CN111490148B - Preparation method of polycrystalline SnSe-based thermoelectric material - Google Patents

Preparation method of polycrystalline SnSe-based thermoelectric material Download PDF

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CN111490148B
CN111490148B CN201910077113.4A CN201910077113A CN111490148B CN 111490148 B CN111490148 B CN 111490148B CN 201910077113 A CN201910077113 A CN 201910077113A CN 111490148 B CN111490148 B CN 111490148B
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snse
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thermoelectric material
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CN111490148A (en
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张家华
徐静涛
蒋俊
乐松
江浩川
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Ningbo Institute of Material Technology and Engineering of CAS
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    • H10N10/851—Thermoelectric active materials comprising inorganic compositions
    • H10N10/852—Thermoelectric active materials comprising inorganic compositions comprising tellurium, selenium or sulfur
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Abstract

The invention provides a preparation method of a polycrystalline SnSe-based thermoelectric material. The method comprises the steps of preparing SnSe-based polycrystalline ingots through smelting, adding one or more of Te, Se, Pb, Br, Sn, Sb and Bi as sintering aids in the ingot ball milling process to obtain powder, and sintering the powder into blocks through hot pressing. The method can promote the recrystallization and the directional rearrangement of the crystal grains, improve the orientation degree of the crystal grains and optimize the texture degree of the SnSe-based thermoelectric material, thereby improving the thermoelectric property of the SnSe-based thermoelectric material and having good application prospect.

Description

Preparation method of polycrystalline SnSe-based thermoelectric material
Technical Field
The invention belongs to the technical field of thermoelectric materials, and relates to a preparation method of a polycrystalline SnSe-based thermoelectric material.
Background
The thermoelectric material directly realizes the mutual conversion of electric energy and heat energy by utilizing the transport energy of phonons and carriers. Over the past several years, Thermoelectric (TE) materials have attracted continuous attention from countries around the world as a new green, energy-saving and environmentally friendly material. The thermoelectric equipment has the advantages of small volume, no noise, no external transmission device, low cost, energy conservation, environmental protection and the like, so that the thermoelectric equipment has related application in the market gradually at present and has wide future prospect.
The performance of thermoelectric materials is defined by a dimensionless thermoelectric figure of merit (ZT value): ZT ═ S 2 σ T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the temperature. The wide application of current thermoelectric technology is limited by the low conversion efficiency of thermoelectric materials. The thermoelectric figure of merit and conversion efficiency are directly related, and to achieve high thermoelectric figure of merit, two strategies are possible: 1. high power factor (S) 2 σ), 2, low thermal conductivity (κ). Wherein the doping of resonant state energy level and the carrier concentration regulation are adoptedThe band gap can effectively improve S by means of shrinkage and the like 2 A value of σ; and methods to reduce thermal conductance include layered architecture, nano-precipitation, introduction of point defects and dislocations.
SnSe is a high-performance material consisting of a large amount of environmentally friendly materials, which has ultra-low thermal conductivity and excellent thermoelectric properties. At room temperature a layered structure with a Pnma space group can be observed, which shows a highly symmetrical orthorhombic structure with a Cmcm space group when the temperature exceeds 750K. In recent years, single crystal SnSe was prepared by bridgman method by zhao et al, taking advantage of its ultra-low thermal conductivity and excellent power factor, and its ZT value was reported to exceed 2.0(L.D zhao. et al. science 2016), which is a group of thermoelectric materials having the best performance so far. However, the weak mechanical properties of single crystal SnSe severely restrict the large scale application of thermoelectric devices. Therefore, polycrystalline SnSe thermoelectric materials have attracted research interest to a number of technologists.
At present, some researches have reached the purpose of optimizing electrical properties by adding a dopant to SnSe to regulate the carrier concentration. For example, doping with Ag, Zn, Br, BiCl3, PbBr2, etc. is an effective method in P-type and n-type polycrystalline SnSe. Ningfeng et al prepare Na-doped polycrystalline SnSe by a smelting method combined with hot-pressing sintering, and the carrier concentration reaches about 2.7 multiplied by 10 at room temperature 19 cm -3 ZT is 0.8 at 773K (z.ren et al j. mater.chem.a,2015), but at the same time there is a great room for improvement in ZT values. There have also been studies to optimize the texture of polycrystalline SnSe by changing the synthesis method to improve thermoelectric performance, for example, to adjust the degree of texture of the sample by control of sintering temperature in SPS process to make the average ZT value 0.38(j.he et al phys. In addition, jiang jun et al prepared polycrystalline SnSe by the local melting and SPS methods, because of high texture and hole concentration, ZT values exceeded 1.0(j.jiang et al j.mater.chem.a, 2016).
Disclosure of Invention
In view of the current research situation, the invention provides a preparation method of a polycrystalline SnSe-based thermoelectric material, which is simple and feasible, and can effectively optimize the texture of the polycrystalline SnSe-based thermoelectric material and improve the electrical property of the polycrystalline SnSe-based thermoelectric material, thereby obtaining good thermoelectric property.
The technical scheme of the invention is as follows: a preparation method of a polycrystalline SnSe-based thermoelectric material comprises the following steps:
preparing raw materials according to the stoichiometry of the SnSe-based thermoelectric material;
smelting the raw materials to obtain SnSe-based polycrystalline ingot;
carrying out ball milling on the SnSe-based polycrystal ingot to obtain powder, and then carrying out hot-pressing sintering to obtain a block material;
the method is characterized in that: adding a sintering aid in the ball milling process of the SnSe-based polycrystal ingot casting to perform mixing and ball milling;
the sintering aid is at least one of Te, Se, Pb, Br, Sn, Sb and Bi; and the mass of the sintering aid accounts for 5-50% of that of the SnSe-based polycrystalline ingot.
The chemical structural formula of the SnSe-based thermoelectric material can be M x Sn 1-x Se, wherein M is at least one of Na, Ag, Pb, Cu, Mn, K, Zn, In, Bi, Sb and the like, and x is more than or equal to 0 and less than or equal to 0.5.
As an implementation manner, the smelting process is as follows: and (3) vacuum sealing the raw materials in a quartz tube, placing the quartz tube in a smelting furnace, heating to smelt the raw materials, and naturally cooling the quartz tube to room temperature after smelting is finished to obtain the SnSe-based polycrystalline ingot.
Preferably, the powder has a particle size in the range of 0.5 to 500. mu.m.
Preferably, the raw materials are filled in a quartz tube, and the quartz tube is vacuumized to be less than or equal to 5Pa and then sealed.
Preferably, the smelting furnace is a high-temperature sintering furnace, and the quartz tube swings in the smelting process to uniformly mix the raw materials.
Preferably, the temperature is raised to 850-1000 ℃ in the smelting process.
As one implementation manner, the hot-pressing sintering process is as follows: and putting the powder into a mold, putting the mold into a vacuum hot-pressing furnace, vacuumizing to no more than 10Pa, and carrying out hot pressing. Preferably, the hot-pressing sintering temperature is 350-550 ℃, and the pressure is 50-80 Mpa.
More preferably, the temperature increase rate is controlled to 3 ℃/min to 30 ℃/min.
Further preferably, the pressurizing rate is controlled to be 1MPa/min to 30 MPa/min.
More preferably, the holding time is 10 to 20 min.
More preferably, the pressure release rate after completion of the sintering is 20 MPa/min.
Compared with the prior art, the invention prepares the SnSe-based polycrystalline ingot by a smelting method, as shown in figure 1, adding one or more of Te, Se, Pb, Br, Sn, Sb and Bi as sintering aids in the ingot ball milling process to obtain powder, carrying out hot-pressing sintering on the powder, the sintering aid is melted into liquid in the hot-pressing sintering process to form a liquid-phase sintering mode, and the liquid sintering aid promotes the recrystallization and directional rearrangement of crystal grains in combination with the pressurizing process, the crystal grains form a certain orientation, the texture degree of the SnSe-based thermoelectric material is optimized, the electric transport performance of the SnSe-based thermoelectric material is closer to single crystal, therefore, the thermoelectric property of the SnSe-based thermoelectric material is improved, on the other hand, a large amount of liquid sintering aid is extruded out of the die after pressurization, and a small amount of liquid sintering aid can be filled in gaps among SnSe crystal grains, thereby avoiding the occurrence of oxidation. The method is simple and easy to implement, and is also suitable for other layered thermoelectric materials, the polycrystalline SnSe-based thermoelectric material prepared by the preparation method has high orientation degree and good thermoelectric performance, the crystal orientation degree is more than or equal to 0.4, the thermoelectric figure of merit at 750-800K is more than 0.5, and the application prospect is good.
Drawings
Fig. 1 is a schematic view showing effects of the method for preparing a polycrystalline SnSe-based thermoelectric material according to the present invention.
FIG. 2 is an XRD spectrum of the polycrystalline SnSe-based thermoelectric materials prepared in the embodiments 1-5 of the present invention.
Fig. 3 is a scanning electron microscope photograph of the polycrystalline SnSe-based thermoelectric materials prepared in examples 1, 3 and 5 of the present invention.
FIG. 4 is a Seebeck coefficient versus temperature relationship for polycrystalline SnSe-based thermoelectric materials prepared in examples 1 to 5 of the present invention.
FIG. 5 shows the temperature dependence of the electrical conductivity of the polycrystalline SnSe-based thermoelectric materials prepared in examples 1 to 5 of the present invention.
FIG. 6 is a graph showing the relationship between the thermal conductivity of the polycrystalline SnSe-based thermoelectric materials obtained in examples 1 to 5 of the present invention and the temperature.
FIG. 7 is a graph showing the relationship between thermoelectric figure of merit of the polycrystalline SnSe-based thermoelectric materials obtained in examples 1 to 5 of the present invention and the temperature.
Fig. 8 is a comparison of the average thermoelectric figure of merit of the polycrystalline SnSe-based thermoelectric material prepared in example 5 of the present invention with that of a conventional polycrystalline SnSe-based thermoelectric material.
Detailed Description
The present invention will be described in further detail with reference to the following examples and drawings, which are intended to facilitate the understanding of the present invention and are not intended to limit the present invention in any way.
Example 1:
in this example, polycrystalline Sn 0.97 Na 0.03 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Sn 0.97 Na 0.03 Weighing Sn particles, Se particles and Na particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then carrying out heat preservation melting at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the cast ingot obtained in the step (4) into a ball milling tank for ball milling for 5min to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10pa, heating to 480 ℃, pressurizing to 60Mpa, controlling the heating rate at 15 ℃/min and the pressurizing rate at 20Mpa/min, keeping the temperature and the pressure for 10min, and then releasing the pressure and demolding at 20 Mpa/min.
Example 2:
in this example, polycrystalline Sn 0.97 Na 0.03 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Sn 0.97 Na 0.03 Weighing Sn particles, Se particles and Na particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then carrying out heat preservation melting at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Te obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Te accounts for 5% of that of the ingot, and the ball milling time is 5min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) and (3) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot pressing furnace, vacuumizing to below 10Pa, heating to 480 ℃, pressurizing to 60Mpa, controlling the heating rate at 15 ℃/min and the pressurizing rate at 20Mpa/min, preserving heat and pressure for 10min, and then releasing pressure and demolding at 20 Mpa/min.
Example 3:
in this example, polycrystalline Sn 0.97 Na 0.03 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Sn 0.97 Na 0.03 Weighing Sn particles, Se particles and Na particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction container in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Te obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Te accounts for 15% of that of the ingot, and the ball milling time is 5min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10Pa, heating to 480 ℃ and pressurizing to 60Mpa, wherein the heating rate is controlled at 15 ℃/min, the pressurizing rate is controlled at 20Mpa/min, keeping the temperature and the pressure for 10min, and then releasing the pressure and demolding at 20 Mpa/min.
Example 4:
in this example, polycrystalline Sn 0.97 Na 0.03 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Sn 0.97 Na 0.03 Weighing Sn particles, Se particles and Na particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction container in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Te obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Te accounts for 25% of that of the ingot, and the ball milling time is 5min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10Pa, heating to 480 ℃ and pressurizing to 60Mpa, wherein the heating rate is controlled at 15 ℃/min, the pressurizing rate is controlled at 20Mpa/min, keeping the temperature and the pressure for 10min, and then releasing the pressure and demolding at 20 Mpa/min.
Example 5:
in this example, polycrystalline Sn 0.97 Na 0.03 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Sn 0.97 Na 0.03 Weighing Sn particles, Se particles and Na particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction container in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then preserving the heat at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Te obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Te accounts for 35% of that of the ingot, and the ball milling time is 5min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10Pa, heating to 480 ℃ and pressurizing to 60Mpa, wherein the heating rate is controlled at 15 ℃/min, the pressurizing rate is controlled at 20Mpa/min, keeping the temperature and the pressure for 10min, and then releasing the pressure and demolding at 20 Mpa/min.
The bulk samples obtained in examples 1 to 5 were subjected to XRD (X-ray Diffraction) test and thermoelectric property test, respectively, in the direction perpendicular to the pressure direction.
FIG. 2 is an XRD spectrum of examples 1 to 5, and the XRD spectrum is used to calculate the orientation factor, which increases with the increase of the content of Te added, so that the orientation of the sample is optimized. In example 5, the sample orientation factor can be up to 0.56.
It can be seen from the SEM images of the blocks obtained in examples 1, 3 and 5 that the blocks obtained in examples 2 to 5 have a gradually larger crystal grain size and a gradually strengthened sample orientation compared to example 1, for example, the SEM images of the blocks obtained in examples 1, 3 and 5 shown in fig. 3 have a structure in which, during sintering, Te melting is extruded to form liquid phase sintering, so that the sample orientation is greatly optimized, and as the Te content increases, the crystal grain size increases and the sample orientation is strengthened. In addition, if liquid Te is filled in the gaps of SnSe grains, the generation of oxidation is also avoided.
FIGS. 4 to 7 are graphs showing the thermoelectric properties of the polycrystalline SnSe matrix obtained in examples 1 to 5 as a function of temperature. The conductivity change trend of the polycrystalline SnSe researched by the inventor is closer to that of single crystal SnSe. As can be seen from fig. 5, the conductivity of the polycrystalline SnSe-based bulk materials obtained in examples 2, 3, 4, and 5 was improved as compared with that of example 1, and particularly, the conductivity of the polycrystalline SnSe-based bulk materials obtained in examples 3, 4, and 5 was significantly improved, and the maximum value thereof reached 167Scm at 353K -1 The value of the polycrystalline SnSe is about 4 times higher than that of other polycrystalline SnSe in a room temperature area. Further, the polycrystalline SnSe substrates obtained in examples 3, 4 and 5 had a maximum value of 98Scm in terms of conductivity at 827K -1 And at this time the maximum value of the power factor thereof was 6.9. mu. Wcm -1 K -2 . As can be seen from the relationship between the thermal conductivity and thermoelectric figure of merit of the polycrystalline SnSe-based bulk materials obtained in examples 1 to 5 shown in FIGS. 6 and 7, the thermoelectric figure of merit of the polycrystalline SnSe-based bulk materials obtained in examples 2 to 5 is greater than 0.5 at 750K to 800K, and the thermoelectric figure of merit of the polycrystalline SnSe-based bulk material obtained in example 2 is greater than or equal to 0.8 at 826K, respectively, due to the low thermal conductivity and the higher power factor, andthe block of example 1 is improved by nearly 60% compared to the block under the same temperature conditions.
Fig. 8 is a graph comparing the average ZT values of the polycrystalline SnSe base blocks obtained in example 5 above, and values reported in association with others. As can be seen from fig. 8, the average thermoelectric figure of merit of the polycrystalline SnSe bulk material prepared in example 5 can be 0.45, which is higher than that of the conventional polycrystalline SnSe bulk material.
Example 6:
in this example, polycrystalline Sn 0.97 Na 0.03 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Sn 0.97 Na 0.03 Weighing Sn particles, Se particles and Na particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 900 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 900 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Se obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Se accounts for 5% of that of the ingot, and the ball milling time is 5min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10Pa, heating to 350 ℃, pressurizing to 60Mpa, controlling the heating rate at 3 ℃/min and the pressurizing rate at 30Mpa/min, keeping the temperature and the pressure for 20min, and then releasing the pressure and demolding at 20 Mpa/min.
Tests show that the highest thermoelectric figure of merit of the prepared polycrystalline SnSe-based thermoelectric material at 750-800K in the direction perpendicular to the pressure direction reaches 0.6.
Example 7:
in this embodiment, the preparation method of the polycrystalline SnSe thermoelectric material is as follows:
(1) weighing Sn particles and Se particles according to the stoichiometric ratio of SnSe as reaction raw materials;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot obtained in the step (4) and Pb into a ball milling tank for ball milling, wherein the mass of the Pb accounts for 15% of that of the ingot, and the ball milling time is 5min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) and (3) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot pressing furnace, vacuumizing to below 10Pa, heating to 400 ℃, pressurizing to 60Mpa, controlling the heating rate at 3 ℃/min and the pressurizing rate at 1Mpa/min, preserving heat and pressure for 10min, and then releasing pressure and demolding at 20 Mpa/min.
Tests show that the highest thermoelectric figure of merit of the prepared polycrystalline SnSe-based thermoelectric material at 750-800K in the direction perpendicular to the pressure direction reaches 0.95.
Example 8:
in this example, poly-Sb 0.05 Ag 0.05 Sn 0.9 Se 0.8 Te 0.2 The preparation method of the thermoelectric material comprises the following steps:
(1) according to Sb 0.05 Ag 0.05 Sn 0.9 Se 0.8 Te 0.2 Weighing Sn particles, Se particles, Ag particles, Sb particles and Te particles as reaction raw materials according to the stoichiometric ratio;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 920 ℃ at the speed of 15 ℃/min, then preserving heat at 920 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Te obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Te accounts for 15% of that of the ingot, and the ball milling time is 10min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10Pa, heating to 500 ℃ and pressurizing to 60Mpa, wherein the heating rate is controlled at 20 ℃/min, the pressurizing rate is controlled at 15Mpa/min, keeping the temperature and the pressure for 10min, and then releasing the pressure and demolding at the pressure of 20 Mpa/min.
Tests show that the highest thermoelectric figure of merit of the prepared polycrystalline SnSe-based thermoelectric material at 750K-800K in the direction perpendicular to the pressure direction reaches 1.05.
Example 9:
in this example, polycrystalline Ag 0.03 Sn 0.97 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Ag 0.03 Sn 0.97 Weighing Sn particles, Se particles and Ag particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 1000 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 1000 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Te obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Te accounts for 50% of that of the ingot, and the ball milling time is 10min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot-pressing furnace, vacuumizing to below 10Pa, heating to 550 ℃, pressurizing to 60Mpa, controlling the heating rate at 15 ℃/min and the pressurizing rate at 20Mpa/min, keeping the temperature and the pressure for 10min, and then releasing the pressure and demolding at 20 Mpa/min.
Tests show that the highest thermoelectric figure of merit of the prepared polycrystalline SnSe-based thermoelectric material at 750K-800K in the direction perpendicular to the pressure direction reaches 0.84.
Example 10:
in this example, polycrystalline Pb 0.04 Sn 0.96 Se 0.7 Br 0.3 The preparation method of the thermoelectric material comprises the following steps:
(1) according to Pb 0.04 Sn 0.96 Se 0.7 Br 0.3 Weighing Sn particles, Se particles, Pb particles and SnBr according to the stoichiometric ratio 2 As a reaction raw material;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to be below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 950 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 950 ℃ for 30min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot obtained in the step (4) and Pb into a ball milling tank for ball milling, wherein the mass of the Pb accounts for 35% of that of the ingot, and the ball milling time is 10min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) and (3) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot pressing furnace, vacuumizing to below 10Pa, heating to 450 ℃, pressurizing to 60Mpa, controlling the heating rate at 30 ℃/min and the pressurizing rate at 30Mpa/min, preserving heat and pressure for 10min, and then releasing pressure and demolding at 20 Mpa/min.
Tests show that the highest thermoelectric figure of merit of the prepared polycrystalline SnSe-based thermoelectric material at 750K-800K in the direction perpendicular to the pressure direction reaches 1.01.
Example 11:
in this example, the polycrystal Bi 0.05 Sn 0.95 The preparation method of the Se thermoelectric material comprises the following steps:
(1) according to Bi 0.05 Sn 0.95 Weighing Sn particles, Se particles and Bi particles as reaction raw materials according to the stoichiometric ratio of Se;
(2) putting the reaction raw materials weighed in the step (1) into a clean and dry reaction container, vacuumizing the reaction container to below 10Pa, and sealing an opening of the reaction container by using oxyacetylene flame;
(3) placing the sealed reaction vessel in a high-temperature sintering furnace, heating to 850 ℃ at the speed of 15 ℃/min, then carrying out heat preservation smelting at 850 ℃ for 60min, and then swinging for 30min at the frequency of 5r/min and the swinging angle of 60 degrees;
(4) after the smelting is finished, closing a power supply of the high-temperature sintering furnace, taking out the reaction container, and cooling the reaction container to room temperature in the air to obtain an SnSe-based thermoelectric material ingot;
(5) putting the ingot and Bi obtained in the step (4) into a ball milling tank for ball milling, wherein the mass of Bi accounts for 40% of that of the ingot, and the ball milling time is 10min, so as to obtain powder with the particle size range of 0.5-500 mu m;
(6) and (3) putting the powder obtained in the step (5) into a graphite mold with the diameter of 12.7mm, putting the mold into a hot pressing furnace, vacuumizing to below 10Pa, heating to 350 ℃, pressurizing to 60Mpa, controlling the heating rate at 15 ℃/min and the pressurizing rate at 20Mpa/min, preserving heat and pressure for 10min, and then releasing pressure and demolding at 20 Mpa/min.
Tests show that the highest thermoelectric figure of merit of the prepared polycrystalline SnSe-based thermoelectric material at 750K-800K in the direction perpendicular to the pressure direction reaches 1.05.
The embodiments described above are intended to illustrate the technical solutions of the present invention in detail, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modification, supplement or similar substitution made within the scope of the principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A method for preparing a polycrystalline SnSe-based thermoelectric material with high degree of orientation and good thermoelectric properties, comprising the steps of:
preparing raw materials according to the stoichiometry of the SnSe-based thermoelectric material;
smelting the raw materials to obtain SnSe-based polycrystalline ingot;
carrying out ball milling on the SnSe-based polycrystalline ingot to obtain powder, and then carrying out hot-pressing sintering to obtain a block material;
the method is characterized in that: adding a sintering aid in the SnSe-based polycrystalline ingot ball milling process to perform mixed ball milling;
the sintering aid is at least one of Te, Se, Pb, Br, Sn, Sb and Bi; moreover, the mass of the sintering aid accounts for 5-50% of that of the SnSe-based polycrystalline ingot;
in the hot-pressing sintering process, the heating rate is 3 ℃/min to 30 ℃/min, and the pressurizing rate is 1Mpa/min to 30 Mpa/min;
the grain orientation degree of the prepared polycrystalline SnSe-based thermoelectric material is greater than or equal to 0.4, and the thermoelectric figure of merit of 750K-800K is higher than 0.5.
2. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the chemical structural formula of the SnSe-based thermoelectric material is M x Sn 1-x Se, wherein M is at least one of Na, Ag, Pb, Cu, Mn, K, Zn, In, Bi and Sb, and x is more than or equal to 0 and less than or equal to 0.5.
3. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the particle size range of the powder is 0.5-500 mu m.
4. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the smelting process comprises the following steps: and (3) vacuum sealing the raw materials in a quartz tube, placing the quartz tube in a smelting furnace, heating to smelt the raw materials, and naturally cooling the quartz tube to room temperature after smelting is finished to obtain the SnSe-based polycrystalline ingot.
5. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the raw materials are put into a quartz tube, and the quartz tube is vacuumized until the pressure is less than or equal to 5Pa and then sealed.
6. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the smelting furnace is a high-temperature sintering furnace, and the quartz tube swings in the smelting process to uniformly mix the raw materials.
7. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: during the smelting process, the temperature is raised to 850-1000 ℃.
8. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the hot pressing process comprises the following steps: and putting the powder into a mold, putting the mold into a vacuum hot-pressing sintering furnace, vacuumizing until the pressure is not higher than 10Pa, and carrying out hot pressing.
9. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: the hot-pressing sintering temperature is 350-550 ℃, and the pressure is 50-80 Mpa.
10. The method of making a polycrystalline SnSe-based thermoelectric material of claim 1, wherein: and in the hot-pressing sintering process, the heat preservation and pressure maintaining time is 10-20 min.
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