A homogeneous Mg3(Sb,Bi)2 alloy prepared by a formation energy-controlled melting method and its preparation method
By doping Zn and Nd into Mg3(Sb,Bi)2 alloy and controlling the melting preparation process, the phase separation and compositional segregation problems caused by the atomic stress imbalance of Sb and Bi were solved, the thermoelectric properties and structural stability of the alloy were improved, and it is suitable for mass production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-04-02
- Publication Date
- 2026-06-23
AI Technical Summary
The existing melting method for preparing Mg3(Sb,Bi)2 alloy suffers from phase separation and compositional segregation caused by stress imbalance between Sb and Bi atoms. This results in the precipitation of elemental Bi, low carrier concentration, limited improvement of thermoelectric figure of merit, and reduced alloy structural stability, making it unable to meet the long-term service requirements of extreme environments such as deep space exploration.
An alloy with the chemical formula Mg3.38-xZnx(Sb,Bi)2Nd0.02 was prepared by using a melting method based on formation energy control, through the design of appropriate excess of Zn doping and Mg, combined with Nd doping. The reaction temperature and pressure during the melting process were controlled by using a graphite crucible and a pointed bottom quartz tube under vacuum sealing. Subsequently, spark plasma sintering was performed to achieve homogenization of the alloy.
It effectively compensates for the volatilization loss of Mg, avoids phase separation and component segregation, increases carrier concentration, improves thermoelectric performance and alloy structure stability, and achieves a thermoelectric figure of merit of 1.36, making it suitable for mass production.
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Figure CN122256752A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of thermoelectric materials technology. Background Technology
[0002] Thermoelectric materials are functional materials that utilize the Seebeck and Peltier effects to convert heat energy into electrical energy. They have gained widespread attention due to their advantages such as small size, no noise, no greenhouse gas emissions, and wide range of applications. Among numerous thermoelectric material systems, Mg3(Sb,Bi)2 alloy, as a novel mid-temperature thermoelectric material, possesses abundant raw material reserves, environmental friendliness, and excellent thermoelectric performance. It shows broad application prospects in deep space exploration, waste heat recovery, and clean energy power generation, becoming one of the core research directions in near-room temperature to mid-temperature thermoelectric materials.
[0003] However, existing technologies face key bottlenecks: while the mainstream ball milling process for preparing Mg3(Sb,Bi)2 alloys achieves excellent thermoelectric properties, it is complex, inefficient, and unsuitable for mass production. Conversely, in the melt-processing method, the stress imbalance between Sb and Bi atoms leads to phase separation and compositional segregation, resulting in the precipitation of elemental Bi and a low carrier concentration, limiting the improvement of thermoelectric figure of merit. Furthermore, the microstructural inhomogeneity caused by phase separation significantly reduces the alloy's structural stability and service reliability, failing to meet the long-term service requirements of extreme environments such as deep space exploration. Therefore, developing a simple, low-cost melt-processing method that can effectively improve the phase purity of Mg3(Sb,Bi)2 alloys has significant engineering application value. Summary of the Invention
[0004] This invention aims to address the problems of phase separation and compositional segregation caused by the stress imbalance of Sb and Bi atoms in the existing molten preparation of Mg3(Sb,Bi)2 alloys, which leads to the precipitation of elemental Bi, low carrier concentration, limited improvement of thermoelectric figure of merit, and reduced alloy structural stability. Therefore, this invention provides a homogeneous Mg3(Sb,Bi)2 alloy prepared by a formation energy-controlled melting method and its preparation method.
[0005] A homogeneous Mg3(Sb,Bi)2 alloy prepared by a formation energy-controlled melting method, wherein the general chemical formula of the homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy-controlled melting method is Mg 3.38-x Zn x (Sb,Bi)2Nd 0.02 Where x = 0.1~0.3.
[0006] A method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on formation energy-controlled melting, comprising the following steps:
[0007] I. According to the general chemical formula Mg 3.38-x Znx (Sb,Bi)2Nd 0.02 The raw materials are weighed according to the stoichiometric ratio, where x = 0~0.3;
[0008] 2. Place the raw material in a threaded graphite crucible and wrap it with iron foil, then place it in a pointed-bottom quartz tube and vacuum seal it to obtain a sealed pointed-bottom quartz tube.
[0009] 3. Place the sealed pointed-bottom quartz tube in a muffle furnace, first heat it to 550℃~590℃, then heat it to 700℃~750℃, then heat it to 1100℃~1200℃, and finally cool it to room temperature with the furnace to obtain the smelted alloy.
[0010] IV. The smelted alloy is subjected to spark plasma sintering to obtain a homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy controlled melting method.
[0011] The beneficial effects of this invention are:
[0012] 1. In terms of formulation, this invention can effectively compensate for the volatilization loss of Mg during the smelting process by designing an appropriate excess of Zn doping and Mg. The specific amount of Zn doping can play a role in regulating phase purity without introducing new impurity phases or destroying the Mg3(Sb,Bi)2 crystal structure, thus avoiding phase separation and compositional segregation, achieving a dual guarantee of improved phase purity and alloy structure stability. Nd doping effectively regulates the carrier concentration and effectively improves thermoelectric performance.
[0013] 2. In terms of preparation process, the present invention adopts Zn doping to smooth the total energy fluctuation of the system and rapidly heats up to cross the violent reaction temperature between Mg and graphite crucible, which can effectively improve homogenization.
[0014] 3. The preparation process adopted in this invention is simple and easy to implement, with low production cost and large single-tube output. It does not require complex and expensive equipment. The preparation process of Zn-doped homogeneous Mg3(Sb,Bi)2 alloy material has good repeatability and is suitable for mass production.
[0015] 4. The Zn and Nd co-doped homogeneous Mg3(Sb,Bi)2 alloy prepared by this invention can achieve a thermoelectric figure of merit of 1.36 at 723K through regulation, providing core technical support for industrial applications. Attached Figure Description
[0016] Figure 1 This is a diagram showing the heating-cooling process of the muffle furnace in step three of Example 1;
[0017] Figure 2 The image shows the macroscopic morphology of the homogeneous Mg3(Sb,Bi)2 alloy prepared in Example 1.
[0018] Figure 3 The images show the XRD patterns of the homogeneous Mg3(Sb,Bi)2 alloys prepared in Example 1, Comparative Experiment 1, and Experiment 2.
[0019] Figure 4 The images show SEM (left) and EDS (right) images of the homogeneous Mg3(Sb,Bi)2 alloys prepared in Example 1, Comparative Experiment 1, and Comparative Experiment 2. (a) is the Mg3(Sb,Bi)2 alloy prepared in Comparative Experiment 1. 3.3 Zn 0.1 Sb 1.5 Bi 0.5 (b) Mg prepared for comparison experiment 2 3.4 Sb 1.5 Bi 0.5 (c) is the Mg prepared in Example 1. 3.28 Zn 0.1 Sb 1.5 Bi 0.5 Nd 0.02 ;
[0020] Figure 5 The graphs show the thermoelectric properties of the homogeneous Mg3(Sb,Bi)2 alloy prepared in Example 1 and Comparative Experiment 1 as a function of temperature. (a) Electrical conductivity, (b) Seebeck coefficient, (c) Power factor, (d) Thermal conductivity, and (e) Thermoelectric figure of merit. Detailed Implementation
[0021] Specific Implementation Method 1: This implementation method describes a homogeneous Mg3(Sb,Bi)2 alloy prepared using a formation energy-controlled melting method. The general chemical formula of the homogeneous Mg3(Sb,Bi)2 alloy prepared using this method is Mg. 3.38-x Zn x (Sb,Bi)2Nd 0.02 Where x = 0.1~0.3.
[0022] The beneficial effects of this specific implementation method are:
[0023] 1. In terms of formulation, this specific implementation method can effectively compensate for the volatilization loss of Mg during the smelting process by designing an appropriate excess of Zn doping and Mg. The specific amount of Zn doping can play a role in regulating phase purity without introducing new impurity phases or destroying the Mg3(Sb,Bi)2 crystal structure, avoiding phase separation and compositional segregation, and achieving a dual guarantee of phase purity improvement and alloy structure stability. Nd doping effectively regulates the carrier concentration and effectively improves thermoelectric performance.
[0024] 2. In terms of preparation process, this specific implementation method adopts Zn doping to smooth the total energy fluctuation of the system and rapidly heats up to cross the violent reaction temperature between Mg and the graphite crucible, which can effectively improve homogenization.
[0025] 3. The preparation process used in this specific embodiment is simple and easy to implement, with low production cost and large single-tube output. It does not require complex and expensive equipment. The preparation process of Zn-doped homogeneous Mg3(Sb,Bi)2 alloy material has good repeatability and is suitable for mass production.
[0026] 4. The Zn and Nd co-doped homogeneous Mg3(Sb,Bi)2 alloy prepared in this specific embodiment can achieve a thermoelectric figure of merit of 1.36 at 723K through regulation, providing core technical support for industrial applications.
[0027] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the thermoelectric figure of merit of the homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy-controlled melting method is 1.36 at 723K. Everything else is the same as in Specific Implementation Method One.
[0028] Specific Implementation Method 3: This implementation method describes a method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on a formation energy-controlled melting method, which is carried out according to the following steps:
[0029] I. According to the general chemical formula Mg 3.38-x Zn x (Sb,Bi)2Nd 0.02 The raw materials are weighed according to the stoichiometric ratio, where x = 0.1~0.3;
[0030] 2. Place the raw material in a threaded graphite crucible and wrap it with iron foil, then place it in a pointed-bottom quartz tube and vacuum seal it to obtain a sealed pointed-bottom quartz tube.
[0031] 3. Place the sealed pointed-bottom quartz tube in a muffle furnace, first heat it to 550℃~590℃, then heat it to 700℃~750℃, then heat it to 1100℃~1200℃, and finally cool it to room temperature with the furnace to obtain the smelted alloy.
[0032] IV. The smelted alloy is subjected to spark plasma sintering to obtain a homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy controlled melting method.
[0033] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method Three in that the raw materials mentioned in step one are Bi granules, Sb blocks, Mg scraps, Zn powder, and Nd blocks. Everything else is the same as in Specific Implementation Method Three.
[0034] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Three or Four in that: the average particle size of the Bi particles is 1mm~3mm; the average particle size of the Sb blocks is 3mm~5mm; the average particle size of the Mg shavings is 2mm~3mm; the average particle size of the Zn powder is 0.5mm~1mm; and the average particle size of the Nd blocks is 3mm~5mm. Everything else is the same as in Specific Implementation Method Three or Four.
[0035] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods Three to Five in that the purity of the raw materials mentioned in Step One is 99.99%. Everything else is the same as in Specific Implementation Methods Three to Five.
[0036] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods Three to Six in that the vacuum sealing pressure in the sealed pointed-bottom quartz tube described in step two is 3 × 10⁻⁶. -3 Pa~5×10 -3 Pa. The rest is the same as in any of the specific embodiments three to six.
[0037] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods Three to Seven in that: in step three, the temperature is first increased to 550℃~590℃ at a rate of 0.01℃ / min~10℃ / min, then increased to 700℃~750℃ at a rate of 8℃ / min~10℃ / min, then increased to 1100℃~1200℃ at a rate of 0.01℃ / min~10℃ / min, and finally cooled to room temperature in the furnace. Everything else is the same as in Specific Implementation Methods Three to Seven.
[0038] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods Three to Eight in that the spark plasma sintering described in step four is specifically carried out according to the following steps: holding at a pressure of 30MPa~35MPa and a temperature of 750℃~800℃ for 2min~5min. Everything else is the same as in Specific Implementation Methods Three to Eight.
[0039] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods Three to Nine in that, under a pressure of 30MPa to 35MPa, the temperature is increased to 700℃ to 750℃ over 2 to 5 minutes, and then further increased to 750℃ to 800℃ over 5 to 10 minutes. Everything else is the same as Specific Implementation Methods Three to Nine.
[0040] The beneficial effects of the present invention are verified using the following embodiments:
[0041] Example 1, combined with Figure 1 Detailed explanation:
[0042] A method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on formation energy-controlled melting, comprising the following steps:
[0043] I. According to the chemical formula Mg 3.28 Zn 0.1 Sb 1.5 Bi 0.5 Nd 0.02 Weigh the raw materials according to their stoichiometric ratio;
[0044] 2. Place the raw material in a threaded graphite crucible and wrap it with iron foil, then place it in a pointed-bottom quartz tube and vacuum seal it to obtain a sealed pointed-bottom quartz tube.
[0045] 3. Place the sealed pointed-bottom quartz tube in a muffle furnace, first raise the temperature to 580°C at 1°C / min, then raise it to 700°C at 10°C / min, then raise it to 1200°C at 5°C / min, and finally cool it to room temperature with the furnace to obtain the smelted alloy.
[0046] 4. The smelted alloy is placed in a spark plasma sintering furnace. Under a pressure of 30 MPa, the temperature is raised to 700℃ in 5 minutes, then raised to 750℃ in 2 minutes, and held at 30 MPa and 750℃ for 2 minutes to obtain a homogeneous Mg3(Sb,Bi)2 alloy.
[0047] The raw materials mentioned in step one are Bi granules, Sb blocks, Mg scraps, Zn powder, and Nd blocks.
[0048] The average particle size of the Bi particles is 2 mm; the average particle size of the Sb blocks is 3 mm; the average particle size of the Mg shavings is 3 mm; the average particle size of the Zn powder is 0.5 mm; and the average particle size of the Nd blocks is 5 mm.
[0049] The purity of the raw materials mentioned in step one is 99.99%.
[0050] The vacuum sealing pressure in the sealed pointed-bottom quartz tube described in step two is 3 × 10⁻⁶. -3 Pa.
[0051] Comparative Experiment 1: The difference between this implementation method and Specific Implementation Method 1 is that in step 1, the chemical formula is Mg 3.3 Zn 0.1 Sb 1.5 Bi 0.5 Weigh the raw materials according to the stoichiometric ratio. Everything else is the same as in Specific Implementation Method 1.
[0052] Comparative Experiment 2: This implementation method differs from Specific Implementation Method 1 in that: in step one, the chemical formula is Mg 3.4 Sb1.5 Bi 0.5 The raw materials are weighed according to the stoichiometric ratio; and since the sample itself cannot be sintered, step four is omitted. Everything else is the same as in Specific Implementation Method One.
[0053] Figure 2 The figure shows the macroscopic morphology of the homogeneous Mg3(Sb,Bi)2 alloy prepared in Example 1. As can be seen from the figure, the homogeneous Mg3(Sb,Bi)2 alloy prepared in Example 1 has uniform composition, high density, and no obvious pores or impurities, and its overall quality is excellent and stable.
[0054] Figure 3 The images show the XRD patterns of the homogeneous Mg3(Sb,Bi)2 alloys prepared in Example 1, Comparative Experiment 1, and Comparative Experiment 2. As can be seen from the images, the pure Mg3(Sb,Bi)2 sample obtained from Comparative Experiment 2 exhibits a significant Bi elemental peak, indicating low alloy phase purity. After Zn incorporation, the alloy phase purity significantly improves, showing good matching with the Mg3Sb2 standard PDF card. Furthermore, the phase purity of the corresponding sample does not change significantly with increasing Zn content. The Zn and Nd co-doped sample in Example 1 also maintains good phase purity.
[0055] Mg prepared in Comparative Experiment 1 3.3 Zn 0.1 Sb 1.5 Bi 0.5 The alloy was tested, and the actual composition, calculated using Sb1.5 normalization, was Mg. 2.83 Zn 0.02 Sb 1.5 0Bi 0.44 ;Comparative Experiment 2 prepared Mg 3.4 Sb 1.5 Bi 0.5 The alloy was tested, and the actual composition, calculated using Sb1.5 normalization, was Mg. 2.90 Sb 1.50 Bi 1.12 ; Regarding the Mg prepared in Example 1 3.28 Zn 0.1 Sb 1.5 Bi 0.5 Nd 0.02 Tests were conducted, and the actual composition was calculated to be Mg based on Sb1.5 normalization. 2.76 Zn 0.033 Sb 1.5 Bi 0.437 Nd 0.025 The actual composition shows that the magnesium content of the sintered single Zn doped and Zn and Nd co-doped samples is similar to that of the unsintered matrix sample in the second comparative experiment, indicating that Zn doping can reduce magnesium volatilization to a certain extent.
[0056] Figure 4The images show SEM (left) and EDS (right) images of the homogeneous Mg3(Sb,Bi)2 alloys prepared in Example 1, Comparative Experiment 1, and Comparative Experiment 2. (a) is the Mg3(Sb,Bi)2 alloy prepared in Comparative Experiment 1. 3.3 Zn 0.1 Sb 1.5 Bi 0.5 (b) Mg prepared for comparison experiment 2 3.4 Sb 1.5 Bi 0.5 (c) is the Mg prepared in Example 1. 3.28 Zn 0.1 Sb 1.5 Bi 0.5 Nd 0.02 As shown in the figure, the undoped sample exhibits obvious phase separation, and the EDS image reveals significant component segregation. The Zn-doped sample and the Zn / Nd co-doped sample both demonstrate high phase purity, with almost no component segregation or impurities. These results are consistent with the diffraction peaks observed in the XRD, and the microstructure is relatively dense with uniform elemental distribution, making it less prone to cracking, element loss, and structural stability.
[0057] Figure 5 Figure 1 shows the thermoelectric properties of the homogeneous Mg3(Sb,Bi)2 alloy prepared in Example 1 and Comparative Experiment 1 as a function of temperature. (a) Electrical conductivity, (b) Seebeck coefficient, (c) Power factor, (d) Thermal conductivity, and (e) Thermoelectric figure of merit. As shown in Figure 1(a), the single Zn-doped sample exhibits extremely low electrical conductivity, while the Zn and Nd co-doped sample shows a significant increase in conductivity, reaching nearly 600 Siemens per centimeter at room temperature. Figure 2(b) shows the drastic change in the Seebeck coefficient of the single Zn-doped sample with temperature, reflecting its low carrier concentration. In contrast, the Seebeck coefficient of the Zn and Nd co-doped sample remains stable with temperature, averaging approximately -200 μV / K. -1 This indicates that the carrier concentration is within the optimal carrier concentration range. Figure (c) shows a comparison of the power factors of the two samples. The Zn and Nd co-doped sample exhibits a good power factor, with an average value of 16.13 μW cm⁻¹ across the entire testing temperature range. -1 K -1 Figure (d) shows the comparison of thermal conductivity between the two samples. The addition of Nd will improve the thermal conductivity to a certain extent. Combined with Figures (a), (b), and (c), it can be seen that the increase in thermal conductivity is due to the increase in electronic thermal conductivity caused by the increase in carrier concentration. Figure (e) shows the comparison of thermoelectric figure of merit between the two samples. The thermoelectric figure of merit of the Zn and Nd co-doped sample is significantly higher than that of the single Zn doped sample. Its thermoelectric figure of merit shows a gradual upward trend with increasing temperature, and reaches a peak value of 1.36 at 723K.
Claims
1. A homogeneous Mg3(Sb,Bi)2 alloy prepared by a formation energy-controlled melting method, characterized in that... The general chemical formula of the homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy-controlled melting method is Mg. 3.38-x Zn x (Sb,Bi)2Nd 0.02 Where x = 0.1~0.
3.
2. The homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy-controlled melting method according to claim 1, characterized in that... At 723 K, the thermoelectric figure of merit of the homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy-controlled melting method is 1.
36.
3. The method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on the formation energy-controlled melting method as described in claim 1, characterized in that... It is done in the following steps: I. According to the general chemical formula Mg 3.38-x Zn x (Sb,Bi)2Nd 0.02 The raw materials are weighed according to the stoichiometric ratio, where x = 0.1~0.3; 2. Place the raw material in a threaded graphite crucible and wrap it with iron foil, then place it in a pointed-bottom quartz tube and vacuum seal it to obtain a sealed pointed-bottom quartz tube.
3. Place the sealed pointed-bottom quartz tube in a muffle furnace, first heat it to 550℃~590℃, then heat it to 700℃~750℃, then heat it to 1100℃~1200℃, and finally cool it to room temperature with the furnace to obtain the smelted alloy. IV. The smelted alloy is subjected to spark plasma sintering to obtain a homogeneous Mg3(Sb,Bi)2 alloy prepared by the formation energy controlled melting method.
4. The method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on the formation energy-controlled melting method according to claim 3, characterized in that... The raw materials mentioned in step one are Bi granules, Sb blocks, Mg scraps, Zn powder, and Nd blocks.
5. The method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on the formation energy-controlled melting method according to claim 4, characterized in that... The average particle size of the Bi particles is 1 mm to 3 mm; the average particle size of the Sb blocks is 3 mm to 5 mm; the average particle size of the Mg shavings is 2 mm to 3 mm; the average particle size of the Zn powder is 0.5 mm to 1 mm; and the average particle size of the Nd blocks is 3 mm to 5 mm.
6. The method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on the formation energy-controlled melting method according to claim 3, characterized in that... The purity of the raw materials mentioned in step one is 99.99%.
7. The method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on the formation energy-controlled melting method according to claim 3, characterized in that... The vacuum sealing pressure in the sealed pointed-bottom quartz tube described in step two is 3 × 10⁻⁶. -3 Pa~5×10 - 3 Pa.
8. The method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on the formation energy-controlled melting method according to claim 3, characterized in that... In step three, the temperature is first increased to 550℃~590℃ at a rate of 0.01℃ / min~10℃ / min, then increased to 700℃~750℃ at a rate of 8℃ / min~10℃ / min, then increased to 1100℃~1200℃ at a rate of 0.01℃ / min~10℃ / min, and finally cooled to room temperature with the furnace.
9. A method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on a formation energy-controlled melting method according to claim 3, characterized in that... The spark plasma sintering described in step four is carried out in the following steps: under a pressure of 30MPa~35MPa and a temperature of 750℃~800℃, the temperature is held for 2min~5min.
10. A method for preparing homogeneous Mg3(Sb,Bi)2 alloy based on a formation energy-controlled melting method according to claim 9, characterized in that... Under a pressure of 30MPa~35MPa, the temperature is increased to 700℃~750℃ in 5min~8min, and then increased to 750℃~800℃ in 2min~5min.