between the thermal conductivity of thermoelectric semiconductor crystals and temperature changes, from Figure 3 It can be seen that Example 2 has similar thermal conductivity as Comparative Example 1.

[0071] The results of Example 1, Comparative Example 2 and Comparative Example 3 show that the size of the crucible has an important influence on the melt growth of the CoSbS crystal raw material. If a single-layer quartz crucible is used in Comparative Example 2, the melt will break through the quartz crucible during the melt growth stage, the melt will flow out, and solution growth will be impossible. If the bottom of the quartz crucible in Comparative Example 3 is flat, too many crystal nuclei will be generated at the bottom of the flat-bottomed crucible, resulting in crystal growth along multiple crystal nuclei, resulting in complex crystal orientation and low crystal orientation of the finally produced CoSbS thermoelectric semiconductor crystal.

[0072] The results of Example 1 and Comparative Example 4 show that the temperature of the melting zone is too low, resulting in the inability of the CoSbS crystal raw material to melt and subsequent melt growth to proceed.

[0073] The sulfur vaporization loss rate of Example 1, Example 2, Comparative Example 5, Comparative Example 6, Comparative Example 7, and Comparative Example 8 was tested. The testing method was as follows: a crucible containing a CoSbS polycrystalline raw material was broken, the CoSbS polycrystalline raw material was removed, and the crucible fragments were collected. The crucible fragments were heated at 1000° C. in a pure oxygen atmosphere. The generated gas after heating was transferred to nitrogen for cooling. The cooled mixed gas was then charged into a gas chromatograph for quantitative analysis of sulfur. The sulfur vaporization loss rate was calculated as follows: sulfur vaporization loss rate = [1-(total mass of raw material-mass of sulfur attached to the crucible surface) / total mass of raw material] × 100%. The test results are shown in Table 1.

[0074] Table 1 Test results

[0075]

[0076] As shown in Table 1, by analyzing the sulfur loss rates of Example 1, Example 2, Comparative Example 5, Comparative Example 6, Comparative Example 7 and Comparative Example 8, it was found that the method provided by the present invention can reduce the sulfur loss rate of the prepared CoSbS polycrystalline raw material to 0.002~0.003%. By analyzing the results of Example 1, Example 2, Comparative Example 5 and Comparative Example 6, it was found that in Comparative Examples 5 and 6, the sulfur loss rate of the CoSbS polycrystalline raw material prepared by directly mixing the elemental S particles and other elemental particles and then transferring them into a crucible for melting reached 0.011~0.012%, which was significantly higher than that of Example 1 and Example 2. By analyzing the results of Example 1 and Comparative Example 8, it was found that the use of an excessively high melting temperature in Comparative Example 8 would cause the sulfur loss rate of the CoSbS polycrystalline raw material to reach 0.021%, which was significantly higher than that of Example 1.

[0077] After analyzing the above results, the present invention believes that elemental sulfur and other raw material elemental particles react and generate sulfides during the melting process. Since the reaction of sulfur and metal to generate sulfides will release a large amount of heat, when the melting temperature is too high, the reaction heat will be transferred to the internal metal, causing the internal metal to melt rapidly, resulting in the collapse of the metal particle structure, and the raw material melt will quickly mix into one. Since the melting process is relatively fast, it will cause the sulfur and metal to react rapidly and quickly release a large amount of reaction heat. The large amount of reaction heat will cause the sulfur element that has not yet reacted to be vaporized in large quantities, thereby significantly increasing the sulfur element vaporization loss rate.

[0078] The raw material particles of the present invention are placed in a special way in the crucible, and the elemental sulfur particles and other raw material elemental particles are stacked in the crucible in sequence, so that the elemental S particles are located in the lower layer of the other raw material elemental particles. When heated, the elemental sulfur will first begin to melt to form a melt. At this time, the elemental sulfur particles in the upper layer will gradually immerse into the sulfur melt and react with the elemental sulfur to form sulfide and generate reaction heat. The reaction heat melts the other elemental particles and further enables the elemental sulfur and the metal element to fully react to form sulfide, without causing overheating in the melt, thereby avoiding the problem of large-scale sulfur gasification caused by rapid accumulation of reaction heat. appearance; in addition, the use of single-substance particles can create larger gaps between the raw materials. When the single-substance particles are not immersed in the sulfur melt, the gap structure can block the heat transfer between metals, ensuring that the reaction speed will not be too fast, so that the sulfur element can have sufficient time to react with other raw materials, further inhibiting sulfur vaporization; the melting temperature cannot be too high. Too high a temperature will cause the reaction heat and external heat to exceed the melting temperature of other raw materials, resulting in other raw materials also melting and entering the underlying sulfur melt, causing all raw materials to quickly mix into one and cause the reaction heat to accumulate rapidly and cause a large amount of sulfur to vaporize.

[0079] In addition, when analyzing the results of Example 1 and Comparative Example 7, it was found that the polycrystalline material with a melting temperature that was too low could not effectively cause the S element to react with the metal, and the heat released when the sulfide was formed was not enough to melt the metal particles, and it was impossible to produce high-quality CoSbS polycrystalline raw materials.

[0080] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a large-sized CoSbS-based thermoelectric semiconductor crystal, characterized in that: The following steps are involved: Step 1: Place elemental S particles at the bottom of the crucible, then stack elemental Co particles and elemental Sb particles on top of the elemental S particles. Vacuum seal the crucible and perform swing melting to produce CoSbS polycrystalline raw material. The melting temperature of the swing melting is 650-750°C. Step 2: Place the CoSbS polycrystalline raw material in a crucible and vacuum seal it. Place the crucible in a vertical crystal growth device. First, place the crucible in the melting zone to melt it into a melt. Then, place the crucible in the cooling crystallization zone and move it for gradient cooling crystallization. Finally, anneal the crucible to form a large-sized CoSbS-based thermoelectric semiconductor crystal.

2. The preparation method according to claim 1, wherein The large-size CoSbS-based thermoelectric semiconductor crystal further includes a doping element, which is one of Cu, Zn, Ni and Se elements, and the doping content is 0-0.

2.

3. The preparation method according to claim 1, wherein The large-size CoSbS-based thermoelectric semiconductor crystal has a diameter of 10 to 40 mm and a length of 5 to 10 cm.

4. The preparation method according to claim 1, wherein The swing melting time in step 1 is 0.5~3 h, and the speed is 10~30 r / min.

5. The preparation method according to claim 1, wherein The amount of CoSbS polycrystalline raw material used in step 2 is 20~100 g.

6. The preparation method according to claim 1, wherein The conditions of the melting zone in step 2 are: temperature of 950~1050℃, heating rate of 1~2.5℃ / min, and residence time of 8~20h.

7. The preparation method according to claim 1, wherein The conditions of the cooling crystallization zone in step 2 are: a temperature gradient of 15-25 °C / cm and a crucible movement rate of 0.2-3 mm / h.

8. The preparation method according to claim 1, wherein In step 2, the bottom of the crucible is conical, and the taper of the cone is 17-44°.

9. The preparation method according to claim 8, wherein The diameter of the crucible is 10-50 mm, and the length of the crucible is 20-40 cm.

Images