CN115915895B - Preparation method of thermoelectric refrigeration material based on P-type SnSe crystal - Google Patents
Preparation method of thermoelectric refrigeration material based on P-type SnSe crystal Download PDFInfo
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Abstract
The thermoelectric refrigerating material based on the P-type SnSe crystal is a SnSe material doped with Na and additionally introduced with Cu, and the molar ratio of Sn, se, cu and Na is (1-x): 1: y: x; wherein x is more than or equal to 0.015 and less than or equal to 0.025,0.005, and y is more than or equal to 0.03; solves the difficult problem of preparing a large-volume crystal with a low thermal conductivity system, increases the heat transfer performance inside the crystal, and ensures that the inside of the crystal is more compact; the defect concentration in the crystal is promoted to be reduced by additionally introducing Cu, the carrier mobility is improved, and the conductivity is further improved; the interaction of the material multi-valence band is promoted, and the Seebeck coefficient is improved; the ultra-high power factor and the excellent room temperature performance are realized; so that the power factor PF is more than or equal to 100 mu Wcm ‑1 K ‑2 The ZT value at room temperature is more than or equal to 1.4.
Description
Technical Field
The invention relates to the technical field of thermoelectric materials, in particular to a preparation method of a thermoelectric refrigeration material based on a P-type SnSe crystal.
Background
In the context of economic globalization, industry is extremely important in national economy. In the industrial development process, the massive consumption of fossil energy causes serious environmental problems, and the physical and mental health of human beings is directly affected. Therefore, development of new, environmentally friendly energy replacement materials has been urgent;
the thermoelectric material can realize direct conversion of heat energy and electric energy by utilizing carrier transport in the material so as to realize mutual conversion of energy in two forms of electricity and heat, can realize thermoelectric power generation and electrified refrigeration, and has important application prospect in the fields of clean energy and refrigeration; the thermoelectric refrigeration technology is one of the main applications of the thermoelectric technology, and the thermoelectric device gradually becomes a key technology of a plurality of modern industries by virtue of the characteristics of small volume, light weight, long service life and the like, and can be widely applied to the fields of communication, industry, medical treatment, aerospace and the like;
the conversion efficiency of the thermoelectric material is determined by the performance figure of merit ZT value of the thermoelectric material; in a certain temperature range, the higher the average ZT value is, the more excellent the thermoelectric material performance is, and the higher the conversion efficiency of the thermoelectric device prepared by the material is. Therefore, increasing the ZT value and the average ZT value of thermoelectric materials is a major research direction of researchers in recent years.
In the thermoelectric refrigerating material of the prior art, bi 2 Te 3 Is a thermoelectric material which is relatively mature in research and is the only large-scale commercial application; but Bi is 2 Te 3 The raw materials are expensive, the toxicity is large, and the high-temperature instability exists;
the P-type SnSe monocrystal with the orthogonal lamellar structure has excellent thermoelectric performance, and is environment-friendly, low in toxicity, abundant in reserves, low in price, stable in high-temperature performance and ultra-low in lattice thermal conductivity;
the prior art carries out strategies such as carrier concentration optimization, energy band regulation and control and the like on the P-type SnSe crystal, obtains a ZT value reaching about 0.8 at the vicinity of room temperature, and shows great potential of the SnSe crystal as a thermoelectric refrigerating material;
however, the optimization means for the P-type SnSe crystal in the prior art still cannot reach the replacement of Bi 2 Te 3 Is a target of (2); because of the poor processability and the harsh crystal growth process of the P-type SnSe crystal, the preparation of a large-volume crystal with a low thermal conductivity system is difficult; the high-performance P-type SnSe crystal is difficult to be truly applied to large-scale device production, the defect concentration in the P-type SnSe crystal is still at a higher level by the existing optimization means, the carrier mobility is low, and the conductivity is not high; higher power factors and excellent room temperature performance cannot be achieved; the room temperature ZT value of the P-type SnSe cannot be improved to be more than 1.0 by the optimization means of the prior art;
therefore, the technical staff in the art aims to develop a preparation method of a thermoelectric refrigeration material based on a P-type SnSe crystal, and aims to solve the defect problem in the prior art.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the present invention aims to solve the technical problem that it is difficult to prepare a large-volume crystal with a low thermal conductivity system in the prior art; the high-performance P-type SnSe crystal is difficult to be truly applied to large-scale device production, the defect concentration in the P-type SnSe crystal is still at a higher level by the existing optimization means, the carrier mobility is low, and the conductivity is not high; higher power factors and excellent room temperature performance cannot be achieved; the room temperature ZT value of the P-type SnSe cannot be improved to be more than 1.0 by the optimization means of the prior art.
To achieve the above object, a first aspect of the present invention provides a thermoelectric refrigeration material based on P-type SnSe crystal;
the P-type SnSe crystal thermoelectric refrigerating material is a SnSe material doped with Na and additionally introduced with Cu, and the molar ratio of Sn, se, cu and Na is (1-x): 1: y: x; wherein x is more than or equal to 0.015 and less than or equal to 0.025,0.005, and y is more than or equal to 0.03.
The invention provides a preparation method of a thermoelectric refrigeration material based on a P-type SnSe crystal, which comprises the following steps:
step 1, weighing and mixing Sn, se, cu and Na according to the component proportion of the P-type SnSe crystal thermoelectric refrigeration material to obtain a mixed material;
step 2, carrying out high-temperature fusion synthesis and slow cooling on the mixed material to grow crystals, thereby obtaining the P-type SnSe crystal thermoelectric refrigerating material;
the mixed material of the P-type SnSe crystal is prepared by high-temperature fusion synthesis between an inner quartz tube and an outer quartz tube;
the high-temperature fusion synthesis preparation process is carried out under strict vacuum conditions, and the vacuum degree of the vacuum conditions is less than or equal to 1 multiplied by 10 -4 Pa；
The double-layer quartz tube is characterized in that the inner-layer quartz tube is a conical quartz tube with a sharp bottom, and the height of the inner-layer quartz tube is 11-13 cm; the outer quartz tube is a flat bottom quartz tube, and the height is 16-18 cm;
the outer quartz tube is filled with a mixed material, and the inner quartz tube is placed in the mixed material; the angle range of the bottom cone of the inner quartz tube is 18 degrees or more and theta/2 degrees or less and 20 degrees or less; the wall thickness of the inner quartz tube is not less than 1.5mm;
in the preparation process of the continuous temperature zone directional solidification method, a double-layer quartz tube filled with mixed materials needs to be vertically placed;
the temperature program of the vertical high temperature furnace is as follows: firstly, heating to 1100 ℃ at a speed of 60-80 ℃/h, and preserving heat for 1200-1500 min to perform melt synthesis; then slowly cooling to 700-800 ℃ at a speed of 0.8-1.2 ℃/h for crystal growth; finally, cooling to about 30 ℃ at a speed of 5-10 ℃/h to obtain the required P-type SnSe crystal;
further, the wall thickness of the outer quartz tube is not less than 1.8mm; the diameter difference between the diameter of the inner wall of the outer quartz tube and the diameter of the outer wall of the inner quartz tube is not smaller than 4mm;
further, the outer wall of the inner quartz tube and the inner wall of the outer quartz tube are coated with a carbon layer for protection, and the thickness of the carbon layer is not less than 0.15mm;
by adopting the scheme, the thermoelectric refrigeration material based on the P-type SnSe crystal has the following advantages:
(1) According to the thermoelectric refrigeration material based on the P-type SnSe crystal, the quartz tip tube is placed in the flat bottom quartz tube, so that the heat transfer performance in the crystal is improved, the crystal is more compact, and the problem of preparing a large-volume crystal with a low thermal conductivity system is solved; the high-performance P-type SnSe crystal thermoelectric material prepared by the invention is used as a thermoelectric refrigerating device, so that an excellent refrigerating temperature difference effect is realized; can play an irreplaceable important role in small-volume refrigeration and accurate temperature control scenes;
(2) According to the thermoelectric refrigeration material based on the P-type SnSe crystal, the carrier concentration is optimized by doping Na, the defect concentration in the crystal is promoted to be reduced by additionally introducing Cu, the carrier mobility is improved, and the conductivity is further improved; and the introduction of Cu promotes the interaction of multiple valence bands of the material and improves the Seebeck coefficient. The cooperative optimization of the conductivity and the Seebeck coefficient realizes the ultra-high power factor and excellent room temperature performance; so that the power factor PF of the thermoelectric refrigeration material is more than or equal to 100 mu Wcm at room temperature -1 K -2 The ZT value at room temperature is more than or equal to 1.4; snSe crystals obtained based on the invention and the existing commercial Bi 2 Te 3 The built thermoelectric refrigeration device realizes the refrigeration temperature difference of 61.2K by the thermoelectric refrigeration material;
in conclusion, the thermoelectric refrigeration material based on the P-type SnSe crystal disclosed by the invention solves the problem of low heat preparationThe difficult problem of large-volume crystals of the conductor system increases the heat transfer performance inside the crystals, so that the inside of the crystals is more compact; the defect concentration in the crystal is promoted to be reduced by additionally introducing Cu, the carrier mobility is improved, and the conductivity is further improved; the interaction of the material multi-valence band is promoted, and the Seebeck coefficient is improved; the ultra-high power factor and the excellent room temperature performance are realized; so that the power factor PF is more than or equal to 100 mu Wcm -1 K -2 The ZT value at room temperature is more than or equal to 1.4.
The conception, specific technical scheme, and technical effects produced by the present invention will be further described in conjunction with the specific embodiments below to fully understand the objects, features, and effects of the present invention.
Drawings
FIG. 1 is a schematic diagram of a method for improved crystal growth employed in the present invention, wherein the mixture is synthesized at high temperature in the middle of a double-layered quartz tube;
FIG. 2 is a graph showing the data of the results of the temperature (T/K) variation of thermoelectric figure of merit (ZT) of the P-type SnSe thermoelectric refrigeration crystals prepared in examples 1 to 4 and comparative example 1;
FIG. 3 is a graph showing the data of the Power Factor (PF) versus temperature (T/K) for the P-type SnSe thermoelectric refrigeration crystals prepared in examples 1-4 and comparative example 1;
FIG. 4 is a graph showing the data of the results of the temperature (T/K) variation of thermoelectric figure of merit (ZT) of the P-type SnSe thermoelectric refrigeration crystals prepared in examples 5 to 10;
FIG. 5 is a graph showing the data of the Power Factor (PF) of the P-type SnSe thermoelectric refrigeration crystal according to the temperature (T/K) obtained in examples 5-10;
FIG. 6 shows the measured refrigeration temperature difference (. DELTA.T) of a thermoelectric refrigeration device built based on the obtained SnSe crystal max K) a test result data graph;
fig. 7 is a schematic diagram of a thermoelectric refrigeration device built based on the prepared P-type SnSe thermoelectric refrigeration crystal.
Detailed Description
The following describes a number of preferred embodiments of the present invention to make its technical contents more clear and easy to understand. This invention may be embodied in many different forms of embodiments which are exemplary of the description and the scope of the invention is not limited to only the embodiments set forth herein.
The invention provides a thermoelectric refrigeration material based on a P-type SnSe crystal, which is characterized in that the thermoelectric refrigeration material is a SnSe material doped with Na and additionally introduced with Cu, and the molar ratio of Sn, se, cu and Na is (1-x): 1: y: x; wherein x is more than or equal to 0.015 and less than or equal to 0.025,0.005, and y is more than or equal to 0.03;
the value range of x is more than or equal to 0.015 and less than or equal to 0.025, and preferably more than or equal to 0.018 and less than or equal to 0.022;
the value range of y is more than or equal to 0.005 and less than or equal to 0.03, and preferably more than or equal to 0.01 and less than or equal to 0.02;
the additional introduction of the Cu element can effectively reduce the defect concentration in the SnSe crystal and improve the carrier mobility; in addition, cu can effectively promote interaction of multiple valence bands, and the effective quality of the material is improved; the carrier mobility and the effective quality are synergistically optimized, so that higher power factor and ZT value are realized, and especially the ZT value at room temperature reaches more than 1.4;
specifically, cu enters the SnSe crystal to occupy a large amount of Sn vacancies, inhibit the formation of other point defects in the crystal, and greatly reduce the concentration of the point defects in the crystal; the reduction of the point defect concentration weakens the scattering strength of the carrier and improves the carrier mobility;
in terms of energy band structure optimization, cu can further promote valence band alignment effect of the material in a momentum space and an energy space; as the temperature increases, valence band 1 and valence band 2 merge into one energy band (named valence band 1+2) first; the combination of valence band 1 and valence band 2 reduces the total effective mass from two energy bands to one energy band, which is beneficial to increase carrier mobility and prevent inter-valley scattering; then, with increasing temperature, valence band 3 is aligned with valence band 1+2; this process increases the effective mass, thus achieving a high seebeck coefficient;
the power factor of the thermoelectric refrigeration material is obviously improved by the cooperative optimization of the comprehensive carrier mobility and the Seebeck coefficient;
the invention provides a preparation method of a thermoelectric refrigeration material based on a P-type SnSe crystal, which comprises the following steps:
step 1, weighing and mixing Sn, se, cu and Na according to the component proportion of the P-type SnSe crystal thermoelectric refrigeration material to obtain a mixed material;
step 2, carrying out high-temperature fusion synthesis and slow cooling on the mixed material to grow crystals, thereby obtaining the P-type SnSe crystal thermoelectric refrigerating material;
in the specific implementation of the method, the raw materials of Sn, se, cu and Na are selected to have the purity of more than or equal to 99.99 percent;
in the practice of the process of the present invention, all of the starting components are commercially available products well known to those skilled in the art, unless specified otherwise;
in the implementation of the method of the invention, the weighing and mixing process of the raw materials is preferably carried out under an inert atmosphere, and the method of the invention is not limited in any way to the type of gas in the inert atmosphere, and inert atmospheres well known to those skilled in the art are adopted;
in the implementation of the method, the inert atmosphere can prevent the oxidation of Na element; the mixing mode is not particularly limited, and can be performed by mixing modes well known to those skilled in the art;
in the invention, the mixed material is preferably synthesized in a double-layer quartz tube in a high-temperature fusion way; the inner layer quartz tube adopts a quartz tube with a conical bottom, and the height is preferably about 11-13 cm; the outer quartz tube adopts a quartz tube with a flat bottom at the bottom, and the height is preferably about 16-18 cm;
in the invention, the high-temperature fusion synthesis process carries out crystal growth under strict vacuum condition, and the vacuum condition of the outer quartz tube is preferably that the vacuum degree is less than or equal to 1 multiplied by 10 -4 Pa; in the invention, the vacuum degree condition can prevent the raw materials from being oxidized in the high-temperature growth process of the crystal;
the vacuum and sealing treatment is not limited in any particular way, and the vacuum and sealing treatment is carried out by adopting a sealing process well known to a person skilled in the art; in the specific embodiment of the invention, an oxyhydrogen flame is specifically adopted to seal a quartz tube;
in the invention, the high-temperature synthesis preparation process is carried out in a continuous temperature zone, and the high-temperature synthesis preparation process is a directional solidification method;
in the invention, the outer quartz tube is filled with a mixed material, and the inner quartz tube is placed in the mixed material;
the angle range of the bottom cone of the inner quartz tube is preferably 18 degrees or more and theta/2 degrees or less and 20 degrees or less;
the diameter of the outer quartz tube can be changed according to the requirement of the crystal volume, which is an advantage of the novel crystal growth method;
the pointed cone-shaped bottom of the inner quartz tube is beneficial to the formation of seed crystals of the molten mixed raw materials in the outer quartz tube in the slow cooling process, and along with the progress of the slow cooling process, the crystals grow continuously along the crystal orientation of the seed crystals, so that a crystal sample is finally formed;
in the invention, the wall thickness of the inner quartz tube is preferably not less than 1.5mm, more preferably not less than 1.7mm;
the wall thickness of the outer quartz tube is preferably not less than 1.8mm, more preferably not less than 2.1mm;
the diameter difference between the diameter of the inner wall of the outer quartz tube and the diameter of the outer wall of the inner quartz tube is preferably not less than 4mm, more preferably not less than 7mm;
the wall thickness and diameter conditions of the outer quartz tube can better protect the sample from oxidation in the high-temperature fusion synthesis and crystal growth processes of the sample;
in the invention, the outer wall of the inner quartz tube and the inner wall of the outer quartz tube are coated with a carbon layer for protection, and the thickness of the carbon layer is preferably not less than 0.15mm, more preferably not less than 0.2mm;
in the invention, the carbon layer can effectively avoid the Na element from directly contacting the inner wall of the quartz tube to generate chemical reaction;
in the present invention, the carbon layer is preferably obtained by a high-temperature pyrolytic carbon vapor deposition method; the conditions for the deposition are not particularly limited, and deposition conditions well known to those skilled in the art may be employed;
in the invention, the double-layer quartz tube filled with the mixed material is vertically placed in a continuous temperature zone for directional solidification;
in the invention, the temperature program of the vertical high temperature furnace is as follows: firstly, heating to 1100 ℃ at a speed of 60-80 ℃/h, and preserving heat for 1200-1500 min for fusion synthesis; then slowly cooling to 700-800 ℃ at a speed of 0.8-1.2 ℃/h for crystal growth; finally, cooling to about 30 ℃ at a speed of 5-10 ℃/h; more preferably: firstly, heating to 1100 ℃ at a speed of 65-75 ℃/h, preserving heat for 1300-1400 min for fusion synthesis, then slowly cooling to 720-760 ℃ at a speed of 0.9-1.1 ℃/h for crystal growth, and finally cooling to about 30 ℃ at a speed of 6-8 ℃/h; finally obtaining the required P-type SnSe crystal;
in the invention, the heating and heat preservation process can synthesize the SnSe material in a molten state; the slow cooling process can grow to obtain high-quality SnSe crystals;
the invention also provides the P-type SnSe thermoelectric material or the P-type SnSe crystal thermoelectric refrigerating material prepared by the preparation method, and the power factor PF is more than or equal to 100 mu Wcm -1 K -2 The ZT value at room temperature is more than or equal to 1.4; snSe crystals obtained based on the invention and the existing commercial Bi 2 Te 3 The built thermoelectric refrigeration device realizes the refrigeration temperature difference of 61.2K by the thermoelectric refrigeration material; the material has excellent thermoelectric performance, especially in room temperature and low temperature sections, and has potential as thermoelectric refrigerating material;
the P-type SnSe crystal thermoelectric material is used as a new generation of green and environment-friendly thermoelectric material, and plays an irreplaceable important role in a small-volume refrigeration and accurate temperature control scene;
example 1
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.005:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 16cm, the inner diameter of 25mm, the tube wall thickness of 2.1mm and the outer wall carbon layer thickness of 0.2 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 11cm, the inner diameter of 12mm, the tube wall thickness of 1.7mm and the inner wall carbon layer thickness of 0.2 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 1 multiplied by 10 -4 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 70 ℃/h, and preserving heat for 1400min; then cooling to 750 ℃ at a speed of 1 ℃/h, and cooling to 30 ℃ at a speed of 5 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 2
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.01:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 17cm, the inner diameter of 26mm, the tube wall thickness of 2.2mm and the outer wall carbon layer thickness of 0.21 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 12cm, the inner diameter of 12.5mm, the tube wall thickness of 1.8mm and the inner wall carbon layer thickness of 0.21 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 6 multiplied by 10 - 5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 60 ℃/h, and preserving heat for 1300min; then cooling to 720 ℃ at the speed of 0.8 ℃/h, and cooling to 30 ℃ at the speed of 6 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 3
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.015:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 18cm, the inner diameter of 25mm, the tube wall thickness of 2.3mm and the outer wall carbon layer thickness of 0.22 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 13cm, the inner diameter of 12mm, the tube wall thickness of 1.9mm and the inner wall carbon layer thickness of 0.22 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 8 multiplied by 10 -5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at the speed of 80 ℃/h, and preserving heat for 1500min; then cooling to 760 ℃ at the speed of 1.2 ℃/h, and cooling to 30 ℃ at the speed of 7 ℃/h. Finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 4
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.02:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 17cm, the inner diameter of 25mm, the tube wall thickness of 2.5mm and the outer wall carbon layer thickness of 0.23 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 12cm, the inner diameter of 12.5mm, the tube wall thickness of 2.0mm and the inner wall carbon layer thickness of 0.23 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 1 multiplied by 10 - 4 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at the speed of 80 ℃/h, and preserving heat for 1200min; then cooling to 730 ℃ at the speed of 0.8 ℃/h, and cooling to 30 ℃ at the speed of 8 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 5
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.025:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 16cm, the inner diameter of 26mm, the tube wall thickness of 1.9mm and the outer wall carbon layer thickness of 0.24 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 11cm, the inner diameter of 12.5mm, the tube wall thickness of 1.9mm and the inner wall carbon layer thickness of 0.24 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 8 multiplied by 10 - 5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 60 ℃/h, and preserving heat for 1500min; then cooling to 750 ℃ at the speed of 0.9 ℃/h, and cooling to 30 ℃ at the speed of 9 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 6
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.03:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 17cm, the inner diameter of 25mm, the tube wall thickness of 2.3mm and the outer wall carbon layer thickness of 0.25 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 12cm, the inner diameter of 12.5mm, the tube wall thickness of 1.8mm and the inner wall carbon layer thickness of 0.25 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 5 multiplied by 10 - 5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 70 ℃/h, and preserving heat for 1200min; then cooling to 760 ℃ at the speed of 0.9 ℃/h, and cooling to 30 ℃ at the speed of 10 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 7
Weighing and mixing Sn, se, cu and Na blocks with the purity of more than 99.99% in a glove box of inert gas nitrogen according to the proportion of the mol ratio of Sn, se, cu and Na of 0.985:1:0.005:0.015 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 17cm, the inner diameter of 25mm, the tube wall thickness of 2.2mm and the outer wall carbon layer thickness of 0.25 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 13cm, the inner diameter of 12.5mm, the tube wall thickness of 1.7mm and the inner wall carbon layer thickness of 0.26 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 7 multiplied by 10 - 5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 60 ℃/h, and preserving heat for 1300min; then cooling to 760 ℃ at a speed of 1 ℃/h, and cooling to 30 ℃ at a speed of 9 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 8
Weighing and mixing Sn, se, cu and Na blocks with the purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.975:1:0.005:0.025 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 18cm, the inner diameter of 26mm, the tube wall thickness of 2.3mm and the outer wall carbon layer thickness of 0.25 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 12cm, the inner diameter of 13mm, the tube wall thickness of 1.8mm and the inner wall carbon layer thickness of 0.27 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 8 multiplied by 10 -5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at the speed of 80 ℃/h, and preserving heat for 1400min; then cooling to 750 ℃ at a speed of 1.1 ℃/h, and cooling to 30 ℃ at a speed of 8 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 9
Weighing and mixing Sn, se, cu and Na blocks with the purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.975:1:0.015:0.025 to obtain a mixed material;
the mixed material is put into an outer layer flat bottom quartz tube (the height is 16cm, the inner diameter is 25mm, the tube wall thickness is 2.1mm, the outer wall carbon layer thickness is 0.28 mm), and an inner layer sharp cone bottom quartz tube (the height is 11cm, the inner diameter is 12mm, the tube) is inserted into the mixed materialThe thickness of the wall is 1.9mm, the thickness of the carbon layer of the inner wall is 0.28 mm), and the vacuum is pumped until the vacuum degree is less than 5 multiplied by 10 -5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at the speed of 80 ℃/h, and preserving heat for 1500min; then cooling to 740 ℃ at the speed of 0.9 ℃/h, and cooling to 30 ℃ at the speed of 7 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Example 10
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.981:1:0.015:0.019 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 16cm, the inner diameter of 26mm, the tube wall thickness of 2.4mm and the outer wall carbon layer thickness of 0.28 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 12cm, the inner diameter of 12.5mm, the tube wall thickness of 2.0mm and the inner wall carbon layer thickness of 0.29 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 5 multiplied by 10 - 5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 70 ℃/h, and preserving heat for 1400min; then cooling to 730 ℃ at the speed of 0.9 ℃/h, and cooling to 30 ℃ at the speed of 6 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material;
and cutting and polishing the obtained SnSe crystal into a specific shape, and carrying out subsequent test characterization of thermoelectric performance parameters and assembly test of single-arm and multi-pair thermoelectric refrigerating devices.
Comparative example 1
Weighing and mixing Sn, se, cu and Na blocks with purity of more than 99.99% in a glove box of inert gas nitrogen according to the molar ratio of Sn, se, cu and Na of 0.98:1:0.035:0.02 to obtain a mixed material;
putting the mixed material into an outer layer flat bottom quartz tube (with the height of 16cm, the inner diameter of 25mm, the tube wall thickness of 2.3mm and the outer wall carbon layer thickness of 0.28 mm), inserting an inner layer sharp cone bottom quartz tube (with the height of 12cm, the inner diameter of 12.5mm, the tube wall thickness of 1.8mm and the inner wall carbon layer thickness of 0.25 mm) into the mixed material, and vacuumizing until the vacuum degree is less than 5 multiplied by 10 - 5 Pa, filling argon, circulating for 3 times, sealing the double-layer quartz tube by flame, and placing the double-layer quartz tube in a vertical tube furnace;
the temperature control program for setting the vertical tube furnace heating thermocouple is as follows: firstly, heating to 1100 ℃ at a speed of 70 ℃/h, and preserving heat for 1200min; then cooling to 760 ℃ at the speed of 0.9 ℃/h, and cooling to 30 ℃ at the speed of 10 ℃/h; finally obtaining the P-type SnSe crystal thermoelectric refrigerating material.
In the specific implementation, according to the obtained P-type SnSe crystal, the crystal is stripped along a cleavage plane, the crystal is cut and polished along the b-axis direction in the crystal plane, and then a Seebeck and resistivity test system and a laser thermal conductivity meter are used for testing the obtained sample, so that the Power Factor (PF) and the thermoelectric performance figure of merit (ZT) of the crystal samples of examples 1-10 and comparative example 1 are obtained;
fig. 2 is data of test results of thermoelectric performance figure of merit (ZT) versus temperature for P-type SnSe crystals prepared in examples 1 to 4 and comparative example 1;
FIG. 3 is data of test results of Power Factor (PF) of the P-type SnSe crystals prepared in examples 1 to 4 and comparative example 1 according to temperature;
as can be seen from comprehensive analysis of fig. 2 to 3, in the P-type Na doped SnSe crystal additionally introduced with Cu provided by the present invention, cu effectively improves the power factor of the material in the test temperature range, indicating that the electrical performance of the sample is greatly improved;
the Cu occupies a large amount of Sn vacancies in the P-type SnSe, promotes the synergistic effect between multivalent bands, optimizes the carrier mobility and the effective mass of the material, and further improves the conductivity and the Seebeck coefficient of the material in a synergistic manner, so that a higher power factor is obtained, and finally a thermoelectric figure of merit which is greatly optimized and improved is obtained;
particularly, the thermoelectric figure of merit of the P-type SnSe crystal reaches more than 1.4 at the room temperature, and the great potential of the P-type SnSe crystal serving as a thermoelectric refrigerating material is fully embodied.
Fig. 4 is data of test results of thermoelectric performance figure of merit (ZT) versus temperature for P-type SnSe crystals prepared in examples 5 to 10;
FIG. 5 is the data of the test results of the Power Factor (PF) of the P-type SnSe crystals prepared in examples 5 to 10 according to the temperature;
comprehensive analysis of figures 4-5 shows that the thermoelectric performance of the Na-doped and Cu-introduced high-performance P-type SnSe crystal provided by the invention is obviously optimized in the whole test temperature range; the high-performance P-type SnSe crystals prepared in examples 5-10 have power factors of more than or equal to 100 mu Wcm at room temperature -1 K -2 The ZT value at room temperature is more than or equal to 1.4; meanwhile, the curves of PF and ZT in figures 4-5 along with the temperature change show that the high-performance P-type SnSe crystal prepared by the method can be obtained by mass duplication, and the thermoelectric performance of the high-performance P-type SnSe crystal is high in repeatability;
the thermoelectric transmission properties of the high-performance P-type SnSe crystals prepared in examples 5 to 10 can be obtained according to fig. 4 to 5, as shown in table 1:
table 1: thermoelectric Transmission Performance of high Performance P-type SnSe Crystal prepared in examples 5-10
From the above examples and comparative examples, the P-type SnSe crystal provided by the invention has excellent thermoelectric transmission performance, and meanwhile, the obtained high-performance P-type SnSe crystal can be duplicated in a large amount, and the thermoelectric performance of the P-type SnSe crystal is high in repeatability.
In practice, on the basis of the above-mentioned high-performance P-type SnSe crystal, it is considered that the conventional thermoelectric properties, particularly room temperature thermoelectric properties (PF≥100μWcm -1 K -2 ZT is greater than or equal to 1.4), so that the material has great potential of becoming a thermoelectric refrigeration material;
cutting and polishing the obtained high-performance P-type SnSe crystal and matching with N-type commercial Bi 2 Te 3 7 pairs of thermoelectric refrigerating devices are prepared to verify whether the thermoelectric refrigerating devices have certain thermoelectric refrigerating capacity, and the thermoelectric refrigerating devices built by the manufactured P-type SnSe thermoelectric refrigerating crystals are shown in fig. 7; placing the obtained high-performance thermoelectric refrigerating device on a temperature difference test platform for electrifying test; the test interface is shown in fig. 6, and the data curve shows that the thermoelectric refrigeration device prepared by the high-performance P-type SnSe crystal can stably realize the refrigeration temperature difference of 61.2K.
In summary, the technical scheme of the patent proposes to place the quartz tip tube inside the flat bottom quartz tube, so as to increase the heat transfer performance inside the crystal, make the inside of the crystal more compact, and solve the difficult problem of preparing a large-volume crystal with a low thermal conductivity system; the high-performance P-type SnSe crystal thermoelectric material prepared by the invention is used as a thermoelectric refrigerating device, so that an excellent refrigerating temperature difference effect is realized; can play an irreplaceable important role in small-volume refrigeration and accurate temperature control scenes; the carrier concentration is optimized by doping Na, and the defect concentration in the crystal is reduced by additionally introducing Cu, so that the carrier mobility is improved, and the conductivity is further improved; the interaction of the material multi-valence band is promoted by the introduction of Cu, and the Seebeck coefficient is improved; the cooperative optimization of the conductivity and the Seebeck coefficient realizes the ultra-high power factor and excellent room temperature performance; so that the power factor PF of the thermoelectric refrigeration material is more than or equal to 100 mu Wcm at room temperature -1 K -2 The ZT value at room temperature is more than or equal to 1.4; snSe crystals obtained based on the invention and the existing commercial Bi 2 Te 3 The built thermoelectric refrigerating device realizes the refrigerating temperature difference of 61.2K.
The foregoing describes in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be made in accordance with the concepts of the invention by one of ordinary skill in the art without undue burden. Therefore, all technical solutions which can be obtained by logic analysis, reasoning or limited experiments based on the prior art by a person skilled in the art according to the inventive concept shall be within the scope of protection defined by the claims.
Claims (9)
1. The preparation method of the thermoelectric refrigeration material based on the P-type SnSe crystal is characterized by comprising the following steps of:
step 1, weighing and mixing Sn, se, cu and Na according to the component proportion of the P-type SnSe crystal thermoelectric refrigeration material to obtain a mixed material;
step 2, carrying out high-temperature fusion synthesis and slow cooling on the mixed material to grow crystals, thereby obtaining the P-type SnSe crystal thermoelectric refrigerating material;
the mixed material of the P-type SnSe crystal is prepared by high-temperature fusion synthesis between an inner quartz tube and an outer quartz tube;
the P-type SnSe crystal thermoelectric refrigerating material is a SnSe material doped with Na and additionally introduced with Cu, and the molar ratio of Sn, se, cu and Na is (1-x): 1: y: x; wherein x is more than or equal to 0.015 and less than or equal to 0.025,0.005, and y is more than or equal to 0.03.
2. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
the high-temperature melt synthesis preparation process in the step 2 is carried out under strict vacuum conditions, and the vacuum degree of the vacuum conditions is less than or equal to 1 multiplied by 10 -4 Pa。
3. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
the double-layer quartz tube is characterized in that the inner-layer quartz tube is a conical quartz tube with a conical bottom, and the height of the inner-layer quartz tube is 11-13 cm; the outer layer quartz tube is a flat bottom quartz tube, and the height is 16-18 cm.
4. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
the outer quartz tube is filled with a mixed material, and the inner quartz tube is placed in the mixed material; the angle range of the bottom cone of the inner quartz tube is 18 degrees or more and theta/2 degrees or less and 20 degrees or less; the wall thickness of the inner quartz tube is not less than 1.5mm.
5. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
in the preparation process of the continuous temperature zone directional solidification method, a double-layer quartz tube filled with mixed materials needs to be vertically placed.
6. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
the temperature program of the vertical high temperature furnace is as follows: firstly, raising the temperature to 1100 ℃ at the rate of 60-80 ℃ per hour, and preserving the temperature for 1200-1500 min to perform melt synthesis; then slowly cooling to 700-800 ℃ at a rate of 0.8-1.2 ℃ per hour for crystal growth; and finally, cooling to 30 ℃ at a rate of 5-10 ℃ per hour to obtain the required P-type SnSe crystal.
7. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
the wall thickness of the outer quartz tube is not less than 1.8mm; the diameter difference between the diameter of the inner wall of the outer quartz tube and the diameter of the outer wall of the inner quartz tube is not smaller than 4mm.
8. The method for producing a thermoelectric refrigerating material as recited in claim 1, wherein,
the outer wall of the inner quartz tube and the inner wall of the outer quartz tube are both coated with a carbon layer for protection, and the thickness of the carbon layer is not less than 0.15mm.
9. The P-type SnSe crystal thermoelectric refrigerating material prepared by the preparation method according to any one of claims 1-8, which is characterized in that,
the thermoelectric refrigerating material can be used for constructing thermoelectric refrigerating devices and is applied to small-volume refrigeration and accurate temperature control scenes.
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