CN111689512A - In-doped Cu-S-based thermoelectric material and preparation method thereof - Google Patents
In-doped Cu-S-based thermoelectric material and preparation method thereof Download PDFInfo
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Abstract
The invention provides an In-doped Cu-S-based thermoelectric material and a preparation method thereof, wherein the chemical general formula of the Cu-S-based thermoelectric material is 2 x (1-y) Cu2S+yCuInS2Wherein y is more than or equal to 0.002 and less than or equal to 0.10. The invention utilizes three-step ball milling, realizes that a uniformly dispersed nano second phase is introduced into a Cu-S-based thermoelectric material in situ by reasonably setting ball milling parameters and doping element content, forms a compact block material after being rapidly sintered by utilizing radio frequency induction hot-pressing equipment at proper temperature and pressure, and ensures that uniformly dispersed second phase nano crystal grains still exist and have coherent and semi-coherent relation with a matrix, so that current carriers smoothly pass without influencing electrical property, and phonons are severely scattered to greatly reduce thermal conductivity, thereby ensuring that the material has excellent thermoelectric property, and the existence of the second phase nano crystal boundaryThe long-range diffusion of Cu ions is hindered, so that the thermal stability of the material is enhanced. The preparation method is simple in preparation process, easy for mass production and good in controllability.
Description
Technical Field
The invention belongs to the fields of chemistry, chemical engineering and material science, and particularly relates to an In-doped Cu-S-based thermoelectric material and a preparation method thereof.
Background
Thermoelectric materials can be made into refrigerators which do not need moving parts or freon, can realize accurate temperature control and micro-area refrigeration, and can also be used as temperature regulation systems of optical communication laser diodes and infrared sensors, and the like, but the lower conversion efficiency of thermoelectric devices restricts the market application of the thermoelectric devices2σ/κ) T, where α represents seebeck coefficient, σ is electrical conductivity, κ is thermal conductivity, and T is absolute temperature the larger ZT value of a material indicates better thermoelectric performance.
At present, the Cu-S-based thermoelectric material is a thermoelectric material suitable for the field of medium temperature (400-3) Compared with the prior art, the composite material has many advantages, such as no toxicity, no pollution, low price, light weight and the like. However, most of the existing Cu-S-based thermoelectric materials with better performance are prepared by combining a long-time solid-state reaction method with Spark Plasma Sintering (SPS), which is complex in process and long in time consumption, is not easy to control volatilization of S in a long-time high-temperature process and directional migration and diffusion of Cu in an SPS process, is not favorable for large-scale industrial production, and has high cost. On the other hand, the Cu-S based thermoelectric material hasThe thermoelectric performance is very high, but in the sample under the high-temperature and long-term large-current state, the directional migration of Cu ions can be generated, so that the performance of the device is deteriorated. Although some processes have been developed to improve the stability of the material, the highest ZT value tends to be low.
Therefore, how to provide an In-doped Cu-S-based thermoelectric material and a preparation method thereof are necessary to solve the above problems In the prior art.
Disclosure of Invention
In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide an In-doped Cu-S-based thermoelectric material and a method for preparing the same, which are used to solve the problems of low thermoelectric performance, poor stability, etc. of the thermoelectric material In the prior art.
To achieve the above and other related objects, the present invention provides an In-doped Cu-S-based thermoelectric material having a general chemical formula of 2 x (1-y) Cu2S+yCuInS2Wherein y is more than or equal to 0.002 and less than or equal to 0.10.
As an alternative scheme of the invention, the value range of y is more than or equal to 0.005 and less than or equal to 0.03.
As an alternative of the invention, the CuInS2The Cu as a second phase of the Cu-S based thermoelectric material2S is used as a matrix of the Cu-S based thermoelectric material, wherein the second phase and the matrix have at least one of a coherent relationship and a semi-coherent relationship.
The invention also provides a preparation method of the In-doped Cu-S-based thermoelectric material, which comprises the following steps:
providing a first elementary substance Cu raw material and an elementary substance S raw material, and carrying out first mixing ball milling to obtain a first ball-milled product;
adding a simple substance In raw material into the first ball-milled product, and carrying out second mixing ball milling to obtain a second ball-milled product;
adding a second simple substance Cu raw material into the second ball-milled product, and carrying out third mixing ball milling to obtain a third ball-milled product;
and carrying out hot-pressing sintering on the third ball-milling product by utilizing a radio frequency induction hot-pressing device to obtain the In-doped Cu-S-based thermoelectric material with the nano structure.
As an alternative of the invention, the mole ratio of the first elementary Cu raw material to the elementary S raw material is between 1:1.9 and 2.1, and the first ball-milled product at least comprises CuS2Wherein, the process of performing the first mixed ball milling comprises the following formula of Cu +2S ═ CuS2The reaction is carried out.
As an alternative of the present invention, the molar ratio of the first ball-milled product to the elemental In feedstock comprises 1: y, the second ball-milled product at least comprises CuS2And CuInS2Wherein, the process of carrying out the second mixed ball milling comprises CuS according to a formula2+y In＝(1-y)CuS2+y CuInS2The reaction is carried out.
As an alternative of the invention, the second elemental Cu raw material is added in a corresponding amount in accordance with the composition to be designed, and the third ball-milling product comprises at least Cu2S and CuInS2Wherein, the third mixing ball milling process comprises CuS according to the formula (1-y)2+y CuInS2+3*(1-y)Cu＝2*(1-y)Cu2S+y CuInS2The reaction is carried out.
As an alternative of the invention, the third ball-milled product has the chemical formula Cu2-xSInyWherein x is more than or equal to 0 and less than or equal to 0.1.
As an alternative of the present invention, during at least one of the first mixing ball milling, the second mixing ball milling and the third mixing ball milling, a step of adding a dispersing agent is further included, wherein the dispersing agent includes n-hexane, during the mixing ball milling, the mixture is sealed in a ball milling tank according to a ball-to-material ratio of 12:1-18:1, the rotation speed of the mixing ball milling is between 600rpm and 1000rpm, and the time of the mixing ball milling is between 30min and 50 h.
As an alternative scheme of the invention, the power frequency of the radio frequency induction hot-pressing equipment is more than or equal to 100kHz, the third ball-milled product is loaded into a high-pressure-resistant graphite mold, and then the radio frequency induction hot-pressing equipment is utilized to carry out hot pressing for 10min to 55min under the conditions of inert gas protection, the temperature of 650 ℃ to 850 ℃ and the pressure of 35MPa to 95MPa, so as to obtain the In-doped Cu-S-based thermoelectric material with the nano structure.
As an alternative of the present invention, the inert gas in the rf induction hot-pressing apparatus includes at least one of nitrogen and argon, and the pressure is 0.08 to 5.5 atmospheres.
As described above, the In-doped Cu-S-based thermoelectric material and the preparation method thereof realize the In-situ introduction of the uniformly dispersed nano second phase In the Cu-S-based thermoelectric material by utilizing three-step ball milling and reasonably setting ball milling parameters and doping element content, form a compact block material after being rapidly sintered by utilizing radio frequency induction hot-pressing equipment under proper temperature and pressure, enable the uniformly dispersed second phase nano crystal grains to still exist and have coherent and semi-coherent relations with the matrix, enable current carriers to smoothly pass without influencing electrical properties, and enable phonons to be severely scattered to cause great reduction In thermal conductivity, thereby enabling the material to have excellent thermoelectric properties, and the existence of the second phase nano crystal boundary hinders the long-range diffusion of Cu ions, so that the thermal stability of the material is enhanced. The preparation method is simple in preparation process, easy for mass production and good in controllability.
Drawings
Fig. 1 is a schematic diagram illustrating a process for preparing an In-doped Cu-S-based thermoelectric material according to an exemplary embodiment of the present invention.
Fig. 2 shows the microstructure of the Cu — S based thermoelectric materials obtained in comparative example 1 and example 1 of the present invention.
Fig. 3 shows the temperature-dependent curves of the electrical conductivity, the power factor, the thermal conductivity, and the ZT value of the Cu — S-based thermoelectric materials in comparative examples 1 to 2 and examples 1 to 2 according to the present invention.
Fig. 4 shows the thermal conductivity of the Cu — S based thermoelectric material according to the present invention in examples 3 to 6 as a function of temperature.
Fig. 5 shows a TEM image of a Cu-S based thermoelectric material in an example of the present invention.
Description of the element reference numerals
S1-S4
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 4. It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the form, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
The invention provides an In-doped Cu-S-based thermoelectric material, which has a chemical general formula of 2 x (1-y) Cu2S+yCuInS2Wherein y is more than or equal to 0.002 and less than or equal to 0.10.
By way of example, y is in a value range of 0.005 ≦ y ≦ 0.03.
Specifically, the nominal chemical formula component of the In-doped Cu-S-based thermoelectric material can be Cu1.99SIn0.0025、 Cu1.985SIn0.005、Cu1.9775SIn0.0075、Cu1.97SIn0.01And the like.
As an example, the CuInS2The Cu as a second phase of the Cu-S based thermoelectric material2S is used as a matrix of the Cu-S based thermoelectric material, wherein the second phase and the matrix have at least one of a coherent relationship and a semi-coherent relationship.
In particular, the invention provides an In-doped Cu-S-based nano polycrystalline thermoelectric material, and the high-performance Cu-S-based thermoelectric material with a dispersed nano structure is formedWherein, in one example, the CuInS2As a second phase of the Cu-S based thermoelectric material, the Cu2S is used as a matrix of the Cu-S based thermoelectric material, wherein the second phase has at least one of a coherent relationship and a semi-coherent relationship with the matrix, as shown In fig. 5, fig. 5(a) is a TEM image of the Cu-S based nano-polycrystalline thermoelectric material In which In is doped In an amount of 1%, and fig. 5(b) is a TEM image of the Cu-S based nano-polycrystalline thermoelectric material In which In is doped In an amount of 1.5%, and the relation between the matrix and the second phase can be seen. The material is suitable for the fields of nano science and technology, and has important application prospects in the aspects of improving the performance of thermoelectric materials and enhancing the thermal stability of the materials.
As shown In fig. 1, the present invention also provides a method for preparing an In-doped Cu-S-based thermoelectric material according to any one of the above schemes, the method comprising the steps of:
providing a first elementary substance Cu raw material and an elementary substance S raw material, and carrying out first mixing ball milling to obtain a first ball-milled product;
adding a simple substance In raw material into the first ball-milled product, and carrying out second mixing ball milling to obtain a second ball-milled product;
adding a second simple substance Cu raw material into the second ball-milled product, and carrying out third mixing ball milling to obtain a third ball-milled product;
and carrying out hot-pressing sintering on the third ball-milling product by utilizing a radio frequency induction hot-pressing device to obtain the In-doped Cu-S-based thermoelectric material with the nano structure.
Firstly, as shown in S1 in fig. 1, providing a first elemental Cu raw material and an elemental S raw material, and performing a first mixed ball milling to obtain a first ball-milled product;
by way of example, the molar ratio of the first elemental Cu feedstock to the elemental S feedstock is between 1:1.9 and 2.1, preferably 1:2, and the first ball-milled product includes at least CuS2Wherein, the first mixing ball milling process comprises the following formula of Cu +2S ═ CuS2The reaction is carried out.
Illustratively, the first mixing ball milling process further comprises a step of adding a dispersing agent, wherein the dispersing agent comprises n-hexane, the mixing ball milling process is carried out, the mixture is sealed in a ball milling tank according to a ball-to-material ratio of 12:1-18:1, the rotation speed of the mixing ball milling process is 600rpm-1000rpm, such as 700rpm, and the mixing ball milling time is 30min-50h, such as 250min-350 min.
Specifically, the powder sample required by the preparation of the block thermoelectric material is divided into three steps to carry out mechanical synthesis reaction in a physical mode, namely a three-step method, and firstly, the first step, precursor synthesis, is carried out; in an example, firstly, copper powder (99%) and sulfur powder (99.5%) are weighed according to a proportioning scheme with a stoichiometric ratio of 1:2 and then mixed, wherein, it should be noted that the simple substance mentioned in the present invention, not a strictly pure simple substance, can be 99%, 99.5%, etc. which can be understood by those skilled in the art, and should not be limited excessively, the proportioned mixed powder is added into a ball mill (such as Nanjing university ball mill), then the raw material and stainless steel small balls are put into a stainless steel ball mill pot according to a proportioning of 1:12, the stainless steel small balls adopt two specifications for mixing and have diameters of 10mm and 6mm respectively, in order to obtain smaller and more uniform powder, an appropriate amount of a grinding aid, namely the dispersing agent, is n-hexane, the grinding aid adopted in the present experiment is sealed and then placed on the ball mill for ball milling, the rotation speed of the ball mill is set to 600rpm, the first synthesis step took 300 minutes, and the reaction occurred: cu +2S ═ CuS2。
Then, as shown In S2 In fig. 1, adding an In raw material to the first ball-milled product, and performing a second mixed ball-milling to obtain a second ball-milled product;
by way of example, the molar ratio of the first ball-milled product to the elemental In feedstock comprises 1: y, the second ball-milled product at least comprises CuS2And CuInS2Wherein, the process of carrying out the second mixed ball milling comprises CuS according to a formula2+yIn＝ (1-y)CuS2+y CuInS2The reaction is carried out.
Illustratively, the second mixing ball milling process further comprises a step of adding a dispersing agent, wherein the dispersing agent comprises n-hexane, the mixing ball milling process is carried out by sealing the mixture into a ball milling tank according to a ball-to-material ratio of 12:1-18:1, the rotation speed of the mixing ball milling process is 600rpm-1000rpm, such as 700rpm, and the mixing ball milling time is 30min-50h, such as 250min-350 min.
Specifically, the second step, intermediate synthesis, is carried out; adding doped In element into the precursor prepared In the previous step, wherein the addition amount accounts for y% of the total sample, and In one example, the addition amount is CuS2In ratio to In according to CuS2The proportion of + y In, the material ratio In the nodular graphite pot is 18:1, and In the mechanized alloying process, the rotating speed of the ball mill is 600 revolutions per minute for 30 minutes; reaction is carried out: CuS2+y％In＝(1-y)CuS2+y％CuInS2。
Continuing, as shown in S3 in fig. 1, adding a second simple substance Cu raw material into the second ball-milled product, in an example, the molar ratio of the second simple substance Cu raw material to the first simple substance Cu raw material in the first step ball milling of the second simple substance Cu raw material is between 2.5:1 and 3.5:1, and performing third mixed ball milling to obtain a third ball-milled product;
as an example, the second elemental Cu raw material is added in a corresponding amount according to the composition to be designed, and the third ball-milling product comprises at least Cu2S and CuInS2Wherein, the third mixing ball milling process comprises CuS according to the formula (1-y)2+y CuInS2+3*(1-y)Cu＝2*(1-y)Cu2S+y CuInS2The reaction is carried out.
Illustratively, the third mixing and ball milling process further comprises a step of adding a dispersing agent, wherein the dispersing agent comprises n-hexane, the mixing and ball milling process is carried out by sealing the mixture into a ball milling tank according to a ball-to-material ratio of 12:1-18:1, the rotation speed of the mixing and ball milling process is 600rpm-1000rpm, such as 700rpm, and the mixing and ball milling time is 30min-50h, such as 250min-350 min.
Specifically, the third step is carried out, and the final product is synthesized; this step is the final step in the physical reaction process of the mechanized alloy, and in one example, the ratio of the copper-sulfur element added before the addition is countedAccording to the total addition amount of Cu: s, weighing the mass of copper according to a molar ratio of 2:1, carrying out the reaction of the last step, wherein the adding content is the total adding content molar ratio obtained by superposing the molar amounts of the copper and the sulfur after integrating the three steps, mixing and adding the weighed copper powder into a nodular graphite tank in which a reaction intermediate of the second step is positioned for reaction, wherein the material ratio in the nodular graphite tank is 12:1, and the rotating speed of a ball mill is set to be 600 revolutions per minute for 300 minutes; reaction is carried out: (1-y) CuS2+y CuInS2+3*(1-y)Cu＝2*(1-y)Cu2S+yCuInS2。
Finally, as shown In S4 In fig. 1, the third ball-milled product was subjected to hot-press sintering using a radio frequency induction hot-press apparatus to obtain an In-doped Cu — S-based thermoelectric material having a nanostructure.
As an example, the power frequency of the radio frequency induction hot-pressing device is greater than or equal to 100 kHz.
As an example, after the third ball-milled product is loaded into a high pressure resistant graphite mold, hot-pressing for 10min to 55min, such as 12min or 18min, under the conditions of inert gas protection, temperature of 650 ℃ to 850 ℃ and pressure of 35Mpa to 95Mpa by using a radio frequency induction hot-pressing device, so as to obtain the In-doped Cu-S-based thermoelectric material with a nano structure.
As an example, the inert gas in the rf induction hot-pressing apparatus includes at least one of nitrogen and argon, and the pressure is 0.08 to 5.5 atmospheres.
As an example, the speed of hot pressing the third ball-milled product with the radio frequency induction hot pressing device is between 24 ℃/min-144 ℃/min, for example, the speed of the rapid hot pressing is a temperature rise from 100 ℃ to 820 ℃ in a time range of 5min to 30min, wherein the nanostructure may be a second phase CuInS2The nano-structure is obtained by combining various factors, such as doping content, hot pressing temperature and speed, ball milling three-step preparation and the like.
Specifically, in an example, the method further includes a step of removing the dispersant (grinding aid) in the third ball-milled product after the third mixed ball-milling for hot-pressing, and may further include a step of subsequently utilizing a radio frequency induction hot-pressing device to hot-press the washed and dried third ball-milled product.
Finally, the final powder product generated by the reaction is dried, screened and weighed, and added into a graphite grinding tool with the diameter of 12.7mm to prepare hot pressing.
As an example, the third ball-milled product has the chemical formula (expressed herein as the nominal composition after reaction) Cu2-xSInyWherein x is more than or equal to 0 and less than or equal to 0.1. In one example, the material may be Cu2-xThe doping in S can correspondingly reduce the addition of Cu, so that the final proportioning nominal component is Cu2-xThe value range of x is more than or equal to 0 and less than or equal to 0.1, and in one example, the first ball-milled product obtained after the first mixed ball milling comprises Cu1.8S、Cu1.91S、Cu1.96And S and the like, and then carrying out the second mixed ball milling and the third mixed ball milling to obtain the final In-doped Cu-S-based thermoelectric material.
Among them, Cu of better performance in the comparative example2-xCu prepared by adopting S-based thermoelectric material as melting and solidifying technology1.97S or Cu prepared by combination of melting sintering and discharge plasma sintering (SPS)1.97The highest ZT of 1000K S is 1.9 and 1.7, respectively, the thermoelectric property is relatively poor, and In another comparative example, In is subjected to ball milling2S3And Cu2S, uniformly mixing and performing hot-pressing sintering on the mixture by using SPS (semi-solid phase sintering), so that the thermal stability of the obtained material is greatly improved; however, In of this type2S3-Cu2The highest ZT of the S composite is only 1.23 at 850K.
Aiming at the defects in the prior art, the invention is simpler, more convenient and more effective in improving Cu2-xThe invention provides an In-doped Cu-S-based thermoelectric material which has the advantages of simple process, short preparation period, capability of effectively avoiding S volatilization and Cu ion directional migration, higher ZT value and better thermal stability and a preparation method thereof. The invention utilizes three-step ball milling to uniformly dope a proper amount of In element into a Cu-S system and form nano powder, so that the crystal grains of the mixed product are fineSmall and uniform, and can avoid S volatilization under high temperature synthesis; by combining with the radio frequency induction rapid hot-pressing sintering method, the directional migration of Cu caused by the direct application of current to the raw material in SPS can be avoided, and Cu-S base (such as Cu) can be further promoted2-xS-based) thermoelectric material in situ generates nano second phase substances which are dispersed and distributed, and the crystal grains and the matrix have coherent or semi-coherent orientation. This particular structure makes Cu2The ZT value of the S system can be as high as 2.0 at a lower temperature of 773K. Meanwhile, the nano second phase substance effectively blocks the directional migration of Cu ions, so that the thermal stability of the material is improved. Related work is not reported in documents to date.
The In-doped Cu — S-based thermoelectric material and the method for preparing the same according to the present invention will be described In detail with reference to specific examples.
Example 1:
preparation of Cu by ball milling and radio frequency induction rapid hot pressing in three steps2S +1 mol% In polycrystalline thermoelectric material:
step 1), weighing simple substance raw materials Cu and S according to a molar ratio of 1:2, using normal hexane as a grinding aid, packaging in an inert atmosphere with a ball mass ratio of 18:1, then performing ball milling by using parameters of a rotating speed of 600rpm and a time of 300min, and obtaining a formula Cu + 2S-CuS2Formation of CuS2A compound;
step 2), adding 1 mol% of In raw material into the obtained product In the step 1), packaging In inert atmosphere, carrying out mixed ball milling, and carrying out CuS according to a formula2+0.01In＝0.99CuS2+0.01CuInS2Forming a mixed product;
step 3), adding a corresponding amount of Cu raw materials into the product obtained in the step 2) according to the final design components, packaging in an inert atmosphere, performing ball milling by using the parameters of the rotating speed of 600rpm and the time of 300min, and obtaining the Cu-based alloy according to the formula of 0.99CuS2+0.01CuInS2+2.97Cu＝1.98Cu2S+0.01CuInS2Forming a final product;
step 4), under the protection of argon, performing hot pressing on the 1.98Cu by using a radio frequency induction hot pressing device under the conditions of hot pressing temperature of 820 ℃, pressure of 75MPa and hot pressing time of 18 minutes2S+0.01CuInS2The resultant powder was subjected to rapid hot pressing to obtain a bulk In-doped Cu — S-based thermoelectric material having a nanostructure, shown as Cu of this example In fig. 2(b)2And a section SEM image of a Cu-S-based block sample obtained by S +1 mol% In three-step ball milling and hot pressing.
Example 2:
preparation of Cu by ball milling and radio frequency induction rapid hot pressing in three steps2S +2 mol% In polycrystalline thermoelectric material:
the experimental procedure of example 2 differs from example 1 In that 2 mol% of In raw material was added In step 2).
Example 3:
preparation of Cu by ball milling and radio frequency induction rapid hot pressing in three steps2S +4 mol% In polycrystalline thermoelectric material:
the experimental procedure of example 3 differs from examples 1 and 2 In that 4 mol% of In starting material was added In step 2).
Example 4:
preparation of Cu by ball milling and radio frequency induction rapid hot pressing in three steps2S +4 mol% In polycrystalline thermoelectric material:
the composition, experimental procedure, and other parameters of example 4 were exactly the same as those of example 3, except that the hot pressing temperature in step 4) was 880 ℃.
Example 5:
preparation of Cu by ball milling and radio frequency induction rapid hot pressing in three steps2S +6 mol% In polycrystalline thermoelectric material:
the experimental procedure of example 5 differs from examples 1, 2 and 3 In that 6 mol% of In starting material was added In step 2).
Example 6:
preparation of Cu by ball milling and radio frequency induction rapid hot pressing in three steps2S +6 mol% In polycrystalline thermoelectric material:
the composition, experimental procedure, and other parameters of example 6 were exactly the same as those of example 5, except that the hot pressing temperature in step 4) was 880 ℃.
Comparative example 1:
three-step ball milling and radio frequency induction rapid hot pressing preparation non-dopingMiscellaneous Cu2S polycrystalline thermoelectric material:
the experimental procedure of comparative example 1 is different from example 1 In that no In raw material is added In step 2), as shown In fig. 2(a), showing that this comparative example is undoped Cu2And (3) a section SEM image of a Cu-S base block sample obtained by S three-step ball milling and hot pressing.
Comparative example 2:
one-step ball milling and radio frequency induction rapid hot pressing preparation of Cu2S +1 mol% In polycrystalline thermoelectric material:
the composition of the comparative example 2 is completely the same as that of the example 1, but only one-step ball milling is performed, the ball-material ratio, the rotating speed and other parameters are the same, and the ball milling time is the sum of the ball milling time of the three steps in the example 1.
For the above examples and comparative examples, it can be seen from the schematic diagram in fig. 2 that the microstructure of example 1 is as shown in fig. 2(b), in which a large number of nano second-phase particles having a size of 20 to 100nm are present, and TEM and EDS confirm that it is CuInS2. As shown in FIG. 2(a), it is shown that comparative example 1 is not doped with Cu2And a cross-section SEM image of a Cu-S-based block sample obtained by S three-step ball milling and hot pressing, and the undoped sample of the comparative example 1 does not contain the secondary phase substances.
Referring to FIG. 3, wherein FIG. 3(a) shows Cu prepared by three-step ball milling and hot pressing2The Electrical conductivity (Electrical conductivity) of the S + x mol% In bulk sample, and of the same composition samples prepared In one step, varies with Temperature (Temperature). FIG. 3(b) shows Cu prepared by three-step ball milling and hot pressing2The Power Factor (Power Factor) of S + x mol% In bulk samples, and samples of the same composition prepared by the one-step method, varies with temperature. 3(c) Cu prepared by three-step ball milling and hot pressing2The Thermal conductivity (Thermal conductivity) of the S + x mol% In bulk sample, and the same composition samples prepared In one step, varies with temperature. 3(d) shows Cu prepared by three-step ball milling and hot pressing2The ZT values of S + x mol% In bulk samples and samples of the same composition prepared by one step method vary with temperature.
Wherein x ═ 0 is shown in comparative example 1Undoped Cu2The change in the electrical conductivity of the S polycrystalline thermoelectric material, x ═ 0.01, is shown as Cu in example 12The electrical conductivity of the S +1 mol% In polycrystalline thermoelectric material changed, and x ═ 0.02 was shown for Cu In example 22The electrical conductivity of the S +2 mol% In polycrystalline thermoelectric material changed, x ═ 0.01_ OS, shown as Cu prepared by "one-shot" ball milling and radio frequency induction rapid hot pressing In comparative example 22The electrical conductivity of the S +1 mol% In polycrystalline thermoelectric material was varied, which compares the thermoelectric properties of example 1(x ═ 0.01) and example 2(x ═ 0.02), and comparative example 1(x ═ 0) and comparative example 2 (one-shot x ═ 0.01).
It can be seen that In doping and the three-step method help to improve the electrical conductivity, while at an In molar content of 1%, the material has an ultra-low thermal conductivity while maintaining high electrical properties, and hence ZT is as high as 2.0 at 500 ℃.
In addition, referring to FIG. 4, the thermal conductivity of Cu-S based bulk samples obtained by three-step ball milling and different hot pressing temperatures is shown as a function of temperature in FIG. 4, wherein FIG. 4(a) shows Cu at different temperatures in examples 3 and 42The Thermal conductivity (K) of the S + 4% In polycrystalline thermoelectric material is In a variation relation with the temperature; FIG. 4(b) shows Cu at different temperatures in examples 5 and 62Thermal conductivity (K) of the S + 6% In polycrystalline thermoelectric material varies with temperature. It can be seen that the results show that the thermal conductivity of the thermoelectric material is significantly lower than that of the sample prepared at the hot pressing temperature of 880 deg.c at the hot pressing temperature of 820 deg.c.
In summary, the present invention provides an In-doped Cu-S-based thermoelectric material and a method for preparing the same, the method comprising the following steps: providing a first elementary substance Cu raw material and an elementary substance S raw material, and carrying out first mixing ball milling to obtain a first ball-milled product; adding a simple substance In raw material into the first ball-milled product, and carrying out second mixing ball milling to obtain a second ball-milled product; adding a second simple substance Cu raw material into the second ball-milled product, and carrying out third mixing ball milling to obtain a third ball-milled product; and carrying out hot-pressing sintering on the third ball-milling product by utilizing a radio frequency induction hot-pressing device to obtain the In-doped Cu-S-based thermoelectric material with the nano structure. Through the scheme, the In-doped Cu-S-based thermoelectric material and the preparation method thereof utilize three-step ball milling, and realize the In-situ introduction of the uniformly dispersed nano second phase In the Cu-S-based thermoelectric material by reasonably setting ball milling parameters and doping element content, after the rapid sintering is carried out by utilizing radio frequency induction hot-pressing equipment under proper temperature and pressure, a compact block material is formed, second-phase nano crystal grains which are uniformly dispersed still exist, and has coherent and semi-coherent relation with the matrix, so that the current carriers pass smoothly without influencing the electrical performance, and the phonons are subjected to violent scattering to greatly reduce the thermal conductivity, therefore, the material has excellent thermoelectric performance, and the existence of the second-phase nano grain boundary hinders the long-range diffusion of Cu ions, so that the thermal stability of the material is enhanced. The preparation method is simple in preparation process, easy for mass production and good in controllability. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which may be accomplished by those skilled in the art without departing from the spirit and scope of the present invention as set forth in the appended claims.
Claims (11)
1. An In-doped Cu-S-based thermoelectric material, which is characterized In that the chemical general formula of the Cu-S-based thermoelectric material is 2 x (1-y) Cu2S+yCuInS2Wherein y is more than or equal to 0.002 and less than or equal to 0.10.
2. The In-doped Cu-S based thermoelectric material according to claim 1, wherein y is In a range of 0.005. ltoreq. y.ltoreq.0.03.
3. The In-doped Cu-S-based thermoelectric material of claim 1, wherein the CuInS is2As a second of the Cu-S based thermoelectric materialsPhase of said Cu2S is used as a matrix of the Cu-S based thermoelectric material, wherein the second phase and the matrix have at least one of a coherent relationship and a semi-coherent relationship.
4. A method for preparing an In-doped Cu-S-based thermoelectric material according to any one of claims 1 to 3, comprising the steps of:
providing a first elementary substance Cu raw material and an elementary substance S raw material, and carrying out first mixing ball milling to obtain a first ball-milled product;
adding a simple substance In raw material into the first ball-milled product, and carrying out second mixing ball milling to obtain a second ball-milled product;
adding a second simple substance Cu raw material into the second ball-milled product, and carrying out third mixing ball milling to obtain a third ball-milled product;
and carrying out hot-pressing sintering on the third ball-milling product by utilizing a radio frequency induction hot-pressing device to obtain the In-doped Cu-S-based thermoelectric material with the nano structure.
5. The method of claim 4, wherein the molar ratio of the first elemental Cu material to the elemental S material is between 1:1.9 and 2.1, and the first ball-milled product comprises at least CuS2Wherein, the first mixing ball milling process comprises the following formula of Cu +2S ═ CuS2The reaction is carried out.
6. The method of claim 4 or 5, wherein the molar ratio of the first ball-milled product to the elemental In feedstock comprises 1: y, the second ball-milled product at least comprises CuS2And CuInS2Wherein, the process of carrying out the second mixed ball milling comprises CuS according to a formula2+y In＝(1-y)CuS2+yCuInS2The reaction is carried out.
7. In-doped according to claim 4 or 5 or 6The preparation method of the Cu-S-based thermoelectric material is characterized in that the second simple substance Cu raw material is added according to the components to be designed in corresponding quantity, and the third ball-milling product at least comprises Cu2S and CuInS2Wherein, the third mixing ball milling process comprises CuS according to the formula (1-y)2+y CuInS2+3*(1-y)Cu＝2*(1-y)Cu2S+y CuInS2The reaction is carried out.
8. The method for producing an In-doped Cu-S-based thermoelectric material according to claim 4, 5 or 6, wherein the third ball-milled product has a chemical formula of Cu2-xSInyWherein x is more than or equal to 0 and less than or equal to 0.1.
9. The method according to claim 4, wherein at least one of the first mixing ball mill, the second mixing ball mill and the third mixing ball mill is performed, and further comprising a step of adding a dispersing agent, wherein the dispersing agent comprises n-hexane, the mixing ball mill is performed In a ball-milling tank at a ball-to-material ratio of 12:1-18:1, the rotation speed of the mixing ball mill is 600rpm-1000rpm, and the time of the mixing ball mill is 30min-50 h.
10. The method for preparing the In-doped Cu-S-based thermoelectric material as claimed In claim 4, wherein the power frequency of the RF induction hot-pressing device is greater than or equal to 100kHz, the third ball-milled product is loaded into a high pressure resistant graphite mold, and then hot-pressed for 10min to 55min under the conditions of inert gas protection, the temperature of 650 ℃ to 850 ℃ and the pressure of 35MPa to 95MPa by using the RF induction hot-pressing device, so as to obtain the In-doped Cu-S-based thermoelectric material with the nano structure.
11. The method of claim 10, wherein the inert gas In the rf induction hot-pressing apparatus comprises at least one of nitrogen and argon, and the pressure is 0.08 to 5.5 atm.
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