P-type PbSe-based thermoelectric material and preparation and application thereof

Abstract

The invention belongs to the technical field of energy materials, and particularly relates to a p-type PbSe-based thermoelectric material and preparation and application thereof. The polycrystalline p-type PbSe-based thermoelectric material disclosed by the invention is low in cost, is of a cubic phase structure, has high-room-temperature thermoelectric performance and isotropy, has good mechanical property and is convenient to process; the preparation period is only 18h, the process is simple, the repeatability is good, the consumed time is short, and large-scale use is facilitated; the ZT value of the prepared p-type PbSe-based thermoelectric material at room temperature can reach about 0.6. The invention further provides a full PbSe-based thermoelectric refrigeration device made of the same substrate of the p-type PbSe-based thermoelectric material and the n-type PbSe-based thermoelectric material, and the refrigeration temperature difference can reach 32.8 K when the hot end is 300K; the compatibility problem of the thermoelectric device is reduced, the cost performance of the thermoelectric device is improved, and the thermoelectric refrigeration device is expected to realize large-scale application in the field of near-room-temperature thermoelectric refrigeration.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy materials, and specifically relates to a p-type PbSe-based thermoelectric material and a preparation and application thereof. Background Art

[0002] Thermoelectric energy conversion technology is a green and pollution-free energy conversion technology. Thermoelectric materials can realize the direct conversion between thermal energy and electrical energy, and can be used for cooling by using the Peltier effect. Thermoelectric cooling devices are made of n-type and p-type thermoelectric arms in electrical series and thermal parallel. Thermoelectric cooling technology has the advantages of high efficiency, environmental protection, and reliability. At present, it has been widely used in the fields of temperature control of electronic components, cooling of optoelectronic devices, sample refrigeration in the biomedical field, laser treatment, etc., and micro-refrigeration systems.

[0003] As the only thermoelectric refrigeration material that has been commercialized so far, bismuth telluride is a typical layered compound with interlayer interactions by van der Waals forces. In addition, bismuth telluride has anisotropy in thermoelectric properties and has better thermoelectric properties in the intralayer direction. Therefore, improving the orientation of bismuth telluride materials is one of the methods to obtain better thermoelectric properties. In actual large-scale production, the process of zone melting directional growth is generally used to prepare bismuth telluride materials. However, since the directional growth material is easy to cleave along the growth direction, the mechanical strength is low and the crystal preparation cycle is long. In addition, bismuth telluride-based materials are not conducive to long-term large-scale applications because they contain expensive and scarce Te elements. Therefore, the development of new thermoelectric materials with low cost, high mechanical properties and excellent thermoelectric properties at near room temperature is an urgent problem to be solved. Summary of the invention

[0004] In view of the above-mentioned problems or shortcomings, in order to solve the problems of high cost and low mechanical strength of the existing commercial thermoelectric material bismuth telluride, the present invention provides a p-type PbSe-based thermoelectric material and its preparation and application. The prepared p-type PbSe (lead selenide)-based thermoelectric material does not contain Te element, and only uses low-cost Cu element doping to obtain a material with a room temperature ZT value of up to 0.6, which has both low cost and high performance; and further provides a thermoelectric refrigeration device based on the p-type PbSe (lead selenide)-based thermoelectric material. Compared with the thermoelectric refrigeration device constructed using bismuth telluride thermoelectric material with a layered structure, the full PbSe-based thermoelectric refrigeration device constructed using n-type and p-type PbSe-based thermoelectric materials with a cubic phase structure in the present invention has stronger mechanical properties and long-term service stability.

[0005] The specific technical solutions of the present invention are as follows:

[0006] In the first aspect, a p-type PbSe-based thermoelectric material having a chemical formula of Pb (1-x)-y Cu ySe; wherein 0.005≤x≤0.03, 0<y≤0.006, which has low cost and excellent performance; PbSe is obtained by using Pb vacancy doping 1-x Se, which transforms PbSe into a hole-dominated p-type electrical transport; then in the Se-rich Pb 1-x Se, using Cu to replace Pb to regulate its hole carrier concentration to obtain Pb (1-x)-y Cu y Se.

[0007] As the temperature of intrinsic PbSe changes, the p-type electrical transport behavior dominated by hole carriers will change to the n-type electrical transport behavior dominated by electrons, that is, p→n transition. Therefore, the present invention first adopts Pb vacancy doping in PbSe, that is, Pb 1-x Se, which transforms PbSe into a strong p-type electrical transport behavior dominated by holes.

[0008] It is well known that the thermoelectric parameters of thermoelectric materials are closely related to the carrier concentration. 1- x Se, Cu is used to replace Pb to further fine-tune its hole carrier concentration, that is, Pb (1-x)-y Cu y Se. The reasons for choosing Cu to optimize p-type PbSe are as follows: 1) The p-type dopants commonly used in PbSe, such as Na, K, and Ag, have high doping efficiency, and require very small doping amounts to finely control the carrier concentration. The weighing process is difficult to operate and has large errors; 2) The interstitial formation energy of Cu in Se-rich PbSe (Cu i ) is the lowest, followed by Cu replacing Pb (Cu Pb ) formation energy. Cu ion (Cu + ) is +1, Cu i It means that Cu enters the lattice gap of PbSe and becomes Cu + Release electrons to the substrate, reducing the hole carrier concentration. Pb It means that Cu occupies the Pb position of the PbSe lattice, increasing the hole carrier concentration. i and Cu Pb The formation energy is close, so the present invention uses Cu in Pb 1-x Cu in Se (Se-rich) i and Cu Pb The competitive relationship between the two makes it easier to finely control the hole carrier concentration of p-type PbSe.

[0009] Preferably, x=0.01.

[0010] Preferably, 0.001≤y≤0.002.

[0011] Preferably, the p-type PbSe-based thermoelectric material is Pb 0.988 Cu 0.002 Se.

[0012] In a second aspect, the method for preparing the above-mentioned p-type PbSe-based thermoelectric material comprises the following steps:

[0013] Step 1: Pb and Se with elemental purity independently greater than 99.999% and Cu with purity greater than 99.99% are used according to Pb (1-x)-y Cu y Weigh the raw materials and prepare the materials according to the atomic stoichiometric ratio of Se.

[0014] Step 2: Place the raw materials prepared in step 1 under a vacuum of less than 10 -3 Pa vacuum environment, and then keep it in a high temperature environment of 1050±50℃ for more than 6h for melting reaction, and then cool it to room temperature with the furnace to obtain polycrystalline p-type PbSe-based thermoelectric material.

[0015] Preferably, the temperature control program of the high temperature environment is: heating to 1050±50°C within 10-24 hours and keeping the temperature for more than 6 hours.

[0016] Thirdly, the application of the above-mentioned p-type PbSe-based thermoelectric material: firstly, the p-type PbSe-based thermoelectric material is made into powder, which is then put into a mold for vacuum hot pressing and sintering to form a thermoelectric arm; the n-type PbSe-based thermoelectric material is also made into a thermoelectric arm. Then, the two thermoelectric arms are connected in series electrically and in parallel thermally to form a full PbSe-based thermoelectric device.

[0017] Preferably, the vacuum hot pressing sintering process is specifically carried out at a pressure of 40-50 MPa and a temperature of 500±50° C. for at least 5 minutes.

[0018] Preferably, the p-type PbSe-based thermoelectric material Pb 0.988 Cu 0.002 Se and n-type PbSe-based thermoelectric materials Pb 1.02 Se-0.2%Cu are used to make thermoelectric arms respectively, and the two types of thermoelectric arms are connected in series in a group, one each, to form a full PbSe-based thermoelectric device.

[0019] The devices reported so far using PbSe-based thermoelectric materials are all made with commercial Bi 2 Te 3 Thermoelectric materials, and most of the PbSe-based thermoelectric materials are single crystal materials; but PbSe crystal / commercial Bi 2 Te 3The cost performance ratio of the device is low, and the growth and preparation cycle of single crystal materials is generally long. The present invention provides for the first time a p-type Pb (1-x)-y Cu y Se (such as Pb 0.988 Cu 0.002 Se) and n-type PbSe-based thermoelectric materials (such as Pb 1.02 The all-PbSe-based thermoelectric device made of Te-free PbSe thermoelectric material has the following beneficial effects: 1) both the n-type and p-type thermoelectric arms use the same kind of matrix thermoelectric material, which can reduce the compatibility problems of thermoelectric devices; 2) the preparation cycle of polycrystalline thermoelectric materials is short, and the mechanical properties are good and the production cost is low; 3) both the n-type and p-type thermoelectric arms are made of Te-free PbSe thermoelectric material, which reduces the raw material consumption cost of the material and improves the cost performance of thermoelectric devices.

[0020] In summary, the present invention uses low-cost Pb, Se and Cu elements as raw materials to prepare p-type PbSe-based thermoelectric materials with high room temperature thermoelectric performance, which is better than existing commercial thermoelectric materials (such as Bi 2 Te 3 The p-type PbSe-based thermoelectric material has a cubic phase structure and isotropic, which is better than the Bi-type PbSe-based thermoelectric material with a layered crystal structure and easy cleavage along the interlayer. 2 Te 3 The PbSe-based thermoelectric material has better mechanical properties and is easy to process. Compared with the several days to several weeks required for single crystal growth, the preparation of polycrystalline PbSe-based thermoelectric materials only takes 18 hours. The preparation process is simple, reproducible, and time-saving, which is conducive to long-term large-scale use. The ZT value of the prepared p-type PbSe-based thermoelectric material at room temperature can reach about 0.6. It further provides a thermoelectric cooling device made of the same matrix of p-type PbSe-based thermoelectric material and n-type PbSe-based thermoelectric material, and the cooling temperature difference can reach 32.8K when the hot end is 300K; it reduces the compatibility problem of thermoelectric devices and improves the cost performance of thermoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 for Bi 2 Te 3 and PbSe, the crystal structure and mechanical strength, and the crustal abundance and production of the elements involved;

[0022] Figure 2 It is a schematic diagram of the structure of the high temperature melting furnace and the vacuum rapid hot pressing furnace used in the embodiment;

[0023] Figure 3 The thermoelectric performance of the samples of Examples 1-3 is measured;

[0024] Figure 4 The relationship between the ZT value and the hole carrier concentration p of the p-type PbSe sample in the embodiment;

[0025] Figure 5 This is a diagram showing the cooling temperature difference performance of the all-PbSe-based thermoelectric device in the embodiment;

[0026] Figure 6 4 is a comparison chart of the refrigeration temperature difference performance of the thermoelectric devices in the embodiments. DETAILED DESCRIPTION

[0027] The technical scheme and advantages of the present invention will be further described in detail below by combining the accompanying drawings with the embodiments. The technical scheme of the present invention is not limited to the specific implementation modes listed below, and the embodiments are only used to explain the present invention.

[0028] Figure 1 for Bi 2 Te 3 and PbSe, as well as the crustal abundance and production of the elements involved. 2 Te 3 and the crystal structure of PbSe, it can be seen that Bi 2 Te 3 (b) is the crystal structure of PbSe used in the present invention. It can be seen that PbSe is a cubic phase crystal structure and isotropic. (c) is the prepared single crystal or polycrystalline Bi 2 Te 3 The Young's modulus of PbSe and PbSe shows that PbSe has a higher Young's modulus and therefore has stronger mechanical properties. (d) is a commercial n-type Bi 2 (Te, Se) 3 , p type (Bi, Sb) 2 Te 3 Compared with the crustal abundance and output of the elements used in PbSe, it can be seen that the elements used in PbSe-based thermoelectric materials have high crustal abundance, so the manufacturing cost is lower.

[0029] Example

[0030] A method for preparing a p-type PbSe-based thermoelectric material comprises the following steps:

[0031] Step 1: Pb blocks, Se particles and Cu wires with purity greater than 99.999% are prepared according to the Pb (1-x)-y Cu y The raw materials are weighed and prepared according to the atomic stoichiometric ratio of Se. In the embodiment, taking x=0.01 as an example, Pb 0.99-y Cu ySe; take y=0.001, 0.0015, 0.002 as the corresponding embodiments 1-3 respectively.

[0032] Step 2: Place the mixed raw materials weighed in step 1 into a round-bottomed quartz tube (with an inner diameter of 17 mm and an outer diameter of 20 mm), and then evacuate the quartz tube to a vacuum degree of less than 10 -3 Pa, seal the quartz tube with flame;

[0033] Then the sealed quartz tube is inserted into a fire brick with a hole, and then placed in a high-temperature furnace. The temperature control program of the high-temperature furnace is set as follows: heating to 1050°C in 12 hours, keeping the temperature for 6 hours, and then cooling to room temperature to obtain a polycrystalline p-type PbSe-based thermoelectric material ingot sample.

[0034] Step 3: Grind the p-type PbSe-based thermoelectric material ingot sample obtained in step 2 into powder using an agate mortar, insert a layer of carbon paper into a graphite mold, and then put it into a graphite mold for vacuum hot pressing and sintering. The diameter of the graphite mold is 15 mm.

[0035] The pressure and temperature control program of the vacuum hot press furnace is: pressure 50MPa (883Kg), pressure holding for 35min. First increase the pressure to 50MPa, start the temperature program after 10min, heat to 500℃ in 500s, keep warm for 20min, after the end of the heat preservation, the sample is cooled to room temperature with the furnace, and a dense disc sample with a diameter of 15mm is obtained. The height is related to the mass of the added powder. The heat preservation time must be set to be at least 1min greater than the remaining pressure holding time when the temperature program is started.

[0036] After the carbon paper is removed from the disc-shaped sample obtained by hot pressing, the sample is cut using a low-speed cutting machine, and then sanded using sandpaper to form the columnar and sheet samples required for testing electrical and thermal properties. The length and width of the columnar sample does not exceed 5 mm, and the height is between 10-15 mm; the sheet sample has a thickness of 1-2 mm and can be square or round, depending on the size of the sample support. In this embodiment, a sample support of 8mm*8mm, 6mm*6mm or φ6mm is selected, and then the thermoelectric performance of the sample is tested.

[0037] Step 4: Preparation of all-PbSe-based thermoelectric cooling devices:

[0038] The p-type Pb with the best room temperature thermoelectric performance prepared in step 3 0.988 Cu 0.002 Se samples and n-type Pb 1.02 Se-0.2%Cu sample (self-prepared) was cut and polished into 3mm*3mm*5mm rectangular columns, which were used as n-type and p-type thermoelectric arms of the thermoelectric cooling device. Seven pairs of n-type and p-type thermoelectric arms were used to construct the thermoelectric device in the form of electrical series connection and thermal parallel connection. The solder was Sn 42Bi 58 Lead-free solder, soldering temperature is 178°C. Solder two wires.

[0039] Figure 2 The schematic diagrams of the high-temperature melting furnace and vacuum rapid hot pressing sintering furnace used in the examples are shown in Figure 1. (a) is a schematic diagram of the high-temperature furnace, where the raw material or sample is placed in a round-bottomed quartz tube, which is nearly vertically placed in a perforated fire brick, and a melting reaction can be performed according to the temperature control program. (b) is a schematic diagram of the vacuum rapid hot pressing sintering furnace, where the powder sample is placed in a graphite mold and hot pressed and sintered in a vacuum environment.

[0040] The Seebeck and resistivity test system and the laser thermal conductivity meter were used to test the thermoelectric properties of the samples of Examples 1-3, including: electrical conductivity σ, Seebeck coefficient S and thermal diffusion coefficient D (given by the formula κ tot =ρC p D is calculated to obtain the total thermal conductivity), and the result is as follows Figure 3 The test temperature range of the material is from room temperature to 300°C (573K).

[0041] Figure 3 Thermoelectric performance test results of Examples 1-3 are as follows:

[0042] (a) is the temperature-dependent conductivity σ, (b) is the temperature-dependent Seebeck coefficient S, (c) is the temperature-dependent power factor PF, and (d) is the temperature-dependent total thermal conductivity κ tot , (e) is the lattice thermal conductivity κ that varies with temperature lat , (f) is the dimensionless thermoelectric figure of merit ZT value that varies with temperature. 0.988 Cu 0.002 The room temperature ZT value of Se is 0.6.

[0043] Figure 4 The relationship between the ZT value and the hole carrier concentration p of the p-type PbSe sample in the embodiment. By statistically analyzing the p-type PbSe in which only copper (Cu), silver (Ag), sodium (Na) and potassium (K) are used for substitutional doping at the Pb position in PbSe at room temperature (300K) and the p-type PbSe in which Pb vacancies and Cu are used to replace Pb positions in PbSe in the present invention, it can be seen that the hole carrier concentration p of the p-type PbSe with a higher room temperature ZT value should be within 10 18 -10 19 cm -3 The doping efficiency of Ag, Na and K is relatively high, which can easily make the hole carrier concentration exceed the optimal range. i ) formation energy and substitution of Pb(Cu Pb) have low formation energies, so Cu has the property of being mobile in p-type PbSe, that is, it will move between the interstitial position and the Pb position. The two defects compete with each other, so the obtained hole carrier concentration is lower than the optimal range. i It will release electrons from PbSe, reduce the hole carrier concentration, and form Cu Pb This will generate holes in PbSe.

[0044] For the previously reported Pb 1-x Cu x Se series, in intrinsic PbSe (intrinsic PbSe contains a small amount of vacancies, and exhibits p-type hole transport at room temperature, but as the temperature rises, the p-type electrical transport behavior dominated by hole carriers will change to n-type electrical transport behavior dominated by electrons, that is, p→n transition), directly using Cu to replace Pb position for doping, the resulting hole carrier concentration is low, so the obtained ZT value still has room for improvement. In the present invention, a certain amount of Pb is first introduced into PbSe, and then Cu is used to replace Pb doping, and the resulting Pb (1-x)-y Cu y Se series, all obtained higher room temperature ZT values; among them, Pb 0.988 Cu 0.002 The room temperature ZT value of the Se component can reach 0.6. Therefore, the present invention utilizes the synergistic effect of Pb vacancies and mobile Cu atoms to obtain a p-type PbSe thermoelectric material with a higher room temperature ZT value.

[0045] Figure 5 The refrigeration temperature difference performance diagram of the all-PbSe based thermoelectric device in the embodiment. The thermoelectric device consists of 7 pairs of p-type Pb 0.988 Cu 0.002 Se and n-type Pb 1.02 Se-0.2%Cu. The upper left corner of the figure shows the ZT values ​​of n-type and p-type PbSe used in the device of the present invention in the near room temperature range (300-573K) and the lower right corner shows 7 pairs of all-PbSe-based thermoelectric devices in the embodiment of the present invention. When the hot end of the thermoelectric cooling device is maintained at 303K, 323K and 343K respectively, the cooling temperature difference (ΔT C ) can reach 32.8K, 36.9K and 41.0K respectively.

[0046] Figure 6 The refrigeration temperature difference performance comparison diagram of the thermoelectric device in the embodiment. Among them, (a) is the full PbSe-based thermoelectric refrigeration device and PbSnS 2 / (Bi,Sb) 2 Te 3The cooling temperature difference of the thermoelectric device. The upper left corner is embedded with 7 pairs of all-PbSe-based thermoelectric devices of the present invention. It can be seen from the figure that the all-PbSe-based thermoelectric cooling device prepared by the present invention is better than that containing (Bi, Sb) 2 Te 3 The cooling device of the thermoelectric arm has a better cooling temperature difference. (b) is the p-type Pb used in the present invention. 0.988 Cu 0.002 The thermoelectric performance of the Se samples and other high-performance PbSe-based thermoelectric materials at near room temperature is compared, including the n-type PbSe used in the present invention. 1.02 Thermoelectric properties of Se-0.2%Cu sample (self-prepared). As shown in the figure, the p-type Pb 0.988 Cu 0.002 Se samples have excellent near-room temperature thermoelectric properties, and therefore have better near-room temperature cooling performance. (c) PbSe-based and Bi 2 Te 3 The cooling temperature difference performance and price ratio of the PbSe-based thermoelectric cooling device at the hot end of 300K (the denominator is the weighted price of Se and Te used in the n-type and p-type thermoelectric arms of the device), as well as the abundance of Se and Te. As can be seen from the figure, the all-PbSe-based thermoelectric cooling device is better than Bi 2 Te 3 Thermoelectric cooling devices have a higher cost performance.

[0047] It can be seen from the above embodiments that the polycrystalline p-type PbSe-based thermoelectric material of the present invention has low cost, cubic phase structure, high room temperature thermoelectric performance, isotropy, good mechanical properties, and is easy to process; the preparation cycle only takes 18 hours, the process is simple, the repeatability is good, the time consumption is short, and it is conducive to large-scale use; the ZT value of the prepared p-type PbSe-based thermoelectric material at room temperature can reach about 0.6. And further provides a thermoelectric refrigeration device made of the same matrix of p-type PbSe-based thermoelectric material and n-type PbSe-based thermoelectric material, the cooling temperature difference can reach 32.8K when the hot end is 300K; reduce the compatibility problem of thermoelectric devices, improve the cost performance of thermoelectric devices, so that thermoelectric refrigeration devices are expected to be widely used in the field of near-room temperature thermoelectric refrigeration.

Claims

1. A p-type PbSe-based thermoelectric material, characterized in that: The chemical formula is Pb (1-x)-y Cu y Se; wherein 0.005≤x≤0.03, 0<y≤0.006; Pb is obtained by doping Pb vacancies in PbSe 1-x Se, which transforms PbSe into a hole-dominated p-type electrical transport; then in the Se-rich Pb 1-x Se, using Cu to replace Pb to regulate its hole carrier concentration to obtain Pb (1-x)-y Cu y Se.

2. The p-type PbSe-based thermoelectric material according to claim 1, characterized in that: Said x=0.

01.

3. The p-type PbSe-based thermoelectric material according to claim 1, characterized in that: The 0.001≤y≤0.

002.

4. The p-type PbSe-based thermoelectric material according to claim 1, characterized in that: The p-type all-PbSe-based thermoelectric material is Pb 0.988 Cu 0.002 Se.

5. The method for preparing a p-type PbSe-based thermoelectric material according to claim 1, characterized in that: The following steps are involved: Step 1: Pb and Se with elemental purity independently greater than 99.999% and Cu with purity greater than 99.99% are used according to Pb (1-x)-y Cu y Weigh the raw materials according to the atomic stoichiometric ratio of Se and prepare the materials; Step 2: Place the raw materials prepared in step 1 under a vacuum of less than 10 -3 Pa vacuum environment, and then keep it in a high temperature environment of 1050±50℃ for more than 6h for melting reaction, and then cool it to room temperature with the furnace to obtain polycrystalline p-type PbSe-based thermoelectric material.

6. The method for preparing a p-type PbSe-based thermoelectric material according to claim 5, characterized in that: The temperature control program of the high temperature environment is to increase the temperature to 1050±50°C within 10-24h.

7. The use of the p-type PbSe-based thermoelectric material according to claim 1, characterized in that: First, the p-type PbSe-based thermoelectric material is made into powder, which is then put into a mold and subjected to vacuum hot pressing and sintering to form a thermoelectric arm; the n-type PbSe-based thermoelectric material is also made into a thermoelectric arm; The two thermoelectric arms are then connected in electrical series and thermally in parallel to form a fully PbSe-based thermoelectric device.

8. The use of the p-type PbSe-based thermoelectric material according to claim 7, characterized in that: The vacuum hot pressing sintering process is specifically to maintain the pressure at 40-50 MPa and the temperature at 500±50° C. for at least 5 minutes.

9. The use of the p-type PbSe-based thermoelectric material according to claim 7, characterized in that: The p-type PbSe-based thermoelectric material Pb 0.988 Cu 0.002 Se and n-type PbSe-based thermoelectric materials Pb 1.02 Se-0.2%Cu are used to make thermoelectric arms respectively, and the two types of thermoelectric arms are connected in series in a group, one each, to form a full PbSe-based thermoelectric device.

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