A ternary layered thermoelectric material and its preparation method

Abstract

This invention discloses a ternary layered thermoelectric material and its preparation method, wherein the material is represented by the following chemical formula: Sn 1‑ x Mn x Bi2Te4, 0≤x≤0.3. The preparation method includes: (1) preparing SnTe precursor; (2) preparing MnTe precursor; (3) preparing SnTe using the SnTe precursor obtained in step (1) and the MnTe precursor obtained in step (2). 1‑x Mn x Bi₂Te₄ powder. The Mn-doped SnBi₂Te₄ of this invention can increase the carrier concentration and effective carrier mass of the sample, reduce the Hall mobility, increase the absolute value of the Seebeck coefficient and power factor at low temperatures, and thus improve the dimensionless thermoelectric figure of merit (ZT) at low temperatures, thereby improving the thermoelectric properties of the material. The innovative pre-treatment of cold pressing before annealing allows for more thorough contact between sample particles, promotes solid-state reactions, and improves the purity and crystallinity of the material.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials, and in particular to a ternary layered thermoelectric material and its preparation method. Background Technology

[0002] Today, human demand for energy is skyrocketing, but our conventional energy sources are scarce, leading to increasing attention on unconventional energy sources. Environmental pollution is also a major problem in today's society, so we should actively explore green energy power generation technologies. In various modern industries, most of the energy consumed is dissipated as waste heat. By applying thermoelectric power generation technology, some of this waste heat can be converted into electricity, improving energy utilization efficiency and reducing the use of fossil fuels and greenhouse gas emissions.

[0003] The efficiency of thermoelectric devices largely depends on the dimensionless thermoelectric figure of merit ZT of the material, ZT = S 2 σ / κ, where S is the Seebeck efficiency, σ is the electrical conductivity, and κ is the total thermal conductivity, i.e., the lattice thermal conductivity κ. L and electronic thermal conductivity κ e The sum of these, in semiconductors, is κ. L Bismuth telluride dominates in overall thermal conductivity. Discovered over 50 years ago, it is an excellent thermoelectric material and has been used in room-temperature thermoelectric devices for a long time. However, its performance appears to have reached its maximum limit in recent years, with little improvement. Combining bismuth telluride with other elements to synthesize new ternary compounds is one of the important approaches to developing novel thermoelectric materials.

[0004] SnBi2Te4 is a layered material with a 7-layer module of Te-Bi-Te-Bi-Te as the basic structural unit. It can be synthesized using the traditional solid-state sintering method. The thermoelectric properties of the material can be controlled by doping with other elements. According to previous studies, SnBi2Te4 has a narrow band gap, a suitable Seebeck coefficient, and heavy atoms. Therefore, it is very promising to control its various physical parameters to achieve a high figure of merit (ZT) in thermoelectric performance. Summary of the Invention

[0005] Based on SnBi2Te4 material, Mn doping was performed to synthesize materials with superior thermoelectric properties. A synthesis process with shorter cycle time and higher product quality was explored. This invention provides a ternary layered thermoelectric material and its preparation method.

[0006] The present invention adopts the following technical solution:

[0007] A ternary layered thermoelectric material, the material being represented by the following chemical formula:

[0008] Sn 1-x Mn x Bi2Te4

[0009] Among them, 0 ≤ x ≤ 0.3.

[0010] Further, 0 < x ≤ 0.2 or 0.2 < x ≤ 0.25. For example, x is 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29 or 0.30.

[0011] Further, x = 0, 0.1 or 0.2.

[0012] A method for preparing the material as described in any one of the above, comprising the following steps:

[0013] (1) Prepare a SnTe precursor;

[0014] (2) Prepare a MnTe precursor;

[0015] (3) Use the SnTe precursor prepared in step (1) and the MnTe precursor prepared in step (2) to prepare Sn 1- x Mn x Bi2Te4 powder.

[0016] Further, in step (1), the preparation of the SnTe precursor includes: mixing Sn powder and Te powder together according to the stoichiometric ratio of SnTe under a protective atmosphere, grinding evenly and then loading into a vacuum quartz tube (vacuum degree is 10 -5 -10 - 6 torr), putting the quartz tube into a furnace and keeping it at 830 - 850 °C for 7 - 9 h, and then naturally cooling; taking out the block in the quartz tube and grinding it into powder to obtain the SnTe precursor.

[0017] Further, in step (2), the preparation of the MnTe precursor includes: mixing Mn powder and Te powder together according to the stoichiometric ratio of MnTe under a protective atmosphere, grinding evenly and then loading into a vacuum quartz tube (vacuum degree is 10 -5 -10 - 6 torr), putting the quartz tube into a furnace and keeping it at 950 - 1100 °C for 2.5 - 3.5 d, and then naturally cooling; taking out the block in the quartz tube and grinding it into powder to obtain the MnTe precursor.

[0018] Further, in step (3), the preparation of Sn 1-x Mn x Bi2Te4 powder includes: according to Sn 1-x Mn xThe stoichiometric ratio of Bi₂Te₄ was determined by mixing SnTe precursor, MnTe precursor, and Bi₂Te₃ together under a protective atmosphere, grinding them evenly, and then loading them into a vacuum quartz tube (vacuum degree 10). -5 -10 -6 (torr) The quartz tube is placed in a furnace and held at 850-950℃ for 22-26 hours, then quenched with an ice-water mixture; the quenched block is then removed, ground into powder, pressed into sheets using a cold press, and placed in a vacuum quartz tube (vacuum degree 10). -5 -10 -6 The quartz tube is annealed at 450–550°C for 25–35 days. The block is then removed from the quartz tube and ground into powder to obtain Sn. 1-x Mn x Bi2Te4 (x = 0, 0.1, 0.2) powder.

[0019] Furthermore, the method further includes the following step: (4) taking the Sn synthesized in step (3) 1-x Mn x Bi₂Te₄ powder is hot-pressed. Preferably, the hot pressing includes pressing the ground Sn powder in a vacuum hot press furnace. 1-x Mn x Bi2Te4 powder is pressed into blocks, and the pressure during hot pressing is 65-75 MPa, the temperature is 400-500℃, and the hot pressing time is 20-50 min.

[0020] Specifically, the present invention provides a ternary layered thermoelectric material having the structure shown in chemical formula (1):

[0021] Sn 1-x Mn x Bi2Te4 chemical formula (1)

[0022] Where x = 0, 0.1 or 0.2.

[0023] The method for preparing the material as described above includes the following steps:

[0024] (1) Synthesis of SnTe precursor

[0025] Sn powder (99.99%) and Te powder (99.99%) were mixed together under a protective atmosphere according to the stoichiometric ratio of Sn to Te, ground evenly, and then placed into a vacuum quartz tube (vacuum degree 10). -5 -10 -6 The process involves placing a quartz tube in a box furnace and holding it at 850℃ for 8 hours, then allowing it to cool naturally. The solid material inside the quartz tube is then removed and ground into powder to obtain the SnTe precursor. The temperature regime is summarized below:

[0026]

[0027] (2) Synthesis of MnTe precursor

[0028] Mn powder (99.95%) and Te powder (99.99%) were mixed together under a protective atmosphere according to the stoichiometric ratio of Mn to Te, ground evenly, and then placed into a vacuum quartz tube (vacuum degree 10). -5 -10 -6 The process involves placing a quartz tube in a box furnace and holding it at 1000℃ for 3 days, then allowing it to cool naturally. The solid material inside the quartz tube is then removed and ground into powder to obtain the MnTe precursor. The temperature regime is summarized below:

[0029]

[0030] (3) Synthesis of Sn 1-x Mn x Bi2Te4 (x = 0, 0.1, 0.2) powder

[0031] According to Sn 1-x Mn x The stoichiometric ratio of Bi2Te4 (x = 0, 0.1, 0.2) was determined by mixing SnTe precursor, MnTe precursor, and Bi2Te3 together under a protective atmosphere, grinding them evenly, and then loading them into a vacuum quartz tube (vacuum degree 10). -5 -10 -6 The quartz tube was placed in a hanging furnace and held at 900℃ for 24 hours, then quenched with an ice-water mixture. The quenched block was then removed, ground, and crushed into square sheets of 2g / sheet using a cold press (the cold press pressure was set to 4 tons, and the square hole of the mold used for cold pressing was 1cm × 1cm). These sheets were then placed in a vacuum quartz tube (vacuum degree 10). -5 -10 -6 The quartz tube was annealed at 500℃ for 30 days. The block was then removed from the quartz tube and ground into powder to obtain Sn. 1-x Mn x Bi2Te4 (x = 0, 0.1, 0.2) powder.

[0032] (4) Hot pressing

[0033] Grinded Sn using a vacuum hot press furnace 1-x Mn x Bi2Te4 (x = 0, 0.1, 0.2) powder is pressed into blocks for easy testing. The pressure during hot pressing is 70 MPa, the temperature is 450℃, and the hot pressing time is 30 min.

[0034] (5) Block processing

[0035] The hot-pressed blocks were cut into 3mm×3mm×12mm cubes using a wire EDM machine for Seebeck coefficient measurement.

[0036] The hot-pressed block was cut into small squares of 6mm×6mm×2mm using a wire cutting machine for measuring the thermal diffusivity.

[0037] The hot-pressed block was cut into small squares of 6mm×6mm×0.6mm using a wire EDM machine for measuring carrier concentration and carrier mobility.

[0038] (6) Test

[0039] The hot-pressed Sn was analyzed using a multi-functional rotating target X-ray diffractometer (XRD). 1-x Mn x Phase analysis was performed on the Bi2Te4 sample. High-resolution transmission electron microscopy (Talos F200X), electron probe microanalysis (EPMA-8050G), scanning electron microscopy (SEM), and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used to analyze the hot-pressed Sn. 1-x Mn x The microstructure and elemental distribution of Bi2Te4 (x = 0, 0.1, 0.2) bulk materials were characterized. Due to the extremely low Mn content, conventional X-ray energy dispersive spectroscopy (EDS) could not accurately determine the Mn content; therefore, 5 mg of Sn was used instead. 1-x Mn x Bi₂Te₄ (x = 0, 0.1, 0.2) samples were dissolved in 1 mL of aqua regia, and the Mn content in the aqua regia solution was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). 2+ The concentration of Sn was determined by the thermogravimetric analysis (DSC-TGA) to infer the Mn content in the sample. 1-x Mn x Thermal properties of Bi₂Te₄ (x = 0, 0.1, 0.2) powders. The thermal properties of hot-pressed Sn were tested using a Seebeck coefficient / resistivity analysis system (CTA-3) under helium atmosphere protection. 1-x Mn x The Seebeck coefficient S and electrical conductivity σ of Bi2Te4 (x = 0, 0.1, 0.2) bulk materials were determined. The Seebeck coefficient S and electrical conductivity σ of the hot-pressed Sn were measured using a laser thermal conductivity meter (Netzsch, LFA457). 1-x Mn x Thermal diffusivity of Bi₂Te₄ bulk materials (x = 0, 0.1, 0.2). Specific heat C of the samples. p This was obtained through the Duron-Petit empirical rule. That is:

[0040]

[0041] In the above formula, n is the number of atoms in the chemical formula, R is the thermodynamic constant, which is 8.314 J / (mol·K), and M is the relative molecular mass of the chemical formula.

[0042] The total thermal conductivity of the sample is calculated by the following formula:

[0043] κ=DdC p (3)

[0044] In the formula, κ is the total thermal conductivity, D is the thermal diffusivity, d is the sample density, and C is the total thermal conductivity. p Specific heat.

[0045] The electronic thermal conductivity of the sample is calculated by the following formula.

[0046] κ e =LσT (4)

[0047] In the formula, κ e σ is the electronic thermal conductivity, L is the Lorentz constant, σ is the electrical conductivity, and T is the absolute temperature.

[0048] The carrier concentration and carrier mobility of the sample at room temperature were measured using an AC Hall effect testing system (LakeShore 8400 series).

[0049] Beneficial effects:

[0050] Mn doping of SnBi₂Te₄ can increase the carrier concentration and effective carrier mass of the sample, reduce the Hall mobility, and improve the absolute value of the Seebeck coefficient and power factor at low temperatures, thereby increasing the dimensionless thermoelectric figure of merit (ZT) at low temperatures and improving the thermoelectric properties of the material. Pre-cold pressing of the sample before annealing is innovative, as it allows for more thorough contact between sample particles, promotes solid-state reactions, and improves the purity and crystallinity of the material. Attached Figure Description

[0051] Figure 1 X-ray diffraction patterns of SnTe precursor (a) and MnTe precursor (b);

[0052] Figure 2 Sn after hot pressing 1-x Mn x X-ray diffraction patterns of Bi2Te4 (x = 0, 0.1, 0.2) samples and X-ray diffraction patterns calculated using standard CIF files for SnBi2Te4 and MnBi2Te4;

[0053] Figure 3 Scanning electron microscopy and X-ray energy dispersive spectroscopy of the hot-pressed SnBi2Te4 sample;

[0054] Figure 4 Sn after hot pressing 0.8 Mn 0.2 Scanning electron microscopy and X-ray energy dispersive spectroscopy of Bi2Te4 sample;

[0055] Figure 5 Mn measured by inductively coupled plasma atomic emission spectrometry 2+ A comparison chart of concentrations and theoretical values;

[0056] Figure 6 SnBi2Te4(a) and Sn before hot pressing 0.8 Mn 0.2 DSC-TGA test results of Bi2Te4(b) powder;

[0057] Figure 7 Sn after hot pressing 1-x Mn x The Seebeck coefficient S versus temperature T for Bi2Te4 samples (x=0,0.1,0.2) perpendicular to the hot-pressing direction (a) and parallel to the hot-pressing direction (b);

[0058] Figure 8 Sn after hot pressing 1-x Mn x The relationship between conductivity σ and temperature T for Bi2Te4 samples (x=0,0.1,0.2) perpendicular to the hot-pressing direction (a) and parallel to the hot-pressing direction (b);

[0059] Figure 9 Sn after hot pressing 1-x Mn x The power factor PF versus temperature T for Bi2Te4 samples (x=0,0.1,0.2) perpendicular to the hot-pressing direction (a) and parallel to the hot-pressing direction (b);

[0060] Figure 10 Specific heat C of SnBi2Te4 p A comparison chart of the test results and the results calculated using the Dulong-Petit empirical law;

[0061] Figure 11 Sn after hot pressing 1-x Mn x The thermal conductivity κ of Bi2Te4 (x=0,0.1,0.2) samples versus temperature T in the direction perpendicular to the hot pressing direction (a) and parallel to the hot pressing direction (b);

[0062] Figure 12 Sn after hot pressing 1-x Mn x Electronic thermal conductivity κ of Bi2Te4 samples (x=0,0.1,0.2) perpendicular to the hot-pressing direction (a) and parallel to the hot-pressing direction (b).e Relationship with temperature T;

[0063] Figure 13 Sn after hot pressing 1-x Mn x The lattice thermal conductivity κ of Bi2Te4 (x=0,0.1,0.2) samples perpendicular to the hot-pressing direction (a) and parallel to the hot-pressing direction (b). L Relationship with temperature T;

[0064] Figure 14 Sn after hot pressing 1-x Mn x The dimensionless thermoelectric figure of merit ZT versus temperature T for Bi2Te4 samples (x=0,0.1,0.2) perpendicular to the hot-pressing direction (a) and parallel to the hot-pressing direction (b);

[0065] Figure 15 Sn after hot pressing 1-x Mn x Relationship between carrier concentration (a) and Hall mobility (b) and doping amount for Bi2Te4 (x=0,0.1,0.2) samples;

[0066] Figure 16 Sn at room temperature 1-x Mn x The relationship between the effective electron mass and the Mn doping amount x of Bi2Te4 samples perpendicular and parallel to the hot-pressing direction. Detailed Implementation

[0067] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0068] Example 1

[0069] S1. Grind Sn powder and Te powder in a mortar and pestle in a stoichiometric ratio of 1:1 in an argon-filled glove box until they are evenly mixed and form a uniform powder.

[0070] S2. Transfer the obtained powder to a quartz tube using weighing paper, and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0071] S3. Transfer the sealed quartz tube to a box furnace and heat-treat it at 850℃ for 8 hours, then let it cool naturally.

[0072] S4. Remove the ingot from the quartz tube and grind it into powder using a mortar and pestle to obtain the SnTe precursor.

[0073] The obtained samples were subjected to X-ray diffraction tests, and the results are shown in [reference needed]. Figure 1 (a), Figure 1 (a) is the XRD pattern of the sample obtained in Example 1. It can be seen from the figure that the SnTe precursor has very high purity.

[0074] Example 2

[0075] S1. Grind Mn powder and Te powder in a mortar and pestle in a stoichiometric ratio of 1:1 in an argon-filled glove box until they are evenly mixed and form a uniform powder.

[0076] S2. Transfer the obtained powder to a quartz tube using weighing paper, and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0077] S3. Transfer the sealed quartz tube to a box furnace and heat-treat it at 1000℃ for 3 days, then let it cool naturally.

[0078] S4. Remove the ingot from the quartz tube and grind it into powder using a mortar and pestle to obtain the MnTe precursor.

[0079] Figure 1 (b) is the XRD pattern of the sample obtained in Example 2. It can be seen from the figure that the MnTe precursor contains impurities, but since there is a sintering step later, there is no need to purify the MnTe precursor.

[0080] Example 3

[0081] S1. The SnTe precursor and Bi2Te3 (Aladdin B119271-100g) prepared in Example 1 are ground evenly in a mortar and pestle in a stoichiometric ratio of 1:1 in an argon-filled glove box and mixed together to form a uniform powder.

[0082] S2. Transfer the obtained powder to a quartz tube using weighing paper, and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0083] S3. Place the above quartz tube into a hanging furnace and heat treat it at 900°C for 24 hours, then quench it with an ice-water mixture.

[0084] S4. Remove the quenched ingot from the quartz tube and grind it into powder using a mortar and pestle.

[0085] S5. Press the ground powder into square sheets of 2g / sheet using a cold press (the pressure of the cold press is set to 4 tons, and the square hole of the mold used for cold pressing is 1cm×1cm).

[0086] S6. Transfer the pressed square sheet to a quartz tube and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0087] S7. Transfer the vacuum quartz tube containing the square pieces to a box furnace and heat-treat it at 500°C for 30 days.

[0088] S8. Remove the ingot from the quartz tube and grind it into powder using a mortar and pestle. Hot-press it at 450℃ and 70MPa for 30 minutes to obtain the hot-pressed block material SnBi2Te4.

[0089] Example 4

[0090] S1. The SnTe precursor prepared in Example 1, the MnTe precursor prepared in Example 2, and Bi2Te3 (Aladdin B119271-100g) were ground evenly in a mortar and pestle in a stoichiometric ratio of 9:1:10 to form a uniform powder.

[0091] S2. Transfer the obtained powder to a quartz tube using weighing paper, and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0092] S3. Place the above quartz tube into a hanging furnace and heat treat it at 900°C for 24 hours, then quench it with an ice-water mixture.

[0093] S4. Remove the quenched ingot from the quartz tube and grind it into powder using a mortar and pestle.

[0094] S5. Press the ground powder into square sheets of 2g / sheet using a cold press (the pressure of the cold press is set to 4 tons, and the square hole of the mold used for cold pressing is 1cm×1cm).

[0095] S6. Transfer the pressed square sheet to a quartz tube and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0096] S7. Transfer the vacuum quartz tube containing the square pieces to a box furnace and heat-treat it at 500°C for 30 days.

[0097] S8. Remove the ingot from the quartz tube and grind it into powder using a mortar and pestle. Hot-press at 450℃ and 70MPa for 30 minutes to obtain the hot-pressed block material Sn. 0.9 Mn 0.1 Bi2Te4.

[0098] Example 5

[0099] S1. The SnTe precursor prepared in Example 1, the MnTe precursor prepared in Example 2, and Bi2Te3 (Aladdin B119271-100g) were ground evenly in a mortar and pestle in a stoichiometric ratio of 8:2:10 to form a uniform powder.

[0100] S2. Transfer the obtained powder to a quartz tube using weighing paper, and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0101] S3. Place the above quartz tube into a hanging furnace and heat treat it at 900°C for 24 hours, then quench it with an ice-water mixture.

[0102] S4. Remove the quenched ingot from the quartz tube and grind it into powder using a mortar and pestle.

[0103] S5. Press the ground powder into square sheets of 2g / sheet using a cold press (the pressure of the cold press is set to 4 tons, and the square hole of the mold used for cold pressing is 1cm×1cm).

[0104] S6. Transfer the pressed square sheet to a quartz tube and evacuate the quartz tube to a vacuum level of 10. -5 After torr, seal.

[0105] S7. Transfer the vacuum quartz tube containing the square pieces to a box furnace and heat-treat it at 500°C for 30 days.

[0106] S8. Remove the ingot from the quartz tube and grind it into powder using a mortar and pestle. Hot-press at 450℃ and 70MPa for 30 minutes to obtain the hot-pressed block material Sn. 0.8 Mn 0.2 Bi2Te4.

[0107] Example 6

[0108] (1) Thermoelectric performance testing procedures

[0109] The following tests and calculations were performed on the samples obtained in Examples 2-5:

[0110] Test ①: The hot-pressed block was cut into 3mm×3mm×12mm cubes using a wire EDM machine. These cubes were then placed on a Seebeck measuring instrument (CTA-3). The initial measurement temperature was 20℃, and the second measurement temperature was 50℃. Measurements were then taken at 50℃ intervals up to 400℃. The Seebeck coefficient S and conductivity σ of the block sample were measured as a function of temperature T. The results are shown in [reference 1]. Figure 7 and Figure 8 . Figure 7 The graph shows the Seebeck coefficient S versus temperature T for the samples obtained in Examples 3-5, both perpendicular and parallel to the hot-pressing direction. Figure 8 The graph shows the relationship between the electrical conductivity σ perpendicular to the hot-pressing direction and the temperature T for the samples obtained in Examples 3-5 and the hot-pressing direction.

[0111] Test ②: Using the formula PF=S 2 σ yielded the relationship between the power factor PF of each sample and temperature T; the results are shown in [reference]. Figure 9 . Figure 9 The graph shows the relationship between the power factor PF and temperature T for the samples obtained in Examples 3-5, both perpendicular and parallel to the hot-pressing direction.

[0112] Test ③: The hot-pressed block was cut into small squares of 6mm×6mm×2mm using a wire EDM machine. The thermal diffusivity was measured on a laser thermal conductivity meter. The specific heat C of the sample was also measured. p This was obtained through the Duron-Petit empirical law. In the formula, n is the number of atoms in the chemical formula, R is the thermodynamic constant (8.314 J / (mol·K), and M is the relative molecular mass of the chemical formula. The total thermal conductivity κ of the sample is given by the formula κ=DdC p The formula is calculated to be: where κ is the total thermal conductivity, D is the thermal diffusivity, d is the sample density, and C... p The specific heat is given. From this, the relationship between the thermal conductivity κ of the bulk sample and temperature T can be derived; see the results below. Figure 11 .

[0113] Test 4: Using formula κ e =LσT yields the electronic thermal conductivity κ of each sample. e The relationship between temperature and the equation is given by the formula, where L is the Lorentz constant. (See also...) Figure 12 . Figure 12 The electronic thermal conductivity κ of the samples obtained in Examples 3-5 is perpendicular to the hot-pressing direction and parallel to the hot-pressing direction. e The graph shows the relationship between κ and temperature T. This is derived from the formula κ. L =κ-κ e The lattice thermal conductivity κ of each sample was obtained. L The relationship between temperature changes is shown in the results. Figure 13 . Figure 13 The lattice thermal conductivity κ of the samples obtained in Examples 3-5 is the thermal conductivity perpendicular to and parallel to the hot-pressing direction. L Relationship with temperature T.

[0114] Test 5: Using the formula ZT = S 2 σT / κ yields the dimensionless thermoelectric figure of merit ZT value as a function of temperature for each sample. (See results below.) Figure 14 , Figure 14 The graph shows the relationship between the dimensionless thermoelectric figure of merit ZT and temperature T for the samples obtained in Examples 3-5, both perpendicular and parallel to the hot-pressing direction.

[0115] (2) Characterization results

[0116] X-ray diffraction tests were performed on the samples obtained in Examples 1-2, and the results are shown in [reference needed]. Figure 1 , Figure 1 The images show the XRD patterns of the samples obtained in Examples 1-2. It can be seen that the SnTe precursor has almost no impurities, while the MnTe precursor contains a large amount of MnTe2 phase in addition to the MnTe phase. Since the MnTe precursor will continue to be sintered in the following experiments, it is not necessary to specifically remove the MnTe2 impurity phase in the MnTe precursor.

[0117] X-ray diffraction tests were performed on the samples obtained in Examples 3-5, and the results are shown in [reference needed]. Figure 2 . Figure 2 Sn after hot pressing 1- x Mn x X-ray diffraction patterns of Bi₂Te₄ samples (x = 0, 0.1, 0.2) and X-ray diffraction patterns calculated using standard CIF files for SnBi₂Te₄ and MnBi₂Te₄. The figures show that as the Mn content increases, the peak position shifts to higher angles. According to Bragg's equation 2dsinθ = λ, the lattice constant of the samples gradually decreases. This is because Mn... 2+ Occupied Sn 2+ The position of Mn 2+ The ionic radius (approximately) ) less than Sn 2+ The ionic radius (approximately) ).

[0118] Table 1 Results of Electron Probe Microscopy (EPMA)

[0119]

[0120] Table 2 SnBi2Te4 and Sn after hot pressing 0.8 Mn 0.2 EDS measurements of elemental contents in Bi2Te4 samples

[0121]

[0122] To further characterize the elemental composition and distribution of the sample, the hot-pressed Sn... 1-x Mn x Bi₂Te₄ samples (x = 0, 0.1, 0.2) were subjected to electron probe microanalysis (EPMA) and energy dispersive X-ray spectroscopy (EDS). Table 1 lists the results of electron probe microanalysis (EPMA), and Table 2 lists the results of hot-pressed SnBi₂Te₄ and Sn. 0.8 Mn 0.2EDS measurements of the elemental contents of Bi2Te4 samples.

[0123] X-ray energy dispersive spectroscopy analysis was performed on Examples 3 and 5, and the results are shown in [reference needed]. Figure 3 and Figure 4 . Figure 3 and Figure 4 The images show scanning electron microscopy and X-ray energy dispersive spectroscopy (EDS) images of the samples obtained in Examples 3 and 5. It can be seen that the elemental distribution in the samples obtained in Examples 3 and 5 is very uniform, with no phase separation, and the content of each element is very close to the stoichiometric ratio of the feed ratio of 1:2:4.

[0124] Because the content of Mn is too low, neither electron probe microanalysis (EPMA) nor energy dispersive X-ray spectroscopy (EDS) can accurately measure it. Therefore, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to quantitatively analyze the content of Mn.

[0125] Figure 5 Mn measured by inductively coupled plasma atomic emission spectrometry of the samples obtained in Examples 3-5 2+ The graph compares the concentration of Mn with the theoretical value. It can be seen that the Mn content in the samples obtained in Examples 3-5 is very close to the amount of feed.

[0126] Figure 6 The results are DSC-TGA tests of the samples obtained in Examples 3 and 5. It can be seen that the samples obtained in Examples 3 and 5 begin to lose weight at around 390℃. Heating the samples to 800℃ results in weight losses of 16% and 21%, respectively. At around 595℃, both samples obtained in Examples 3 and 5 exhibit significant endothermic phenomena, indicating that the samples underwent peritectic decomposition at around 595℃, reacting with SnBi₂Te₄ → l + α phase, where l represents the liquid phase and α phase is the SnTe phase with a small amount of Bi₂Te₃ dissolved in it.

[0127] Figure 7 The graphs show the Seebeck coefficient S versus temperature T for the samples obtained in Examples 3-5, perpendicular and parallel to the hot-pressing direction. It can be seen that the sample obtained in Example 3 is n-type conductive, while the samples obtained in Examples 4 and 5 are p-type conductive. For all samples, |S| first increases and then decreases with increasing temperature. In the p-type material, |S| increases with increasing Mn doping concentration.

[0128] Figure 8The graphs show the relationship between the conductivity σ perpendicular and parallel to the hot-pressing direction and temperature T for the samples obtained in Examples 3-5. It can be seen that in the low-temperature range, the conductivity σ perpendicular to the hot-pressing direction decreases with increasing Mn doping concentration, while the conductivity σ parallel to the hot-pressing direction increases with increasing Mn doping concentration. For the same sample, the conductivity perpendicular to the hot-pressing direction is greater than the conductivity parallel to the hot-pressing direction. This may be because SnBi2Te4 has a layered structure, and hot pressing causes the SnBi2Te4 grains to arrange themselves in an orderly manner. The in-plane conductivity of a SnBi2Te4 single crystal is greater than its inter-plane conductivity. In the low-temperature range, the conductivity σ perpendicular to the hot-pressing direction decreases with increasing Mn doping concentration. 2+ It can reduce in-plane conductivity and increase inter-plane conductivity.

[0129] Figure 9 The graphs show the relationship between the power factor PF and temperature T for the samples obtained in Examples 3-5, both perpendicular and parallel to the hot-pressing direction. It can be seen that the power factor of all samples increases with increasing Mn doping concentration in the low-temperature range. Furthermore, as the temperature rises, the power factor first increases and then decreases, with the power factor perpendicular to the hot-pressing direction being smaller than that parallel to the hot-pressing direction. As the doping concentration increases, the temperature at which the power factor reaches its peak shifts towards the higher-temperature region.

[0130] Figure 10 The specific heat C of the sample obtained in Example 3 p The graph compares the test results with those calculated using the Duron-Pertie empirical law. It can be seen that the specific heat C obtained through the two methods... p The values ​​are very close; therefore, the Dulong-Petit empirical law is used to estimate the specific heat C of the sample. p Therefore, the determined total thermal conductivity data is reliable.

[0131] Figure 11 The graphs show the relationship between thermal conductivity κ and temperature T for the samples obtained in Examples 3-5, both perpendicular and parallel to the hot-pressing direction. It can be seen that the thermal conductivity of all samples increases with increasing temperature, and the thermal conductivity perpendicular to the hot-pressing direction is greater than that parallel to the hot-pressing direction. This may be because the SnBi2Te4 crystal layers are bound by van der Waals forces, which are unfavorable for phonon transport.

[0132] Figure 12 The electronic thermal conductivity κ of the samples obtained in Examples 3-5 is perpendicular to the hot-pressing direction and parallel to the hot-pressing direction. e The graph shows the relationship between temperature T and the electronic thermal conductivity. It can be seen that the electronic thermal conductivity of the samples obtained in Examples 3-5 all increases with increasing temperature T, and the electronic thermal conductivity perpendicular to the hot-pressing direction is slightly higher than that parallel to the hot-pressing direction.

[0133] Figure 13The lattice thermal conductivity κ of the samples obtained in Examples 3-5 is the thermal conductivity perpendicular to and parallel to the hot-pressing direction. L The relationship between thermal conductivity and temperature T is shown in the graph. The lattice thermal conductivity of the sample was calculated by subtracting the electronic thermal conductivity from the total thermal conductivity. It can be seen that the lattice thermal conductivity κ of the samples obtained in Examples 3-5 is... L It increases with increasing temperature T.

[0134] Figure 14 The graphs show the relationship between the dimensionless thermoelectric figure of merit (ZT) perpendicular and parallel to the hot-pressing direction and temperature T for the samples obtained in Examples 3-5. It can be seen that the dimensionless thermoelectric figure of merit ZT of the samples obtained in Examples 3-5 first increases and then decreases with increasing temperature. For the samples obtained in Examples 4 and 5, with the increase of Mn doping concentration, the temperature point at which the dimensionless thermoelectric figure of merit ZT reaches its maximum value shifts to the higher temperature region. The dimensionless thermoelectric figure of merit of the Mn-doped samples is significantly improved; within the temperature range of 293.15-673.15 K, the maximum value of the dimensionless thermoelectric figure of merit ZT perpendicular to the hot-pressing direction increases from 0.085 to 0.176.

[0135] Table 3 Sn after hot pressing at room temperature 1-x Mn x Carrier type, carrier concentration, conductivity, and Hall mobility of Bi2Te4 samples (x = 0, 0.1, 0.2)

[0136]

[0137] Table 3 lists the Sn after hot pressing at room temperature. 1-x Mn x Carrier type, carrier concentration n, conductivity σ, and Hall mobility μ of Bi2Te4 samples (x=0,0.1,0.2).

[0138] Figure 15 The graph shows the relationship between carrier concentration and Hall mobility of the samples obtained in Examples 3-5 and the doping amount. It can be seen that as the Mn doping amount increases, the carrier concentration of the samples gradually increases, while the Hall mobility gradually decreases.

[0139] Figure 16 The graph shows the relationship between the effective electron mass and the Mn doping amount x of the samples obtained in Examples 3-5, perpendicular and parallel to the hot-pressing direction. It can be seen that the effective mass of charge carriers in the samples gradually increases with the increase of the Mn doping amount.

[0140] The above embodiments demonstrate that the preparation method provided by the present invention can prepare Sn with good crystallinity and uniform elemental distribution. 1-x Mn xMn doping successfully improved the dimensionless thermoelectric figure of merit ZT of the Bi2Te4 sample, thus enhancing its thermoelectric properties.

[0141] The descriptions of the above embodiments are merely illustrative of the methods and core ideas of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing ternary layered thermoelectric materials, characterized in that, The ternary layered thermoelectric material is represented by the following chemical formula: Sn 1-x Mn x Bi2Te4 Where, 0 < x≤ 0.3; The method includes the following steps: (1) Preparation of SnTe precursor; (2) Preparation of MnTe precursor; (3) Prepare Sn using the SnTe precursor obtained in step (1) and the MnTe precursor obtained in step (2). 1-x Mn x Bi2Te4 powder; In step (1), the preparation of the SnTe precursor includes: mixing Sn powder and Te powder together under a protective atmosphere according to the stoichiometric ratio of SnTe, grinding them evenly, and then loading them into a vacuum quartz tube. The quartz tube is placed in a furnace and kept at 830~850 ℃ for 7~9h, and then cooled naturally. The block in the quartz tube is taken out and ground into powder to obtain the SnTe precursor. In step (2), the preparation of the MnTe precursor includes: mixing Mn powder and Te powder together under a protective atmosphere according to the stoichiometric ratio of MnTe, grinding them evenly, and then loading them into a vacuum quartz tube. The quartz tube is placed in a furnace and kept at 950~1100 ℃ for 2.5~3.5 days, and then cooled naturally. The block in the quartz tube is taken out and ground into powder to obtain the MnTe precursor. In step (3), the preparation of Sn 1-x Mn x Bi2Te4 powder includes: according to Sn 1-x Mn x The stoichiometric ratio of Bi₂Te₄ is determined by mixing SnTe precursor, MnTe precursor, and Bi₂Te₃ together under a protective atmosphere, grinding them evenly, and then loading them into a vacuum quartz tube. The quartz tube is placed in a furnace and held at 850–950 °C for 22–26 h, followed by quenching with an ice-water mixture. The quenched block is then removed, ground into powder, pressed into sheets using a cold press, and placed in a vacuum quartz tube for annealing at 450–550 °C for 25–35 days. The block is then removed from the quartz tube and ground into powder to obtain SnTe₄. 1-x Mn x Bi2Te4 powder.

2. The method according to claim 1, characterized in that, 0.11 x< 0.2 or 0.2< x≤ 0.

25.

3. The method according to claim 1, characterized in that, x= 0.2。 4. The method according to claim 1, characterized in that, The method further includes the following step: (4) taking the Sn obtained in step (3) 1-x Mn x Bi2Te4 powder is hot-pressed.

5. The method according to claim 1, characterized in that, After the quenched block is removed, it is ground and crushed, and then pressed into square pieces of 2 g / piece by a cold press. The pressure of the cold press is set to 3.5~4.5 tons, and the square hole of the mold used for cold pressing is 1 cm×1 cm.

6. The method according to claim 4, characterized in that, The hot pressing includes: using a vacuum hot press furnace to press the ground Sn... 1-x Mn x Bi2Te4 powder is pressed into blocks, and the pressure during hot pressing is 65~75 MPa, the temperature is 400~500℃, and the hot pressing time is 20~50 min.

Images