CN112028632B - Non-stoichiometric bismuth telluride-based thermoelectric material and preparation method thereof - Google Patents
Non-stoichiometric bismuth telluride-based thermoelectric material and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of energy materials, and particularly relates to a non-stoichiometric bismuth telluride-based thermoelectric material and a preparation method thereof. The material of the invention has a chemical composition represented by the following general formula: bixSb2‑xTe3+yThe preparation method comprises the following steps: firstly, weighing Bi simple substance powder, Sb simple substance particles and Te simple substance powder raw materials according to the chemical composition of a general formula, and carrying out ball milling treatment to obtain powder; and then carrying out cyclic discharge plasma sintering treatment on the obtained powder for 1 to 5 cycles to obtain a block sample. The bismuth telluride-based thermoelectric material prepared by the method has good crystallinity and compact structure, obviously increases crystal grains and introduces a large amount of dislocation compared with a sample prepared by a traditional mechanical alloying and sintering method, thereby improving the electrical property, reducing the lattice thermal conductivity and having excellent thermoelectric property. Meanwhile, the preparation process is simple and convenient to operate, short in period, free of high-temperature danger, low in energy consumption and wide in application prospect.
Description
Technical Field
The invention belongs to the technical field of energy materials, and particularly relates to a non-stoichiometric bismuth telluride-based thermoelectric material and a preparation method thereof.
Background
Thermoelectric materials can realize the interconversion of heat energy and electric energy, and have great potential in the fields of relieving energy crisis, realizing solid state refrigeration and the like. Compared with the conventional means for converting heat energy and electric energy, the thermoelectric material has the advantages of no mechanical vibration and easy miniaturization, but at present, due to performance limitation, large-scale application is still difficult to realize, so that the improvement of the performance of the thermoelectric material is urgent research. The performance measurement standard of the thermoelectric material is a dimensionless thermoelectric figure of merit ZT value, and the expression is as follows: ZT ═ σ S2T/κ, wherein σ is the electrical conductivity, S is the Seebeck coefficient, T is the absolute temperature, κ is the thermal conductivity, σ S2Commonly referred to as the power factor. In order to obtain high thermoelectric performance, it is required that the material has sigma and S as high as possible and low kappa, and the sigma and S are all related to the transport performance of carriers, so that a strong coupling relationship exists and the individual regulation is difficult. But the lattice thermal conductivity k of one of its constituentsLIt is related to the transmission performance of phonons, so that it can be relatively independently regulated and controlled. Therefore, the basic idea of optimizing thermoelectric materials is to improve the carrier transportThe input performance is simultaneously increased and the scattering of phonons is increased.
Bismuth telluride (Bi)2Te3) The material is the only room temperature thermoelectric material which can be commercially applied at present, and is always concerned by researchers. The solid solution of antimony in bismuth telluride is a common method for realizing high-performance P-type room-temperature thermoelectric material, and the obtained bismuth-antimony-tellurium alloy ((Bi, Sb)2Te3) Also commonly referred to as P-type bismuth telluride. Bismuth telluride belongs to rhombohedral system, and has space group of
Generally, it is considered as a layered structure, in which every five atomic layers are a periodic unit, and each periodic unit is connected by van der waals force, so that bismuth telluride prepared by different methods easily has different degrees of orientation, and the properties thereof are also obviously different. The early bismuth telluride bulk is prepared into bulk crystals by a zone melting method or single crystals by a Bridgman method, and the zone melting method is the mainstream preparation method of commercial bismuth telluride. The bismuth telluride bulk prepared by the two methods has high orientation, shows strong anisotropy, and usually shows high thermoelectric performance in the direction parallel to the atomic layer, but the prepared sample has poor mechanical performance and high interlayer thermal conductivity, so that the thermoelectric performance is prevented from being further improved, and therefore, people adopt a series of preparation methods to prepare polycrystalline bismuth telluride with a nano structure later so as to optimize the mechanical performance and reduce the lattice thermal conductivity.
Generally, the preparation method of polycrystalline bismuth telluride having a nanostructure can be classified into a bottom-up method and a top-down method. The method from bottom to top is usually to synthesize a nanometer precursor by a ball milling method, a melt spinning method or a low-temperature hydrothermal method, and then obtain a block sample by a hot pressing method or a discharge plasma sintering method, wherein the method can retain part of the nanometer structure in the precursor and reduce the grain size; the top-down method generally prepares a block sample first, and then introduces various defects into the block by methods such as mechanical deformation, hot forging and the like. Both methods aim to introduce a large number of defects and nanostructures inside the bulk sample, thereby enhancing mechanical properties and phonon scattering. In recent years, a preparation method called liquid phase sintering has been developed based on the above two methods, and the basic idea is to add a certain component to the raw material to convert the raw material into a eutectic phase in which two phases of solid and liquid coexist and extrude the eutectic phase during sintering, thereby contributing to the introduction of a large amount of dislocations in the bulk. However, at present, various methods have certain disadvantages, and thus, research into these methods is continuously required for improvement.
Chinese patent CN1974079A discloses a method for preparing nano-structure polycrystalline bismuth telluride by combining mechanical alloying with discharge plasma sintering, which adopts a high-energy ball milling method to mechanically alloy element powder, and then obtains the alloyed powder, and the alloyed powder is sintered by a discharge plasma sintering method to obtain the bismuth telluride-based bulk thermoelectric material. Compared with the traditional zone melting method, the method greatly improves the mechanical property of the material, can limit the growth of crystal grains and introduce a large number of defects, reduces the thermal conductivity of the material and finally improves the pyroelectricity. However, the grain size directly prepared by the method is too small, which is not beneficial to the transmission of carriers, and therefore, the electrical property of the material is reduced to a certain extent. Kim et al (Science, Vol.348,2015, 109-114) reported a preparation method in which an excess amount of elemental Te was added to the raw materials so that it formed a eutectic liquid phase and was extruded during spark plasma sintering after treatment using the melt spinning method, but this method was extremely poor in reproducibility.
Disclosure of Invention
The invention aims to provide a non-stoichiometric bismuth telluride-based thermoelectric material and a preparation method thereof, and the preparation method is improved for the existing preparation method of the bismuth telluride-based thermoelectric material so as to improve the electrical property of the bismuth telluride-based thermoelectric material, reduce the lattice thermal conductivity and further improve the dimensionless thermoelectric figure of merit (ZT) value.
The non-stoichiometric bismuth telluride-based thermoelectric material provided by the invention has the chemical composition shown as the following formula:
BixSb2-xTe3+y
wherein x is more than or equal to 0.3 and less than or equal to 0.5, and y is more than or equal to 0 and less than or equal to 1.
The invention provides a preparation method of a nonstoichiometric bismuth telluride-based thermoelectric material, which comprises the following steps:
(1) the chemical composition of the bismuth telluride-based thermoelectric material as defined in claim 1, weighing raw materials of elementary substance powder of Bi, elementary substance particles of Sb and elementary substance powder of Te, placing the raw materials into a ball-milling tank, introducing a protective gas, and performing ball-milling treatment to obtain powder;
(2) and (2) putting the powder obtained in the step (1) into a graphite die, and applying pressure in vacuum to carry out cyclic discharge plasma sintering treatment of repeated temperature rise and drop to obtain the bismuth telluride-based thermoelectric material block.
In the preparation method, the purities of the Bi simple substance powder and the Sb simple substance particles are both more than or equal to 99.99 percent, and the purity of the Te simple substance powder is 99.999 percent by mass.
In the above preparation method, in the step (1), the protective gas is an inert gas.
In the preparation method, the protective gas is argon-hydrogen mixed gas; in the argon-hydrogen mixed gas, the volume fraction of argon is 94-96%, and the volume fraction of hydrogen is 4-6%.
In the preparation method, in the step (1), the ball milling conditions are as follows: the ratio of the grinding balls to the raw materials is (10-20): 1, the rotating speed of the ball mill is 400-480 r/min, and the ball milling time is 3-8 h.
In the preparation method, the vacuum degree of the discharge plasma sintering is 0.1-10 Pa, and the pressure applied by the upper pressure head and the lower pressure head in the furnace chamber is 30-60 MPa.
In the preparation method, in the step (2), the cyclic discharge plasma sintering process of repeatedly increasing and decreasing the temperature includes the following steps:
(1) heating the powder to 380-420 ℃ from room temperature within 5-10 min;
(2) heating to 450-490 ℃ from 380-420 ℃ within 1-4 min;
(3) cooling to 380-420 ℃ from 450-490 ℃ within 1-4 min;
(4) repeating the step (2) and the step (3) for 1 to 5 times;
(5) and finally, cooling to room temperature along with the furnace to obtain the non-stoichiometric bismuth telluride-based thermoelectric material block.
The invention provides a non-stoichiometric bismuth telluride-based thermoelectric material and a preparation method thereof, and the non-stoichiometric bismuth telluride-based thermoelectric material has the advantages that:
1. the invention provides a non-stoichiometric bismuth telluride-based thermoelectric material and a preparation method thereof. The cycle of repeatedly heating and cooling is introduced in the sintering process of the discharge plasma, so that the growth of crystal grains is assisted by a eutectic liquid phase introduced by excessive Te, the eutectic liquid phase can be more effectively expelled to generate a large amount of dislocation, and finally the obtained bismuth telluride-based thermoelectric material block sample has higher electrical property and lower lattice thermal conductivity at the same time, thereby having higher dimensionless thermoelectric figure of merit (ZT) value.
2. The preparation method of the bismuth telluride based thermoelectric material has the advantages of simple and convenient operation, short period, no high temperature danger and low energy consumption, and the finally prepared bismuth telluride based thermoelectric material has good crystallinity, compact structure and high repetition rate. Compared with the traditional mechanical alloying and discharge plasma sintering, the crystal grain of the bismuth telluride-based thermoelectric material prepared by the method is larger, and the electronic transmission is facilitated.
3. The bismuth telluride-based thermoelectric material prepared by the method has a large amount of dislocation inside, and is beneficial to scattering of medium-frequency phonons. The bismuth telluride-based thermoelectric material obtained by the method has higher electrical conductivity and lower lattice thermal conductivity, thereby having higher power factor and thermoelectric figure of merit. When x is 0.4 and y is 0.2 in the structural formula of the material, the dimensionless thermoelectric figure of merit ZT value can reach 1.46 at 348K, and the power factor can reach 4.52 mW.m-1·K-2。
Drawings
Fig. 1 is an X-ray diffraction pattern of bulk samples of the bismuth telluride-based thermoelectric material of examples 1 and 2 of the present invention.
Fig. 2 is a sectional scanning electron microscope photograph of a bismuth telluride-based bulk sample of thermoelectric materials according to examples 1 and 2 of the present invention.
Fig. 3 is a morphology chart of a bismuth telluride-based thermoelectric material block sample prepared according to embodiment 1 of the present invention under a transmission electron microscope: fig. 3(a) is a low-resolution transmission electron microscope photograph of dislocations in the bismuth telluride-based thermoelectric material block sample prepared in example 1, fig. 3(b) is a high-resolution transmission electron microscope photograph of a Sb-rich precipitated phase in the bismuth telluride-based thermoelectric material block sample prepared in example 1, and fig. 3(c) is a low-resolution transmission electron microscope photograph of dislocations pinned by a precipitated phase in the bismuth telluride-based thermoelectric material block sample prepared in example 1.
Fig. 4 is a graph showing the change in electrical conductivity with temperature of bulk samples of the bismuth telluride-based thermoelectric material according to examples 1 to 3 of the present invention.
Fig. 5 is a graph showing the seebeck coefficient with temperature of bulk samples of the bismuth telluride-based thermoelectric material of examples 1 to 3 of the present invention.
Fig. 6 is a graph showing the power factor as a function of temperature for bulk samples of the bismuth telluride-based thermoelectric material of examples 1 to 3 of the present invention.
Fig. 7 is a graph showing the total thermal conductivity as a function of temperature for bulk samples of the bismuth telluride-based thermoelectric material according to examples 1 to 3 of the present invention.
Fig. 8 is a graph of lattice thermal conductivity plus bipolar thermal conductivity as a function of temperature for bulk samples of bismuth telluride-based thermoelectric materials of examples 1 to 3 of the present invention.
Fig. 9 is a graph of the dimensionless thermoelectric figure of merit ZT values as a function of temperature for bulk samples of the bismuth telluride-based thermoelectric materials of examples 1 to 3 of the present invention.
Detailed Description
The non-stoichiometric bismuth telluride-based thermoelectric material provided by the invention has the chemical composition shown as the following formula:
BixSb2-xTe3+y
wherein x is more than or equal to 0.3 and less than or equal to 0.5, and y is more than or equal to 0 and less than or equal to 1.
The invention provides a preparation method of a nonstoichiometric bismuth telluride-based thermoelectric material, which comprises the following steps:
(1) the chemical composition of the bismuth telluride-based thermoelectric material as defined in claim 1, weighing raw materials of elementary substance powder of Bi, elementary substance particles of Sb and elementary substance powder of Te, placing the raw materials into a ball-milling tank, introducing a protective gas, and performing ball-milling treatment to obtain powder;
(2) and (2) putting the powder obtained in the step (1) into a graphite die, and applying pressure in vacuum to carry out cyclic discharge plasma sintering treatment of repeated temperature rise and drop to obtain the bismuth telluride-based thermoelectric material block.
In the preparation method, the purities of the Bi simple substance powder and the Sb simple substance particles are both more than or equal to 99.99 percent, and the purity of the Te simple substance powder is 99.999 percent by mass.
In the above preparation method, in the step (1), the protective gas is an inert gas.
In the preparation method, the protective gas is argon-hydrogen mixed gas; in the argon-hydrogen mixed gas, the volume fraction of argon is 94-96%, and the volume fraction of hydrogen is 4-6%.
In the preparation method, in the step (1), the ball milling conditions are as follows: the ratio of the grinding balls to the raw materials is (10-20): 1, the rotating speed of the ball mill is 400-480 r/min, and the ball milling time is 3-8 h.
In the preparation method, the vacuum degree of the discharge plasma sintering is 0.1-10 Pa, and the pressure applied by the upper pressure head and the lower pressure head in the furnace chamber is 30-60 MPa.
In the preparation method, in the step (2), the cyclic discharge plasma sintering process of repeatedly increasing and decreasing the temperature includes the following steps:
(1) heating the powder to 380-420 ℃ from room temperature within 5-10 min;
(2) heating to 450-490 ℃ from 380-420 ℃ within 1-4 min;
(3) cooling to 380-420 ℃ from 450-490 ℃ within 1-4 min;
(4) repeating the step (2) and the step (3) for 1 to 5 times;
(5) and finally, cooling to room temperature along with the furnace to obtain the non-stoichiometric bismuth telluride-based thermoelectric material block.
In the preparation method of the invention, Bi is addedxSb2-xTe3Adding a proper amount of Te into the mixture to form a knotIn the repeated heating and cooling process of the subsequent cyclic discharge plasma sintering, the crystal grains are greatly increased and a large amount of dislocation is introduced by optimizing the cycle times, so that the power factor of the bismuth telluride-based thermoelectric material is effectively improved, the lattice thermal conductivity is reduced, and the dimensionless thermoelectric figure of merit (ZT) value is finally greatly improved. By adjusting the proportion of Bi and Sb, the carrier concentration can be finely adjusted under different preparation conditions, and the dimensionless thermoelectric figure of merit ZT value is further improved.
The following describes embodiments of the present invention in detail. The following described embodiments are exemplary and are intended to be illustrative of the invention and are not to be construed as limiting the invention.
A non-stoichiometric bismuth telluride-based thermoelectric material according to an embodiment of the present invention has a chemical composition represented by the following general formula (1):
BixSb2-xTe3+y(0.3≤x≤0.5，0≤y≤1) (1)
the bismuth telluride-based thermoelectric material of the above embodiment of the invention is prepared by adding Bi toxSb2-xTe3On the basis, a proper amount of Te is added, the subsequent repeated temperature rise and drop process of the cyclic discharge plasma sintering is combined, and the cycle times are optimized, so that the crystal grains are greatly increased and a large amount of dislocation is introduced, thereby effectively improving the power factor of the bismuth telluride-based thermoelectric material, reducing the lattice thermal conductivity and finally greatly improving the dimensionless thermoelectric figure of merit ZT value. By adjusting the proportion of Bi and Sb, the carrier concentration can be finely adjusted under different preparation conditions, and the dimensionless thermoelectric figure of merit ZT value is further improved.
In the method, inert gas is used as protective gas to ensure that the ball milling tank is in an anaerobic environment, preferably mixed gas of argon and hydrogen is used as protective gas, a small amount of hydrogen is added into the protective gas, and the hydrogen can react with the mixed trace oxygen if the ball milling tank is carelessly mixed with the trace oxygen, so that the ball milling tank is always in the anaerobic environment. In the method, the raw materials are treated by a ball milling method to obtain powder, the operation is simple and convenient, the period is short, no high-temperature danger exists, the energy consumption is low, and the proper ball milling condition is selected to ensure the full reaction among the raw materials.
In the method, proper spark plasma sintering conditions are selected, and the powder is treated by a spark plasma sintering method, so that the bismuth telluride-based thermoelectric material block has the advantages of good crystallinity, compact structure, high repetition rate and excellent thermoelectric performance. At the same time, a proper circulation process is adopted to ensure that excessive Bi is addedxSb2-xTe3the-Te eutectic phase can realize uniform distribution in the sintering process and is further extruded, so that the grain size of the obtained bismuth telluride-based thermoelectric material is increased, and a large amount of dislocation is introduced into the bismuth telluride-based thermoelectric material.
According to the method, for example, x is 0.45, y is 0.2, the number of times of sintering of the cyclic discharge plasma is 1 to 5, preferably 4 times of cycle, the electric conductivity and the power factor are obviously improved, the lattice thermal conductivity is reduced, and the dimensionless thermoelectric figure of merit ZT value is improved. Further adjustment is made to make x equal to 0.4, and at 348K, the power factor can be increased to 4.52 mW.m-1·K-2The lattice thermal conductivity can be reduced to 0.59 W.m-1·K-1The dimensionless thermoelectric figure of merit ZT value can be as high as 1.46.
Specific embodiments of the method of the present invention are described below with reference to the accompanying drawings:
the elemental powders of Bi and the elemental particles of Sb used in the examples and the comparative examples of the present invention were produced by shanghai alading biochemical technologies, ltd, and the elemental powders of Te were produced by zhongnuo new materials (beijing) technologies, ltd.
Example 1:
is represented by the chemical formula Bi0.45Sb1.55Te3.2(i.e. of the formula Bi)xSb2-xTe3+yIn the stoichiometric ratio of x ═ 0.45 and y ═ 0.2, 15g of the raw material mixture was weighed, specifically 2.0366 g of the simple substance Bi powder (purity 99.99%), 4.0948 g of the simple substance Sb particles (purity 99.99%) and 8.8687 g of the simple substance Te powder (purity 99.999%).
Putting the weighed mixture into a stainless steel ball milling tank, wherein the mass ratio of stainless steel grinding balls to the raw materials is 20:1, introducing argon-hydrogen mixed gas serving as protective gas into the ball milling tank, wherein the volume content of hydrogen is 5%, the volume content of argon is 95%, and performing ball milling for 6h in a planetary ball mill (QM-3SP2, Nanjing university instrument factory) at the rotating speed of 450 r/min.
Placing the powder into a graphite mold, compacting, placing into a discharge plasma sintering furnace (SPS), heating to 420 deg.C in a heating stage for 7min under vacuum degree of 5Pa and longitudinal pressure of 50MPa, and circulating for 4 times, wherein the heating stage of each circulation is 2min from 420 deg.C to 470 deg.C, the cooling stage of each circulation is 3min from 470 deg.C to 420 deg.C, and cooling to obtain circulation 4 times of Bi with general formula0.45Sb1.55Te3.2The block of thermoelectric material of (1).
After the surface of the bismuth telluride-based thermoelectric material block prepared in the embodiment is polished by using sand paper, phase identification and microstructure characterization are performed, and a thermoelectric performance test is performed. The X-ray diffraction pattern of the bismuth telluride-based thermoelectric material prepared in the present example is shown in fig. 1, the cross-sectional scanning electron microscope photograph is shown in fig. 2, and the morphology under the transmission electron microscope is shown in fig. 3. The electric conductivity of the bismuth telluride-based thermoelectric material prepared in the embodiment along with the temperature change is shown in fig. 4, the seebeck coefficient is shown in fig. 5, the power factor is shown in fig. 6, the total thermal conductivity is shown in fig. 7, the lattice thermal conductivity and the bipolar thermal conductivity are shown in fig. 8, and the dimensionless thermoelectric figure of merit ZT value is shown in fig. 9.
Fig. 1 shows that the material prepared is pure phase bismuth telluride with a small amount of excess Te phase remaining, but the peak of the Te phase is reduced after 4 cycles. As can be seen from FIG. 2, the grain size of the sample after 4 cycles was 20 μm or more, and the sample showed significant growth relative to the sample after 2 cycles. As can be seen from fig. 3, a large number of dislocations and Sb-rich nano precipitated phases exist in the sample after 4 cycles, and meanwhile, the nano precipitated phases can pin the dislocations and further propagate the dislocations, which can effectively reduce the lattice thermal conductivity of the sample. As can be seen from fig. 4 to 9, the conductivity of the sample decreased with increasing temperature for 4 cycles, and was significantly increased relative to the conductivity of the sample increased for 2 cycles; the Seebeck coefficient is increased firstly and then reduced along with the temperature rise, and compared with the sample circulating for 2 times, the Seebeck coefficient is reduced in the low-temperature area and the peak value moves to the high-temperature area; the power factor is reduced along with the temperature rise, and is greatly improved relative to the sample circulating for 2 times; the thermal conductivity is firstly reduced and then increased along with the temperature increase, and the thermal conductivity is increased but not large compared with that of a sample which is circulated for 2 times; the lattice thermal conductivity and the bipolar thermal conductivity increase along with the temperature increase, and are obviously reduced relative to the sample which is circulated for 2 times; the nondimensional thermoelectric figure of merit ZT value rises first and then falls with the temperature rise, and is increased by a wide margin to 1.39 at 348K compared with the sample circulating for 2 times.
Example 2
Is represented by the chemical formula Bi0.45Sb1.55Te3.2(i.e., Bi of the general formula (1))xSb2-xTe3+yIn the stoichiometric ratio of x ═ 0.45 and y ═ 0.2, 15g of the raw material mixture was weighed, specifically 2.0366 g of the simple substance Bi powder (purity 99.99%), 4.0948 g of the simple substance Sb particles (purity 99.99%) and 8.8687 g of the simple substance Te powder (purity 99.999%).
Putting the weighed mixture into a stainless steel ball milling tank, wherein the mass ratio of stainless steel grinding balls to the raw materials is 20:1, introducing argon-hydrogen mixed gas serving as protective gas into the ball milling tank, wherein the volume content of hydrogen is 5%, the volume content of argon is 95%, and performing ball milling for 6h in a planetary ball mill (QM-3SP2, Nanjing university instrument factory) at the rotating speed of 450 r/min.
Placing the powder into a graphite mold, compacting, placing into a discharge plasma sintering furnace (SPS), heating to 420 deg.C for 7min at a vacuum degree of 5Pa and a longitudinal pressure of 50MPa, and performing 2 cycles, wherein the temperature of each cycle is increased from 420 deg.C to 470 deg.C for 2min, the temperature of each cycle is decreased from 470 deg.C to 420 deg.C for 3min, and cooling to obtain 2 cycles of Bi represented by general formula0.45Sb1.55Te3.2The block of thermoelectric material of (1).
The X-ray diffraction pattern of the bismuth telluride-based thermoelectric material prepared in this example is shown in fig. 1, and the cross-sectional scanning electron micrograph is shown in fig. 2. The electric conductivity of the bismuth telluride-based thermoelectric material prepared in the embodiment along with the temperature change is shown in fig. 4, the seebeck coefficient is shown in fig. 5, the power factor is shown in fig. 6, the total thermal conductivity is shown in fig. 7, the lattice thermal conductivity and the bipolar thermal conductivity are shown in fig. 8, and the dimensionless thermoelectric figure of merit ZT value is shown in fig. 9.
Fig. 2 shows that the prepared material is pure phase bismuth telluride with a small amount of residual excess Te phase. In FIG. 2, the crystal grain size is about 2 μm. As can be seen from fig. 4 to 9, the conductivity of the sample decreased with increasing temperature for 2 cycles; the Seebeck coefficient increases first and then decreases with increasing temperature; the power factor decreases with increasing temperature; the thermal conductivity is firstly reduced and then increased along with the temperature increase; lattice thermal conductivity plus bipolar thermal conductivity increases with increasing temperature; the dimensionless thermoelectric figure of merit ZT value decreases with increasing temperature and is at most 1.13 at 308K.
Example 3
Is represented by the chemical formula Bi0.4Sb1.6Te3.2(i.e., Bi of the general formula (1))xSb2-xTe3+yIn the stoichiometric ratio of x ═ 0.4 and y ═ 0.2, 15g of the raw material mixture was weighed, specifically 1.8217 g of the simple substance Bi powder (purity 99.99%), 4.2536 g of the simple substance Sb particles (purity 99.99%) and 8.9247 g of the simple substance Te powder (purity 99.999%).
Putting the weighed mixture into a stainless steel ball milling tank, wherein the mass ratio of stainless steel grinding balls to the raw materials is 20:1, introducing argon-hydrogen mixed gas serving as protective gas into the ball milling tank, wherein the volume content of hydrogen is 5%, the volume content of argon is 95%, and performing ball milling for 6h in a planetary ball mill (QM-3SP2, Nanjing university instrument factory) at the rotating speed of 450 r/min.
Placing the powder into a graphite mold, compacting, placing into a discharge plasma sintering furnace (SPS), heating to 420 deg.C in a heating stage for 7min under vacuum degree of 5Pa and longitudinal pressure of 50MPa, and circulating for 4 times, wherein the heating stage of each circulation is 2min from 420 deg.C to 470 deg.C, the cooling stage of each circulation is 3min from 470 deg.C to 420 deg.C, and cooling to obtain circulation 4 times of Bi with general formula0.4Sb1.6Te3.2The block of thermoelectric material of (1).
The electric conductivity of the bismuth telluride-based thermoelectric material prepared in the embodiment along with the temperature change is shown in fig. 4, the seebeck coefficient is shown in fig. 5, the power factor is shown in fig. 6, the total thermal conductivity is shown in fig. 7, the lattice thermal conductivity and the bipolar thermal conductivity are shown in fig. 8, and the dimensionless thermoelectric figure of merit ZT value is shown in fig. 9.
As can be seen from fig. 4 to 9, the sample conductivity decreases with increasing temperature; the Seebeck coefficient increases first and then decreases with increasing temperature; the power factor decreases with increasing temperature; the thermal conductivity decreases and then increases with increasing temperature(ii) a Lattice thermal conductivity plus bipolar thermal conductivity increases with increasing temperature; the nondimensional thermoelectric figure of merit ZT value increases and then decreases with increasing temperature. The optimal dimensionless thermoelectric figure of merit ZT value is 1.46 at 348K, and the power factor is 4.52 mW.m-1·K-2The lattice thermal conductivity plus the bipolar thermal conductivity is 0.59 W.m-1·K-1。
The implementation 1 and 2 of the invention adjust the temperature rise and drop cycle times in the discharge plasma sintering process, the bismuth telluride-based thermoelectric material prepared by 4 cycles has excellent thermoelectric performance, the electrical conductivity and the power factor are effectively improved, the lattice thermal conductivity is reduced, and finally the dimensionless thermoelectric figure of merit ZT value is greatly improved. To the general formula Bi0.4Sb1.6Te3.2The sample is prepared by a discharge plasma sintering method of combining mechanical alloying with cyclic temperature rise and drop for 4 times, and more excellent thermoelectric property is obtained.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (6)
1. A preparation method of a nonstoichiometric bismuth telluride-based thermoelectric material is characterized in that,
the nonstoichiometric bismuth telluride-based thermoelectric material has a chemical composition shown as the following formula:
BixSb2-xTe3+y
wherein x is more than or equal to 0.3 and less than or equal to 0.5, and y is more than or equal to 0 and less than or equal to 1;
the preparation method comprises the following steps:
(1) weighing raw materials of Bi simple substance powder, Sb simple substance particles and Te simple substance powder according to the chemical composition of the bismuth telluride-based thermoelectric material, putting the raw materials into a ball-milling tank, introducing protective gas, and carrying out ball-milling treatment to obtain powder;
(2) putting the powder obtained in the step (1) into a graphite die, applying pressure in vacuum, and performing cyclic discharge plasma sintering treatment of repeated temperature rise and drop to obtain a non-stoichiometric bismuth telluride-based thermoelectric material block;
the cyclic discharge plasma sintering treatment process of repeatedly heating and cooling comprises the following steps:
(a) heating the powder to 380-420 ℃ from room temperature within 5-10 min;
(b) heating to 450-490 ℃ from 380-420 ℃ within 1-4 min;
(c) cooling to 380-420 ℃ from 450-490 ℃ within 1-4 min;
(d) repeating the step (2) and the step (3) for 1 to 5 times;
(e) and finally, cooling to room temperature along with the furnace to obtain the non-stoichiometric bismuth telluride-based thermoelectric material block.
2. The method for producing a bismuth telluride-based thermoelectric material as claimed in claim 1, wherein the purity of both the elementary substance powder of Bi and the elementary substance particle of Sb is 99.99% or more, and the purity of the elementary substance powder of Te is 99.999% by mass.
3. The method for preparing a bismuth telluride-based thermoelectric material as set forth in claim 1 wherein in the step (1), the protective gas is an inert gas.
4. The method for producing a bismuth telluride-based thermoelectric material as claimed in claim 1, wherein the protective gas is an argon-hydrogen mixed gas; in the argon-hydrogen mixed gas, the volume fraction of argon is 94-96%, and the volume fraction of hydrogen is 4-6%.
5. The method for preparing the bismuth telluride-based thermoelectric material as set forth in claim 1, wherein in the step (1), the ball milling conditions are as follows: the ratio of the grinding balls to the raw materials is (10-20): 1, the rotating speed of the ball mill is 400-480 r/min, and the ball milling time is 3-8 h.
6. The method for preparing the bismuth telluride-based thermoelectric material as set forth in claim 1, wherein in the step (2), the degree of vacuum of the spark plasma sintering is 0.1 to 10Pa, and the pressure applied by an upper pressure head and a lower pressure head in a furnace chamber is 30 to 60 MPa.
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| CN115521148A (en) * | 2022-09-22 | 2022-12-27 | 广西自贸区见炬科技有限公司 | Cu doped (Bi, sb) 2 Te 3 Method for preparing thermoelectric material and product thereof |
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