A CuAgSe-based thermoelectric semiconductor crystal and its preparation method

Abstract

The invention relates to the technical field of thermoelectric semiconductor materials and discloses a CuAgSe-based thermoelectric semiconductor crystal and a preparation method thereof. The material is prepared from elemental Cu, elemental Ag and elemental Se as raw materials through a melting process and a Bridgman growth method. Compared with a CuAgSe-based thermoelectric semiconductor crystal prepared by a pressure sintering method, the material has high electrical conductivity, a slightly lower Seebeck coefficient, comparable thermal conductivity, a high thermoelectric figure of merit and high thermoelectric performance. The method controls a cooling gradient and a moving rate of a polycrystalline material in the cooling gradient to grow a CuAgSe crystal with a single high orientation. The method can significantly reduce the content of a second phase in the crystal by controlling the cooling gradient, and can directly obtain a CuAgSe crystal with a single high orientation without the need for removing the second phase, thereby significantly improving the utilization rate of the CuAgSe polycrystalline raw material.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoelectric semiconductor materials, and in particular to a CuAgSe-based thermoelectric semiconductor crystal and a preparation method thereof. Background Art

[0002] Thermoelectric materials are functional materials that convert heat energy into electrical energy. Among them, CuAgSe is a highly promising thermoelectric material. However, CuAgSe is difficult to synthesize, resulting in limited research and application. Currently, the synthesis of CuAgSe materials mainly involves melting and chemical methods. Chemical methods include electrochemical synthesis and template synthesis. However, chemical methods are complex and produce impure products, making it difficult to effectively apply CuAgSe materials prepared by chemical methods in the field of thermoelectric semiconductors. The melting method, on the other hand, is simple and can be mass-produced. For example, the literature "Journal of Materials Chemistry A 2015, 3, 13662-13670.》 discloses a method for preparing CuAgSe-based thermoelectric semiconductor crystals, and another example is a method for preparing a homogeneous bulk thermoelectric material by a one-step in-situ reaction disclosed in publication number CN105990511B; the above method uses Cu powder, Ag powder and Se powder to first press into blocks, and then pressurizes and sinters the blocks to form CuAgSe semiconductor crystal materials. This method has high density, uniform composition and can be mass-produced, but the CuAgSe crystal materials produced by the hot pressing and sintering method are small in size.

[0003] Therefore, in order to obtain larger CuAgSe crystal materials, the existing technology adopts the floating zone method to prepare CuAgSe crystal materials, such as the highly preferentially oriented CuAgSe material and its preparation method and application disclosed in publication number CN118317678A. This method can obtain large-sized and more single-oriented CuAgSe polycrystalline materials. In addition, the method also points out that the crystal planes of the crystal material obtained by conventional melt annealing treatment are chaotic, and it cannot be guaranteed that the grown crystals can grow in layers, and it is impossible to obtain larger-sized crystal materials; while in the optical floating zone method, the second phase inside the crystal tends to melt in the liquid phase during the optical melting process, so that the second phase will be concentrated on the top of the finally formed polycrystalline material. By removing the second phase, a crystal material with highly preferential phase properties can be obtained, which also shows that the optical floating zone method has the problem of low raw material utilization. Summary of the Invention

[0004] In order to overcome the problem in the prior art of low raw material utilization caused by the generation of a second phase during the melt growth of polycrystalline materials, the present invention provides a CuAgSe-based thermoelectric semiconductor crystal and a preparation method thereof. The material is produced by a Bridgman growth method. Compared with a CuAgSe-based thermoelectric semiconductor crystal produced by a pressure sintering method, the material has high electrical conductivity, a slightly lower Seebeck coefficient, comparable thermal conductivity, a high thermoelectric figure of merit, and high thermoelectric performance. The method can obtain CuAgSe crystals with high single orientation by controlling the cooling gradient and the movement rate of the polycrystalline material in the cooling gradient. The method can significantly reduce the content of the second phase in the crystal by controlling the cooling gradient, and can directly obtain CuAgSe crystals with high single orientation without the need for removing the second phase, thereby significantly improving the utilization rate of the CuAgSe polycrystalline raw material.

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

[0006] A CuAgSe-based thermoelectric semiconductor crystal has a molecular formula of CuAgSe. The CuAgSe-based thermoelectric semiconductor crystal is produced from elemental Cu, elemental Ag, and elemental Se as raw materials through a melt treatment and a Bridgman growth method. The Bridgman growth method comprises high-temperature melting, gradient cooling growth, and low-temperature insulation. The gradient cooling growth conditions are: a cooling gradient of 15-25°C / cm, and a migration rate of the polycrystalline material in the cooling gradient of 0.01-3 mm / h.

[0007] Preferably, the moving rate is 1.3-1.5 mm / h.

[0008] Preferably, the thermoelectric figure of merit of the CuAgSe-based thermoelectric semiconductor crystal is 0.5-0.7, and within the range of 300 K to 450 K, the average thermoelectric figure of merit is 0.4-0.6.

[0009] Preferably, the CuAgSe-based thermoelectric semiconductor crystal has a diameter of 10-80 mm and a length of 10-100 cm.

[0010] The present invention provides a CuAgSe-based thermoelectric semiconductor crystal. The material is produced by melt quenching and Bridgman growth method using elemental Cu, elemental Ag and elemental Se as raw materials. The metal element can be directly processed without pre-processing the raw materials, which simplifies the process. The material is produced by the Bridgman growth method. The CuAgSe-based thermoelectric semiconductor crystal obtained by the production has high single orientation, large grains and large size. Compared with the CuAgSe-based thermoelectric semiconductor crystal produced by the pressure sintering method, the material has high electrical conductivity, a slightly lower Seebeck coefficient, comparable thermal conductivity, high thermoelectric figure of merit and high thermoelectric performance.

[0011] When the present invention adopts the method disclosed in the prior art CN118317678A to grow CuAgSe crystals, it is found that when using the optical floating zone method for crystal growth, more second phases will be produced. These second phases will tend to dissolve in the melt. As the melt moves, the second phases will be continuously concentrated at the top of the crystal. Subsequently, only the top needs to be removed to obtain a CuAgSe crystal with a single high orientation. However, when using the Bridgman growth method, it is found that by controlling the descent rate, the appearance of the second phase can be suppressed, and the content of the second phase in the crystal can be significantly reduced. It can ensure that the CuAgSe-based thermoelectric semiconductor crystal can be used without removing the second phase, and can significantly improve the utilization rate of the CuAgSe polycrystalline raw materials.

[0012] A method for preparing the above-mentioned CuAgSe-based thermoelectric semiconductor crystal comprises the following steps:

[0013] Step 1: Place elemental Cu, elemental Ag, and elemental Se into a crucible and seal it in a vacuum, then melt the sealed crucible to produce a CuAgSe polycrystalline raw material;

[0014] Step 2: Place the CuAgSe polycrystalline raw material in a crucible and vacuum seal it, place the sealed crucible in a Bridgman growth device and perform high-temperature melting, gradient cooling growth and low-temperature insulation in sequence to produce a CuAgSe-based thermoelectric semiconductor crystal.

[0015] Preferably, the conditions for the melt treatment in step 1 include: a melt temperature of 950-1100°C and a heating rate of 2-10°C / min.

[0016] Preferably, the conditions for the melt treatment in step 1 further include: a swing time of 0.5 to 3 h, and a swing rate of 10 to 30 r / min.

[0017] Preferably, the heating rate of the high-temperature melting in step 2 is 1-2.5°C / min.

[0018] Preferably, in step 2, the bottom of the crucible is conical with a taper of 17-54°, ​​a crucible diameter of 10-80 mm, and a crucible length of 200-400 mm.

[0019] Preferably, the crucible is a double-layer crucible.

[0020] Preferably, the temperature of the low-temperature insulation in step 2 is 550-500°C.

[0021] Compared with the existing technology, this application has the following technical effects:

[0022] (1) Compared with CuAgSe-based thermoelectric semiconductor crystals made by pressure sintering, this material has high electrical conductivity, slightly lower Seebeck coefficient, comparable thermal conductivity, high thermoelectric figure of merit, and high thermoelectric performance;

[0023] (2) This method can obtain CuAgSe crystals with high single orientation by controlling the cooling gradient and the movement rate of the polycrystalline material in the cooling gradient;

[0024] (3) This method can significantly reduce the content of the second phase in the crystal by controlling the cooling gradient, and can directly obtain CuAgSe crystals with high single orientation without removing the second phase, which significantly improves the utilization rate of CuAgSe polycrystalline raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the X-ray diffraction pattern of the CuAgSe-based thermoelectric semiconductor crystal of Example 1.

[0026] Figure 2 Surface morphology and mapping of the CuAgSe-based thermoelectric semiconductor crystal of Example 1.

[0027] Figure 3 The conductivity line graph of the CuAgSe-based thermoelectric semiconductor crystals of Example 1 and Comparative Example 1 in the range of 300K-450K is perpendicular to the axis and parallel to the axis. Example 1 is parallel to the axis and perpendicular to the axis, and Comparative Example 1 is Document 1.

[0028] Figure 4 The Seebeck coefficient line graph of the CuAgSe-based thermoelectric semiconductor crystals of Example 1 and Comparative Example 1 in the range of 300K-450K is perpendicular to the axis and parallel to the axis. Example 1 is parallel to the axis and perpendicular to the axis, and Comparative Example 1 is Reference 1.

[0029] Figure 5 The thermal conductivity line graph of the CuAgSe-based thermoelectric semiconductor crystal in the range of 300K-450K is perpendicular to the axis and parallel to the axis for Example 1 and Comparative Example 1. Example 1 is parallel to the axis and perpendicular to the axis, and Comparative Example 1 is Reference 1.

[0030] Figure 6 Dimensionless figure of merit broken line graph of CuAgSe-based thermoelectric semiconductor crystal in the range of 300K-450K of Example 1 and Comparative Example 1, Example 1 is parallel to the axis direction and perpendicular to the axis direction, and Comparative Example 1 is Reference 1. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the embodiments.

[0032] Example 1:

[0033] A method for preparing a CuAgSe-based thermoelectric semiconductor crystal comprises the following steps:

[0034] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0035] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 15 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 1.4 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to produce a CuAgSe-based thermoelectric semiconductor crystal with a length of 30 mm and a diameter of 50 mm. The low-temperature insulation time was 12 hours.

[0036] Example 2:

[0037] A method for preparing a CuAgSe-based thermoelectric semiconductor crystal comprises the following steps:

[0038] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0039] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 15 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 1.3 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to produce a CuAgSe-based thermoelectric semiconductor crystal with a length of 30 mm and a diameter of 50 mm. The low-temperature insulation time was 12 hours.

[0040] Example 3:

[0041] A method for preparing a CuAgSe-based thermoelectric semiconductor crystal comprises the following steps:

[0042] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0043] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 15 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 1.5 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to produce a CuAgSe-based thermoelectric semiconductor crystal with a length of 30 mm and a diameter of 50 mm. The low-temperature insulation time was 12 hours.

[0044] Example 4:

[0045] A method for preparing a CuAgSe-based thermoelectric semiconductor crystal comprises the following steps:

[0046] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 950°C, and keep it warm for 0.5 h to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 10 r / min for 0.5 h to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0047] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 10 mm, a length of 200 mm, a conical bottom, and a taper of 17°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 950 ℃ (heating rate was 2 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 15 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 0.01 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to produce a CuAgSe-based thermoelectric semiconductor crystal with a length of 10 mm and a diameter of 10 mm. The low-temperature insulation time was 12 hours.

[0048] Example 5:

[0049] A method for preparing a CuAgSe-based thermoelectric semiconductor crystal comprises the following steps:

[0050] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1100°C, and keep it warm for 3 hours to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 30 r / min for 3 hours to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0051] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 80 mm, a length of 400 mm, a conical bottom and a taper of 54°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1100 ℃ (heating rate was 10 ℃ / min), the quartz crucible was kept in the melting zone for 12 h, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 25 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 3 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 550 ℃) for low-temperature insulation to produce a CuAgSe-based thermoelectric semiconductor crystal with a length of 80 mm and a diameter of 100 mm. The low-temperature insulation time was 24 h.

[0052] Comparative Example 1:

[0053] Compared with Example 1, in Comparative Example 1, the pressure sintering method disclosed in Reference 1: Journal of Materials Chemistry A2015, 3, 13662-13670 was used to prepare a CuAgSe-based thermoelectric semiconductor crystal. The prepared CuAgSe-based thermoelectric semiconductor crystal had a diameter of 5 mm and a length of 5 mm.

[0054] Comparative Example 2:

[0055] Compared with Example 1, in step 2 of Comparative Example 2, the quartz crucible is slowly moved in the gradient cooling zone at a rate that is too low, namely, 0.2 mm / h, and comprises the following steps:

[0056] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0057] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 15 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 0.2 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to form a CuAgSe-based thermoelectric semiconductor crystal, and the low-temperature insulation time was 12 hours.

[0058] Comparative Example 3:

[0059] Compared with Example 1, in step 2 of Comparative Example 3, the quartz crucible is slowly moved in the gradient cooling zone at a rate that is too high, and the rate is 3 mm / h, comprising the following steps:

[0060] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0061] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10-3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 15 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 3 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to form a CuAgSe-based thermoelectric semiconductor crystal, and the low-temperature insulation time was 12 hours.

[0062] Comparative Example 4:

[0063] Compared with Example 1, the crucible in step 2 of Comparative Example 4 is a single-layer crucible, and the other conditions are the same as those in Example 1.

[0064] Comparative Example 5:

[0065] Compared with Example 1, the quartz crucible in step 2 of Comparative Example 5 is a flat-bottomed dry pot, and the other conditions are the same as those in Example 1.

[0066] Comparative Example 6:

[0067] Compared with Example 1, the temperature of the melting zone in step 2 of Comparative Example 6 is too low. The temperature of the melting zone is 700° C., and the other conditions are the same as those in Example 1.

[0068] Comparative Example 7:

[0069] Compared with Example 1, the temperature reduction gradient in the gradient cooling zone of step 2 in Comparative Example 7 is too small, and the temperature reduction gradient is 5°C / cm, which includes the following steps:

[0070] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0071] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10 -3Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 5 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 1.4 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to form a CuAgSe-based thermoelectric semiconductor crystal, and the low-temperature insulation time was 12 hours.

[0072] Comparative Example 8:

[0073] Compared with Example 1, the temperature reduction gradient in the gradient cooling zone of step 2 in Comparative Example 8 is too large, and the temperature reduction gradient is 40°C / cm, which includes the following steps:

[0074] Step 1: Weigh elemental Cu, elemental Ag, and elemental Se in a molar ratio of 1:1:1. The purity of elemental Cu, elemental Ag, and elemental Se is greater than 99.9%. Place elemental Cu, elemental Ag, and elemental Se in a quartz crucible and vacuum seal it. Place the sealed crucible in a rocking furnace, raise the temperature of the rocking furnace to 1000°C, and keep it warm for 1 hour to completely melt the metal elements in the crucible. Then rock it at a rocking speed of 20 r / min for 1 hour to fully mix the raw materials. Cool it to produce CuAgSe polycrystalline raw materials.

[0075] Step 2: Take 80 g of the above CuAgSe polycrystalline raw material and place it in a quartz crucible (a double-layer quartz crucible with a diameter of 50 mm, a length of 200 mm, a conical bottom and a taper of 30°), and evacuate to 10 -3 Pa, filled with argon, and then evacuated to 10 -3 Pa, after three cycles, the quartz crucible was sealed with a hydrogen-oxygen flame; the quartz crucible was placed vertically in the melting zone of the vertical growth furnace, the temperature of the melting zone was set to 1000 ℃ (heating rate was 3 ℃ / min), the quartz crucible was kept in the melting zone for 12 hours, and then the quartz crucible was moved to the gradient cooling zone below the melting zone (the temperature of the gradient cooling zone was 900 ℃, and the cooling gradient was 40 ℃ / cm). The quartz crucible was slowly moved in the gradient cooling zone at a moving rate of 1.4 mm / h until all the melt was crystallized. The quartz crucible was then moved to the low-temperature zone (the temperature of the low-temperature zone was 500 ℃) for low-temperature insulation to form a CuAgSe-based thermoelectric semiconductor crystal, and the low-temperature insulation time was 12 hours.

[0076] Figure 1is the X-ray diffraction pattern of the CuAgSe-based thermoelectric semiconductor crystal of Example 1, from Figure 1 It can be seen that the grown CuAgSe-based thermoelectric semiconductor crystal is a single phase.

[0077] Figure 2 The surface morphology and mapping of the CuAgSe-based thermoelectric semiconductor crystal of Example 1 are shown in FIG. Figure 2 It can be seen that the distribution of various elements in the CuAgSe-based thermoelectric semiconductor crystal is very uniform.

[0078] Figure 3 The conductivity line graph of the CuAgSe-based thermoelectric semiconductor crystals in the range of 300K-450K perpendicular to the axis and parallel to the axis of Example 1 and Comparative Example 1 is shown in FIG. Figure 3 It can be seen that in the range of 300-450K, the conductivity of the crystal in the directions perpendicular to the axis and parallel to the axis is higher than that of comparative example 1.

[0079] Figure 4 The Seebeck coefficients of the CuAgSe-based thermoelectric semiconductor crystals in the range of 300K-450K are shown in FIG1 , which are perpendicular to the axis and parallel to the axis. Figure 4 It can be seen that in the range of 300-450K, the Seebeck coefficients of the crystal perpendicular to the axis and parallel to the axis are lower than those of comparative example 1.

[0080] Figure 5 The thermal conductivity of the CuAgSe-based thermoelectric semiconductor crystal in the range of 300K-450K perpendicular to the axis and parallel to the axis is shown in FIG. Figure 5 It can be seen that in the range of 300-450K, the thermal conductivity of the crystal perpendicular to the axis and parallel to the axis is comparable to that of Comparative Example 1.

[0081] Figure 6 The dimensionless figure of merit zT value broken line graph of CuAgSe based thermoelectric semiconductor crystal in the range of 300K-450K of Example 1 and Comparative Example 1 is shown in FIG. Figure 6 It can be seen that in the range of 300-450K, the dimensionless merit zT values ​​of the crystal perpendicular to the axis and parallel to the axis are both higher than those of comparative example 1.

[0082] Test example:

[0083] The raw material utilization rates of the CuAgSe-based thermoelectric semiconductor crystals prepared in Examples 1 to 3, Comparative Examples 2 and 3 were calculated, and the second phase content in the prepared CuAgSe-based thermoelectric semiconductor crystals was tested and the raw material utilization rates were calculated.

[0084] The second phase content is tested using X-ray diffraction patterns to calculate the raw material utilization rate.

[0085] Raw material utilization rate = [(CuAgSe-based thermoelectric semiconductor crystal mass - second phase mass) / CuAgSe-based thermoelectric semiconductor crystal mass] × 100%. The test results are shown in Table 1.

[0086] Table 1 Test results

[0087]

[0088] As shown in Table 1, the raw material utilization rates of Examples 1 to 3 are all above 99.95%, while the raw material utilization rates of Comparative Examples 2 and 3 are all less than 99%. The above results show that the movement rate has a significant effect on the content of the second phase in the grown CuAgSe-based thermoelectric semiconductor crystals. When the movement rate is between 1.2 and 1.5 mm / h, the content of the second phase can be ensured to be as low as 0.0005%, ensuring that the CuAgSe-based thermoelectric semiconductor crystals can be used without the need for second phase removal processing. The results of Comparative Examples 2 and 3 show that both too high and too low movement rates will result in the content of the second phase in the obtained CuAgSe-based thermoelectric semiconductor crystals being higher than 0.01%. CuAgSe-based thermoelectric semiconductor crystals with a second phase content higher than 0.01% require further removal of the second phase before they can be used. In addition, suppressing the generation of the second phase can also improve the raw material utilization rate of the CuAgSe polycrystalline raw material, and can obtain a larger-sized CuAgSe-based thermoelectric semiconductor at one time.

[0089] By analyzing the results of Example 1, Comparative Example 4 and Comparative Example 5, it was found that the crucible has a significant effect on the growth of CuAgSe-based thermoelectric semiconductor crystals. A single-layer crucible was used in Comparative Example 4. As a result, the crucible in Comparative Example 4 broke during the melting stage and subsequent solution growth was impossible. A flat-bottomed crucible was used in Comparative Example 5. It was found that the flat-bottomed crucible was prone to multiple crystal nuclei. During the subsequent crystal growth, too many crystal nuclei were oriented along multiple crystal nuclei at the same time, resulting in a reduction in the single orientation of the crystal.

[0090] By analyzing the results of Example 1 and Comparative Example 6, it was found that when the melting temperature of Comparative Example 6 was too low, the polycrystalline raw material could not be melted and subsequent crystal growth could not be performed.

[0091] By analyzing the results of Example 1, Comparative Example 7 and Comparative Example 8, it was found that the cooling gradient also has a significant effect on the growth of CuAgSe-based thermoelectric semiconductor crystals. If the cooling gradient is too small, the grains will be too small, and if the temperature gradient is too large, it will affect the orientation of the crystal.

[0092] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent transformation made to the above embodiment based on the technical essence of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a CuAgSe-based thermoelectric semiconductor crystal, characterized in that: The following steps are involved: Step 1: Place elemental Cu, elemental Ag, and elemental Se into a crucible and seal it in a vacuum, then melt the sealed crucible to produce a CuAgSe polycrystalline raw material. The melting temperature of the melting process is 950-1100°C, and the heating rate of the melting process is 2-10°C / min. Step 2: placing a CuAgSe polycrystalline raw material in a crucible and vacuum-sealing it, placing the sealed crucible in a Bridgman growth device and sequentially performing high-temperature melting, gradient cooling growth, and low-temperature insulation to form a CuAgSe-based thermoelectric semiconductor crystal; the conditions for the gradient cooling growth are: a cooling gradient of 15-25°C / cm, and a movement rate of the polycrystalline material in the cooling gradient of 1.3-1.5 mm / h; the diameter of the CuAgSe-based thermoelectric semiconductor crystal is 10-80 mm and the length is 10-100 mm; the crucible is a double-layer crucible, the bottom of the crucible is conical, the taper of the cone is 17-54°, ​​the diameter of the crucible is 10-80 mm, the length of the crucible is 20-40 cm, and the high-temperature melting temperature is 950-1100°C.

2. The preparation method according to claim 1, wherein The thermoelectric figure of merit of the CuAgSe-based thermoelectric semiconductor crystal is 0.5-0.

7.

3. The preparation method according to claim 1, wherein The CuAgSe-based thermoelectric semiconductor crystal has an average thermoelectric figure of merit of 0.4-0.6 in the range of 300 K to 450 K.

4. The preparation method according to claim 1, wherein The melting conditions in step 1 also include: a swing time of 0.5 to 3 h and a swing rate of 10 to 30 r / min.

5. The preparation method according to claim 1, wherein The heating rate of the high-temperature melting in step 2 is 1-2.5°C / min.

6. The preparation method according to claim 1, wherein The temperature of the low temperature insulation in step 2 is 550~500℃.

7. The preparation method according to claim 1, wherein The raw material utilization rate is above 99.95%, and the raw material utilization rate = [(CuAgSe-based thermoelectric semiconductor crystal mass - second phase mass) / CuAgSe-based thermoelectric semiconductor crystal mass] ╳ 100%.

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