Room-temperature thermoelectric material Bi < 0.45 > Sb < 0.55 > Te < 1 > Se < 0.05 > and preparation method thereof

Abstract

The invention belongs to the technical field of functional materials for direct conversion of heat energy and electric energy, and particularly discloses a room-temperature thermoelectric material Bi < 0.45 > Sb < 0.55 > Te < 1 > Se < 0.05 > and a preparation method thereof, the molecular formula is Bi < 0.45 > Sb < 0.55 > Te < 1 > Se < 0.05 >, the room-temperature thermoelectric material belongs to a trigonal system, and the space group is P-3m1; on the basis of a BiTe-based material, replacement doping of Sb is carried out, and excessive doping is carried out by using Bi atoms and Se atoms, so that the room-temperature thermoelectric material Bi < 0.45 > Sb < 0.55 > Te < 1 > Se < 0.05 > and an intercalation layer with a [Bi2] layer are obtained, and due to the existence of the intercalation layer, the content of Te is reduced in the process that the material has the performance of the [Bi2Te3] layer, the content of Te is about 43% and is obviously smaller than the content (75%) of Te in Bi2Te3; the ZT value of the room-temperature thermoelectric material at room temperature can reach 0.54, and the material becomes a thermoelectric material with potential commercial value.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials for direct conversion of thermal energy and electrical energy, in particular to a room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 and a preparation method thereof. Background Art

[0002] At present, commercial room temperature thermoelectric materials are all doped with Bi2Te3, with a room temperature thermoelectric figure of merit (ZT) of about 0.8 and an anion-cation molar ratio of about 2:3. The most common is the Bi site Sb atom in Bi2Te3, with a doping concentration of about 75% to form Bi 0.5 Sb 1.5 Te materials, with high Te content, result in high cost of room temperature thermoelectric materials.

[0003] This material contains more Te atoms, which are rare in the earth's crust, and Bi 0.5 Sb 1.5 Take Te as an example. The Te content is about 57%, which will lead to its high price and unsustainable development. In addition, the zone melting synthesis and molding methods commonly used at this stage will cause the sample to have a carrier concentration gradient during the molding process, which will make the performance of different positions of the material different, and the uniformity of the material performance cannot be guaranteed. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a room temperature thermoelectric material Bi based on a new BiTe material. 0.45 Sb 0.55 1E 0.05 and a preparation method thereof.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] One of the purposes of the present invention is to provide a room temperature thermoelectric material Bi based on a novel BiTe material. 0.45 Sb 0.55 1E 0.05 , the molecular formula of the room temperature thermoelectric material is: Bi 0.45 Sb 0.55 1E 0.05 , belongs to the trigonal crystal system, and the space group is P-3m1.

[0007] The second object of the present invention is to provide a room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 The preparation method comprises the following steps:

[0008] S1. Take Bi powder, Sb powder, Te powder and Se powder in a molar ratio of 0.45:0.55:1:0.05, put them in a small quartz tube and mix them evenly, then put the small quartz tube in a large quartz tube;

[0009] S2. Place the large quartz tube in a vacuum system and evacuate it. When the vacuum degree in the vacuum system is less than 10Pa, use a hydrogen-oxygen flame to seal the large quartz tube.

[0010] S3, placing the sealed large quartz tube in a tube furnace and keeping it at 850°C for 24 hours, then directly placing the large quartz tube in water for quenching, and then taking out the sample in the small quartz tube and grinding it;

[0011] S4. Place the ground sample in a small quartz tube and mix it evenly, then place the small quartz tube in a large quartz tube, place the large quartz tube in a vacuum system, and evacuate it. When the vacuum degree in the vacuum system is less than 10Pa, use a hydrogen-oxygen flame to seal the large quartz tube; place the sealed large quartz tube in a tube furnace and anneal it at 475°C for 48 hours, then place the large quartz tube in water for quenching, take out the sample in the small quartz tube and grind it through a 100-mesh sieve;

[0012] S5. The screened sample is subjected to hot pressing to obtain a room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 .

[0013] Preferably, the purity of the Bi powder, Sb powder, Te powder and Se powder is 99.99% or more.

[0014] Preferably, in step S5, the hot pressing process of the hot pressing ingot is: first apply a pressure of 50Mpa, then raise the temperature from room temperature to 450 degrees, keep it warm for 1 hour, finally cool it down naturally to room temperature, and then reduce the pressure to normal pressure.

[0015] Compared with the prior art, the present invention prepares a new room-temperature thermoelectric material BiTe-based material which has a significantly different structure from the Bi2Te3-based thermoelectric material. The BiTe-based material is firstly doped with Sb as a substitution and then overdoped with Bi atoms and Se atoms, thereby obtaining the room-temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 The material has an intercalation layer of [Bi2], and the existence of this intercalation layer reduces the Te content while the material has the performance of the [Bi2Te3] layer. The Te content is about 43%, which is significantly less than the Te content in Bi2Te3 (75%), and can effectively reduce the material cost; the ZT value of the room temperature thermoelectric material at room temperature can reach 0.54, and the material becomes a thermoelectric material with potential commercial value.

[0016] The preparation method of the present invention is simple and controllable. By controlling the reaction process, the particle size of the material can be effectively controlled through screening, the particle size of the material can be improved, and large-scale production can be carried out, thereby maximally avoiding the problem of uneven carrier concentration distribution in the thermoelectric material. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 For the preparation of Bi 0.45 Sb 0.55 1E 0.05 and X-ray diffraction patterns of Bi2Te3.

[0018] Figure 2 For the preparation of Bi 0.45 Sb 0.55 1E 0.05 And the spatial structure diagram of Bi2Te3.

[0019] Figure 3 For the preparation of Bi 0.45 Sb 0.55 1E 0.05 The conductivity test results.

[0020] Figure 4 For the preparation of Bi 0.45 Sb 0.55 1E 0.05 Seebeck coefficient test results.

[0021] Figure 5 For the preparation of Bi 0.45 Sb 0.55 1E 0.05 Thermal conductivity test results.

[0022] Figure 6 For the preparation of Bi 0.45 Sb 0.55 1E 0.05 Thermoelectric figure of merit test results. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the invention.

[0024] Example 1: Room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 Preparation

[0025] Bi powder (purity ≥ 99.99%), Sb powder (purity ≥ 99.99%), Te powder (purity ≥ 99.99%), and Se powder (purity ≥ 99.99%) are taken at a molar ratio of 0.45:0.55:1:0.05, placed in a small quartz tube and mixed evenly, and then the small quartz tube is placed in a large quartz tube; the large quartz tube is placed in a vacuum system and vacuumed, and when the vacuum degree in the vacuum system is less than 10Pa, the large quartz tube is sealed with a hydrogen-oxygen flame; the sealed large quartz tube is placed in a tube furnace and maintained at 850°C for 24 hours. After that, the large quartz tube is directly placed in water for quenching, and then the sample in the small quartz tube is taken out and ground; the ground sample is placed in a small quartz tube and mixed evenly, and then the small quartz tube is placed in a large quartz tube, and the large quartz tube is placed in a vacuum system for vacuuming. When the vacuum degree in the vacuum system is less than 10Pa, the large quartz tube is sealed with a hydrogen-oxygen flame; the sealed large quartz tube is placed in a tube furnace and annealed at 475°C for 48 hours, and then the large quartz tube is placed in water for quenching, and the sample in the small quartz tube is taken out and ground through a 100-mesh sieve to obtain a room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 The sieved samples were cast by hot pressing, first applying a pressure of 50Mpa, then heating from room temperature to 450 degrees, keeping the temperature for 1 hour, and finally cooling naturally to room temperature, and then reducing the pressure to normal pressure, so as to ensure the density of the sample and obtain the ingot-shaped room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 .

[0026] Comparative Example 1: Preparation of traditional thermoelectric material BiTe

[0027] Bi powder (purity ≥ 99.99%) and Te powder (purity ≥ 99.99%) are taken in a molar ratio of 1:1, placed in a small quartz tube and mixed evenly, and then the small quartz tube is placed in a large quartz tube; the large quartz tube is placed in a vacuum system to evacuate, and when the vacuum degree in the vacuum system is less than 10Pa, the large quartz tube is sealed with a hydrogen-oxygen flame; the sealed large quartz tube is placed in a tube furnace and kept at 850°C for 24 hours, and then the large quartz tube is directly placed in water for quenching, and then the sample in the small quartz tube is taken out and ground; the ground sample is placed in a small quartz tube and mixed evenly, and then the small quartz tube is placed in a large quartz tube, and the large quartz tube is placed in a large quartz tube. The quartz tube is placed in a vacuum system for vacuuming. When the vacuum degree in the vacuum system is less than 10Pa, a hydrogen-oxygen flame is used to seal the large quartz tube. The sealed large quartz tube is placed in a tube furnace and annealed at 475°C for 48 hours. The large quartz tube is then quenched in water. The sample in the small quartz tube is taken out and ground through a 100-mesh sieve to obtain the thermoelectric material BiTe. The sieved sample is cast by hot pressing, first applying a pressure of 50Mpa, then heating from room temperature to 450 degrees, keeping warm for 1 hour, and finally naturally cooling to room temperature, and then reducing the pressure to normal pressure. This can ensure the density of the sample and obtain the ingot-shaped thermoelectric material BiTe.

[0028] Comparative Example 2: Preparation of Traditional Thermoelectric Material Bi2Te3

[0029] The reactant element was placed in a quartz tube sealed in a clean container with a cone of about 4 cm in length, placed in a rocking furnace, and melted at 1073K for 10 hours to ensure the uniformity of the initial ingot; then, the initial ingot was placed in a vertical zone melt at 923K, with a growth rate of 8mm / h and a roughly estimated liquid-solid surface temperature gradient of 25K / cm. The regional ingot diameter was 12 mm, and the thermoelectric material Bi2Te3 was obtained. However, this molding will cause the sample to have a carrier concentration gradient, which will make the performance of the material at different locations different, and the uniformity of the material performance cannot be guaranteed.

[0030] The room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 The X-ray powder diffractometer was used to characterize the thermoelectric material BiTe. Figure 1 As shown by Figure 1 It can be seen that Bi 0.45 Sb 0.55 1E 0.05 This is basically consistent with the structure of BiTe, indicating that doping does not change the structure of the material.

[0031] Bi2Te3 has a space group of R-3M, while Bi 0.45 Sb 0.551E 0.05 It belongs to the trigonal crystal system, and its space group is P-3m1; Figure 2 As shown, there is an intercalation of the [Bi2] layer, and the existence of this intercalation reduces the Te content while the material has the performance of the [Bi2Te3] layer, which will significantly reduce the price of the material.

[0032] The ingot-shaped room temperature thermoelectric material Bi is cut by a diamond wire cutting machine. 0.45 Sb 0.55 1E 0.05 Cut into 3mm×3mm×6.5mm cuboid samples and 6mm×6mm×1mm slices, and conduct electrical and thermal performance tests respectively. The specific test process is as follows:

[0033] 1. Test of electrical performance

[0034] The sintered samples were cut into 3mm×3mm×6.5mm block samples for testing, and the conductivity and Seebeck coefficient were tested with ZEM-3. The test was carried out using the four-terminal method. The four electrodes used in the test were connected to the upper and lower electrodes through which current was passed, and two electrodes (side electrodes) for measuring voltage. The rectangular sample was placed vertically between the upper and lower electrodes. The bottom electrode contained a heater, and the four electrodes and the sample were placed in the heating furnace. The measurement process is to first heat the sample to the required temperature using a heating furnace, and then the heating body in the lower electrode starts to heat. After temperature control, there is a certain temperature difference (ΔT) between the upper and lower electrodes. At the same time, two side electrodes are used to measure the potential difference dE between the two contact points, and the Seebeck coefficient is calculated. In the process of measuring conductivity, positive and reverse currents are passed between the upper and lower electrodes, and two test voltage probes measure the voltage between the two contact points, thereby obtaining the resistivity of the sample. In order to protect the electrodes from contamination during the test, boron nitride should be applied to the surface of the sample to prevent the sample from volatilizing. The tested conductivity and Seebeck coefficient are shown in Table 1. Figure 3 , 4. By Figure 3 It can be seen that: with the increase of temperature, the conductivity decreases first and then increases, and the conductivity is the largest at room temperature; Figure 4 It can be seen that the Seebeck coefficient also shows a trend of first decreasing and then increasing, and the Seebeck coefficient is the largest at room temperature.

[0035] 2. Thermal performance test

[0036] A 6mm×6mm×1mm sheet was used to measure the thermal diffusion coefficient of the material using the transient flash method (also known as the laser flash method). The principle of the laser flash method for testing the diffusion coefficient of the material is to place the material in a sample chamber at a certain temperature, and the laser source emits a pulsed laser wave to hit the lower surface of the sample, so that a certain amount of heat is generated on the lower surface and diffuses to the upper surface. The infrared detector above the sample can detect the curve of the sample surface temperature changing with the time, and finally the time required for the sample to half heat up. Then the diffusion coefficient of the sample is obtained from the following formula:

[0037]

[0038] Where: d is the thickness of the sample, t 1 / 2 It refers to the half-heating time.

[0039] The thermal conductivity of the material can be calculated based on the thermal diffusion coefficient using the following formula:

[0040] κ=λC v ρ;

[0041] Where: λ is the thermal diffusion coefficient measured by laser thermal conductivity; Cv is the constant volume specific heat value of the material, calculated using the Dulong-Petit law; ρ is the density of the material.

[0042] Before calculating the material density ρ, it is necessary to use a density balance to test the mass of the sample in air (A), the mass of the sample in ethanol (auxiliary liquid) (B), the density of ethanol P0, the density of air P L (0.0012g / cm 3 ) and the temperature of the measurement environment:

[0043]

[0044] The total thermal conductivity is obtained from Figure 5 ,Depend on Figure 5 It can be seen that: with the increase of temperature, the thermal conductivity tends to increase, and the thermal conductivity is the smallest at room temperature. Low thermal conductivity helps to improve the thermoelectric figure of merit of the material.

[0045] 3. Calculation of thermoelectric figure of merit (ZT)

[0046] Based on the electrical properties (electrical conductivity and Seebeck coefficient) tested above and the thermal properties (thermal conductivity) tested, the thermoelectric figure of merit is calculated mainly using the following formula:

[0047]

[0048] Where: S is the Seebeck coefficient, σ is the conductivity, T is the thermodynamic temperature, K totIt is the total thermal conductivity; the larger the ZT value, the higher the thermoelectric performance and the higher the thermoelectric conversion efficiency of the material.

[0049] Test results such as Figure 6 As shown, the prepared material Bi 0.45 Sb 0.55 1E 0.05 For samples parallel to the pressure direction, the thermoelectric figure of merit ZT can reach 0.54 at 300K.

[0050] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 , characterized in that, The molecular formula of the room temperature thermoelectric material is: Bi 0.47 Sb 0.55 1E 0.05 , belongs to the trigonal crystal system, and the space group is P-3m1.

2. A room temperature thermoelectric material Bi 0.45 Sb 0.55 1E 0.05 The preparation method is characterized in that The following steps are involved: S1. Take Bi powder, Sb powder, Te powder and Se powder in a molar ratio of 0.45:0.55:1:0.05, put them in a small quartz tube and mix them evenly, then put the small quartz tube in a large quartz tube; S2. Place the large quartz tube in a vacuum system and evacuate it. When the vacuum degree in the vacuum system is less than 10Pa, use a hydrogen-oxygen flame to seal the large quartz tube. S3, placing the sealed large quartz tube in a tube furnace and keeping it at 850°C for 24 hours, then directly placing the large quartz tube in water for quenching, and then taking out the sample in the small quartz tube and grinding it; S4. Place the ground sample in a small quartz tube and mix it evenly. Place the small quartz tube in a large quartz tube. Place the large quartz tube in a vacuum system and evacuate it. When the vacuum degree in the vacuum system is less than 10Pa, seal the large quartz tube with a hydrogen-oxygen flame. Place the sealed large quartz tube in a tube furnace and anneal it at 475°C for 48 hours. Place the large quartz tube in water for quenching. Take out the sample in the small quartz tube and grind it through a 100-mesh sieve to obtain the room temperature thermoelectric material Bi. 0.45 Sb 0.55 1E 0.05 .

3. The room temperature thermoelectric material Bi according to claim 2 0.45 Sb 0.55 1E 0.05 The preparation method is characterized in that Also includes: S5. The room temperature thermoelectric material Bi will be obtained 0.45 Sb 0.55 1E 0.05 By hot pressing ingots, ingot-shaped room temperature thermoelectric material Bi is obtained. 0.45 Sb 0.55 1E 0.05 .

4. The room temperature thermoelectric material Bi according to claim 2 0.45 Sb 0.55 1E 0.05 The preparation method is characterized in that: The purity of the Bi powder, Sb powder, Te powder and Se powder is all above 99.99%.

5. The room temperature thermoelectric material Bi according to claim 3 0.45 Sb 0.55 1E 0.05 The preparation method is characterized in that In step S5, the hot pressing process of the hot pressing ingot is: first apply a pressure of 50Mpa, then raise the temperature from room temperature to 450 degrees, keep it warm for 1 hour, finally cool it down to room temperature naturally, and then reduce the pressure to normal pressure.

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