N-type bismuth telluride single crystal thermoelectric material and batch production method thereof

Abstract

The application discloses an N-type bismuth telluride single crystal thermoelectric material and a batch preparation method thereof. (3‑x) Se x +y%wtAgI, x=0.3 or 0.5, and corresponding y=0.11 or 0.10; the proportion of Se is adjusted by x to expand the band gap; the doping amount of AgI is adjusted by y to control the carrier concentration, and the overall performance of the material is further improved. Through double-temperature-zone growth, the application precisely establishes a temperature gradient effect, forms a high-quality single crystal, effectively improves the carrier mobility, and reduces the influence of the bipolar effect. Meanwhile, the prepared material has good uniformity, excellent thermoelectric performance, large single-tube yield, and is suitable for batch preparation.

Description

Technical Field

[0001] This invention belongs to the field of new energy material preparation technology, specifically relating to an N-type bismuth telluride single crystal thermoelectric material and its mass production method. Background Technology

[0002] Currently, considering the global energy utilization and development, primary energy sources such as oil and coal are becoming increasingly depleted. At the same time, the extensive use of fossil fuels has led to increasingly serious environmental pollution problems. Therefore, research on new energy sources and their conversion materials is receiving increasing attention. Thermoelectric materials (also known as thermoelectric power generation materials) are semiconductor functional materials that utilize the repeated cyclical movement of charge carriers within a solid to achieve the mutual conversion between thermal energy and electrical energy. They possess advantages such as small size, long service life, no noise, and environmental friendliness, and have broad application value and prospects in waste heat recovery and refrigeration fields, perfectly meeting the requirements of the new energy field and becoming one of the current research hotspots.

[0003] Bismuth telluride thermoelectric materials stand out among thermoelectric materials in the low-temperature range (room temperature to 300°C) due to their high power factor and low thermal conductivity. They are currently the only commercially available thermoelectric material on a large scale and have achieved relatively mature industrialization. Since the performance of thermoelectric materials directly affects the effectiveness of thermoelectric power generation and thermoelectric cooling devices, there is an urgent need to optimize the performance of bismuth telluride thermoelectric materials.

[0004] Typically, the performance of thermoelectric materials can be measured using the dimensionless thermoelectric figure of merit ZT (ZT=S). 2 The formula is σT / κ, where S represents the Seebeck coefficient, σ represents electrical conductivity, T represents absolute temperature, and κ represents thermal conductivity. As the ZT value increases, the performance of the thermoelectric material also improves. Therefore, as shown in the formula, the material's performance mainly depends on the electrical conductivity σ, the Seebeck coefficient S, and the thermal conductivity κ. To obtain bismuth telluride thermoelectric materials with high thermoelectric figures of merit, the coupling relationship between these three parameters must be improved; that is, high-performance thermoelectric materials need to maintain low thermal conductivity while satisfying high Seebeck coefficient and electrical conductivity.

[0005] Previous studies have shown that bismuth telluride thermoelectric materials can achieve high thermoelectric performance through doping with elements such as Gb, Ce, and Sn. In particular, using Sb as a donor, its electrical transport properties can be optimized to enhance the thermoelectric performance of Bi. 2-x Sb x Te3 exhibits a significantly improved ZT value and is considered the most suitable p-type thermoelectric material for use near room temperature. However, currently industrially produced bismuth telluride thermoelectric materials have a room temperature ZT value of only 1 due to their high thermal conductivity. In particular, the ZT value of N-type thermoelectric materials is generally lower than that of P-type thermoelectric materials, and they also have significant defects, such as high thermal conductivity, low carrier mobility, and bipolar effects that affect the material's ZT value.

[0006] The patent with the publication number CN115196965B discloses an n-type bismuth telluride thermoelectric material composed of Bi2Te 3-x Se x +y%SbI3 (x < 0.5, 0 < y < 0.3) and its preparation method. The preparation method includes the following steps: First, ball-mill and mechanically alloy the component materials according to the stoichiometric ratio; then, perform stepwise hot-press sintering on the ball-milled materials. The n-type bismuth telluride thermoelectric material obtained by this method has a stable and moderate carrier concentration, and both the mechanical strength and thermoelectric performance can meet the preparation requirements of micro thermoelectric refrigeration devices.

[0007] Currently, in the preparation process of bismuth telluride thermoelectric materials, the ball-mill hot-press sintering method is a commonly used method. However, this method has some problems and defects, mainly including the following aspects:

[0008] 1. During the ball-milling process, due to the presence of high temperature and oxygen, the material is prone to oxidation reactions; due to the wear of the grinding balls and containers, metal impurities are introduced, resulting in a decrease in thermoelectric performance.

[0009] 2. During the ball-milling process, a long ball-milling time is required to obtain a fine particle size, which increases the time and energy consumption of the preparation process.

[0010] 3. During the sintering process, due to the uneven temperature during the heating and cooling processes, the prepared material is prone to non-uniform performance between the outside and inside of the sintered block, reducing the thermoelectric performance of the material.

[0011] 4. During the ball-milling and hot-press sintering processes, due to the high process complexity and large operation difficulty, the production efficiency is low and the output is limited.

[0012] In view of the above reasons and defects, it is urgent to develop an N-type bismuth telluride single crystal thermoelectric material with excellent thermoelectric performance, high commercialization degree and capable of batch preparation. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide an N-type bismuth telluride single crystal thermoelectric material and its batch preparation method in view of the deficiencies of the above-mentioned prior art. High-purity raw materials are used to reduce the introduction of impurities, the crushing and re-encapsulation process is combined to improve the uniformity of the material, the influence of the bipolar effect is reduced by increasing the proportion of wide-bandgap elements, and the temperature gradient single crystal growth method (dual-temperature zone growth technology) is used for preparation to improve the material orientation and carrier mobility. No manual intervention is required during the single crystal growth process, and multiple devices can be produced simultaneously. The prepared material has good uniformity, excellent thermoelectric performance, a large single-tube output, and is suitable for batch preparation.

[0014] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0015] A type N-type bismuth telluride single-crystal thermoelectric material, wherein the N-type bismuth telluride single-crystal thermoelectric material is prepared by dual-temperature zone growth, and its specific chemical formula is: Bi₂Te (3-x) Se x +y%wtAgI, by adjusting the Se ratio by x, the band gap is widened, and by adjusting the AgI doping amount by y, the carrier concentration is controlled, thereby further improving the overall performance of the material.

[0016] To optimize the above technical solution, the specific measures also include:

[0017] For x = 0.3 or 0.5, the corresponding y = 0.11 or 0.10.

[0018] A method for mass production of N-type bismuth telluride single-crystal thermoelectric materials includes the following steps:

[0019] Step 1: Using Bi powder, Te powder, Se powder and AgI powder as initial raw materials, weigh and mix them according to the chemical formula stoichiometric ratio;

[0020] Step 2: Pour the mixed powder obtained in Step 1 into a quartz ampoule and seal it under vacuum.

[0021] Step 3: After melting the quartz ampoule in a high-temperature swing furnace, remove it, break the sintered compound, and then reseal it into the quartz ampoule.

[0022] Step four: Using the dual-temperature zone growth method, the quartz ampoule is placed in a single crystal growth furnace and heated to cause a reaction. After the reaction is completed, the grown single crystal is obtained, namely the N-type bismuth telluride single crystal thermoelectric material.

[0023] In step one above, the purities of Bi powder, Te powder, Se powder, and AgI powder are 99.999%, 99.999%, 99.999%, and 99.99%, respectively.

[0024] The mixing time in step one above is 5 to 10 minutes.

[0025] The vacuum sealing pressure in step two above is 3 × 10⁻⁶. -3 Pa.

[0026] In step three above, the temperature of the high-temperature oscillating furnace is 1023K, and the oscillation time is 30min.

[0027] The reaction process in step four above is as follows: first, the quartz ampoule is slowly heated to 933K and kept at this temperature for 40 hours, then the quartz ampoule is slowly cooled to 713K, and finally cooled to room temperature.

[0028] In the above reaction process, the rate of slow heating is 10 K / h, the rate of slow cooling is 1.5 K / h, and the rate of cooling to room temperature is 30 K / h.

[0029] The present invention has the following beneficial effects:

[0030] (1) In terms of formulation, this invention effectively expands the band gap of the thermoelectric material by adjusting the content of Se, thereby significantly improving the performance of the material in the high-temperature range. In addition, by adjusting the doping amount of AgI and controlling the carrier concentration, the overall performance of the material is further improved.

[0031] (2) In terms of the preparation process, the raw materials are fully mixed and homogeneous compounds are formed by melting in a high-temperature swing furnace. After the sintered compound is broken up, it is repackaged into ampoules to ensure vacuum and further mix the raw materials to avoid uneven doping at the beginning and end during the cooling process. Through this series of processes, the uniformity of the material is effectively improved.

[0032] (3) This invention uses a unique dual-temperature zone growth technology to accurately establish a temperature gradient effect, resulting in materials with excellent orientation, thereby forming high-quality single crystals and improving the product quality in the field of crystal growth.

[0033] (4) The preparation process adopted in this invention is simple and easy to implement, with low production cost, large single-tube output, no need for complex equipment, no need for manual intervention in the single crystal growth process, and the preparation process has good repeatability, making it suitable for mass production of large single crystals.

[0034] (5) The single-crystal thermoelectric material Bi2Te prepared in this invention 2.7 Se 0.3 With +0.11%wtAgI, its ZT value reaches a peak of 1.4 at 335K, which is significantly superior to the ZT value of ordinary materials. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the thermoelectric material of the present invention;

[0036] Figure 2 This is a flowchart of the thermoelectric material preparation process of the present invention;

[0037] Figure 3 The ZT-T curves are for Embodiments 1 and 2 of the present invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Although the steps in this invention are arranged by reference numerals, this is not intended to limit the order of the steps. Unless the order of the steps is explicitly stated or the execution of a step requires other steps as a basis, the relative order of the steps can be adjusted. It is understood that the term "and / or" as used herein refers to and covers any and all possible combinations of one or more of the associated listed items.

[0040] This invention discloses an N-type bismuth telluride single-crystal thermoelectric material, which is prepared by dual-temperature zone growth and has the specific chemical formula Bi₂Te. (3-x) Se x +y%wtAgI, the band gap is widened by adjusting the proportion of Se by x, and the doping amount of AgI is adjusted by y to control the carrier concentration, thereby further improving the overall performance of the material. In the example, x=0.3, 0.5; y=0.11, 0.10. Example 1

[0041] To prepare N-type bismuth telluride single-crystal thermoelectric material Bi2Te 2.7 Se 0.3 Taking +0.11%wtAgI as an example, combined with Figure 2 The preparation method is described in detail:

[0042] Step 1: Using commercially available Bi, Te, Se, and AgI powders as initial raw materials, weigh and mix them according to the stoichiometric ratio of their chemical formulas. Specifically:

[0043] Using commercially available powders of high purity Bi (99.999%), Te (99.999%), Se (99.999%), and AgI (99.99%) as initial raw materials, according to Bi2Te... 2.7 Se 0.3 Weigh the sample at a stoichiometric ratio of +0.11%wtAgI;

[0044] Step two, pour the powder obtained in step one into a quartz ampoule, and heat it at 3×10⁻⁶ mm. -3 Vacuum sealing under pressure of Pa;

[0045] Step 3: Place the quartz ampoule in a 1023K swing furnace to melt and shake for 30 minutes, remove and break the sintered compound, and then reseal it into the quartz ampoule.

[0046] Step four involves placing the quartz ampoule in a single crystal growth furnace and heating it to induce a reaction. After the reaction, a single crystal, namely N-type bismuth telluride single crystal thermoelectric material, is obtained. The reaction process is as follows: the quartz ampoule is first slowly heated to 933K at a rate of 10K / h and held at this temperature for 40 hours. Then, the quartz ampoule is slowly cooled to 713K at a rate of 1.5K / h, and finally cooled to room temperature at a rate of 30K / h.

[0047] The electrical conductivity, Seebeck coefficient, and thermal conductivity of the sample in this embodiment were tested, and its ZT value was calculated. The results show that Bi₂Te 2.7 Se 0.3 The +0.11%wtAgI thermoelectric material exhibits a high average ZT value of 1.07 in the temperature range (300K~500K), peaking at 1.4 at 335K, and an average ZT value of 0.86 in the temperature range (300K~600K). Figure 3 As shown. Example 2

[0048] In Example 1, the decrease in ZT value with increasing temperature was mainly due to the bipolar effect. Therefore, in this example, the band gap of the bismuth telluride material was widened by adjusting the Se ratio to prepare the N-type bismuth telluride single-crystal thermoelectric material Bi₂Te. 2.5 Se 0.5 Taking +0.10%wtAgI as an example, combined with Figure 2 The preparation method is described in detail.

[0049] Step 1: Using commercially available high-purity Bi powder (99.999%), Te powder (99.999%), Se powder (99.999%), and AgI powder (99.99%) as initial raw materials, according to the Bi2Te... 2.5 Se 0.5 Weigh the sample at a stoichiometric ratio of +0.10%wtAgI;

[0050] Step two, pour the powder obtained in step one into a quartz ampoule, and heat it at 3×10⁻⁶ mm. -3 Vacuum sealing under pressure of Pa;

[0051] Step 3: Place the quartz ampoule in a 1023K shaking furnace for melting and shaking for 30 minutes. Remove and break the sintered compound, then reseal it into the quartz ampoule.

[0052] Step four: Place the quartz ampoule in a single crystal growth furnace and slowly heat it (10K / h) to 933K, and hold it at this temperature for 40 hours. Then, slowly cool the quartz ampoule (1.5K / h) to 713K, and finally cool it (30K / h) to room temperature to obtain the grown single crystal.

[0053] The electrical conductivity, Seebeck coefficient, and thermal conductivity of the sample in this embodiment were tested, and its ZT value was calculated. The results show that Bi₂Te 2.5 Se 0.5 The +0.10%wtAgI thermoelectric material also exhibits a high average ZT value in the temperature range (300K~500K), reaching 1.07, and peaking at 1.2 at 360K. Although the peak value decreases, the average ZT value in the temperature range (300K~600K) can still reach 0.9. Figure 3 As shown.

[0054] In summary, the single-crystal thermoelectric materials of Examples 1 to 2 have the chemical formulas Bi2Te, respectively. 2.7 Se 0.3 +0.11%wtAgI and Bi2Te 2.5 Se 0.5 +0.1%wtAgI, prepared using a dual-temperature zone growth method, from Figure 1 As can be seen, the material exhibits excellent orientation and a significantly improved carrier mobility. After AgI doping, silver ions balance the conductivity and Seebeck coefficient by adjusting the number of carriers. When the AgI doping coefficient is 0.11%wt, doping generates dislocations in the single-crystal structure, resulting in ultra-low lattice thermal conductivity, thus giving Example 1 the highest ZT peak value. Experimental measurements and calculations revealed that within the temperature range of 300K–500K, the material in Example 1 exhibits a larger average ZT value (1.07) and better temperature stability. In contrast, the matrix formulation changed from Bi2Te... 2.7 Se 0.3 Adjust to Bi2Te 2.5 Se 0.5 It can effectively widen the band gap. When the doping ratio of AgI is 0.1%wt, Example 2 has a larger average ZT value (0.9) in the temperature range of 300K to 600K, which is 4.6% higher than that of Example 1. This result shows that increasing the proportion of Se can significantly reduce the adverse effects caused by the bipolar effect, and enable the material to have better temperature stability over a wider temperature range.

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0056] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An N-type bismuth telluride single-crystal thermoelectric material, characterized in that, The N-type bismuth telluride single-crystal thermoelectric material is prepared by dual-temperature zone growth, and its specific chemical formula is: Bi₂Te (3-x) Se x +y%wtAgI, x=0.3, y=0.

11.

2. The method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 1, characterized in that, The method includes the following steps: Step 1: Using Bi powder, Te powder, Se powder and AgI powder as initial raw materials, weigh and mix them according to the chemical formula stoichiometric ratio; Step 2: Pour the mixed powder obtained in Step 1 into a quartz ampoule and seal it under vacuum. Step 3: After melting the quartz ampoule in a high-temperature swing furnace, remove it, break the sintered compound, and then reseal it into the quartz ampoule. Step four: Using the dual-temperature zone growth method, the quartz ampoule is placed in a single crystal growth furnace and heated to cause a reaction. After the reaction is completed, the grown single crystal is obtained, namely the N-type bismuth telluride single crystal thermoelectric material.

3. A method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 2, characterized in that, In step one, the purities of Bi powder, Te powder, Se powder, and AgI powder are 99.999%, 99.999%, 99.999%, and 99.99%, respectively.

4. The method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 2, characterized in that, The mixing time in step one is 5 to 10 minutes.

5. A method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 2, characterized in that, The vacuum sealing pressure in step two is 3 × 10⁻⁶. -3 Pa.

6. The method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 2, characterized in that, In step three, the temperature of the high-temperature oscillating furnace is 1023K, and the oscillation time is 30 minutes.

7. The method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 2, characterized in that, The reaction process in step four is as follows: first, the quartz ampoule is slowly heated to 933K and kept at this temperature for 40 hours, then the quartz ampoule is slowly cooled to 713K, and finally cooled to room temperature.

8. The method for mass production of N-type bismuth telluride single-crystal thermoelectric material according to claim 7, characterized in that, During the reaction, the rate of slow heating is 10 K / h, the rate of slow cooling is 1.5 K / h, and the rate of cooling to room temperature is 30 K / h.

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