Method for preparing MTe nano material from Te molecular complex and application

Abstract

The invention discloses a method for preparing an MTe nano material from a Te molecular complex and application, the method comprises the following steps: (1) adding an M source into a mixed solution composed of oleic acid or oleylamine and 1-octadecene to form a cation complex solution, then carrying out preheating and vacuum degassing treatment to obtain a cation precursor solution, M being Pb or Sn; and (2) under the protection of inert atmosphere, heating the cation precursor solution to a set reaction temperature, injecting a Te source precursor, reacting for a period of time, cooling to room temperature, centrifugally separating, washing with an organic solvent, and drying to obtain the MTe nanocrystal, namely the MTe nanomaterial. The method has the advantages of mild synthesis conditions, low cost, low energy consumption, simplicity and convenience in operation, high yield and the like, and is suitable for large-scale and rapid preparation of the MTe-based nano thermoelectric material.

Description

Technical Field

[0001] The present invention relates to the technical field of energy materials, and particularly relates to a method for preparing MTe nanomaterials using a Te molecular complex and its applications. Background Art

[0002] With the continuous development of the global economy and the progress of technology, energy consumption has been increasing day by day, and environmental problems have become increasingly severe. Against this background, the development of sustainable and environmentally friendly new energy materials has become a key direction for the development of energy technology. Thermoelectric materials have received extensive attention because they can directly convert thermal energy into electrical energy through the thermoelectric effect. The performance of thermoelectric materials is mainly measured by the thermoelectric figure of merit (zT), which is defined as: zT = σS2T / κ, where σ is the electrical conductivity, S is the Seebeck coefficient, κ is the total thermal conductivity, and T is the absolute temperature. Ideal thermoelectric materials should have high electrical conductivity, high Seebeck coefficient, and low thermal conductivity. However, due to the coupling relationship among the three, it is still a great challenge to significantly improve the zT value. In the metal chalcogenide thermoelectric material system, PbTe and SnTe are two representative typical materials, both of which have the NaCl-type cubic rock salt structure (space group Fm-3m) and exhibit excellent thermoelectric properties. Specifically, the PbTe material benefits from the high Seebeck coefficient brought by its complex band structure and the low lattice thermal conductivity caused by the local centrifugal effect of Pb atoms; while the SnTe material exhibits high electrical conductivity due to a large number of intrinsic Sn vacancies, but its Seebeck coefficient is relatively low. In recent years, modulating the band structure (such as valence band convergence) to optimize the carrier transport properties has become an important strategy for improving the thermoelectric performance of PbTe- and SnTe-based materials.

[0003] At present, the synthesis of MTe (M = Pb or Sn) thermoelectric materials mainly adopts the solid-phase reaction method. Although this method has a simple process flow, it has problems such as difficult to control the grain size, high energy consumption and long synthesis cycle. Therefore, the liquid phase method has become a research hotspot because of its ability to prepare nanostructured materials under mild conditions. Nanostructures can effectively enhance phonon scattering and reduce lattice thermal conductivity, which is expected to significantly improve the thermoelectric figure of merit zT. However, existing liquid phase synthesis methods generally rely on hydrothermal or solvent thermal systems, which are carried out in closed reactors under high temperature and high pressure conditions. They are highly equipment-dependent and have limited reaction scales, making it difficult to meet the needs of practical applications. The colloidal method has attracted attention due to its advantages in crystal morphology control, particle size uniformity and controllability of reaction conditions. However, the existing colloidal synthesis methods widely use organic phosphine complexes such as tri-n-octylphosphine-tellurium (TOP-Te) or tributylphosphine-tellurium (TBP-Te) as Te sources, which are not only costly and highly toxic, but also limit their application in actual large-scale synthesis. It can be seen that the selection of Te source precursors is restricted by the above factors, and the current colloidal synthesis strategy is still difficult to achieve low-cost, sustainable and large-scale preparation of MTe nanomaterials. Therefore, it is urgent to develop an improved colloidal synthesis scheme based on non-toxic or low-toxic, highly stable Te precursors, with mild synthesis conditions, controllable morphology and suitable for scale-up production. This not only has important academic research value, but also has important significance for the application of MTe-based thermoelectric materials in the field of energy conversion. Summary of the invention

[0004] The purpose of the present invention is to provide a method and application of preparing MTe nanomaterials from Te molecular complexes, so as to realize large-scale and high-purity preparation of MTe (M = Pb or Sn) nano thermoelectric materials. The method has the advantages of simple process, low energy consumption, low cost, high yield, etc., and is particularly suitable for the large-scale preparation and application of thermoelectric materials.

[0005] In one aspect of the present invention, a method for preparing MTe nanomaterials from Te molecular complexes is provided. The method comprises the following steps:

[0006] (1) adding an M source to a mixed solution of oleic acid or oleylamine and 1-octadecene to form a cationic complex solution, and then preheating and vacuum degassing to obtain a cationic precursor solution, wherein M is Pb or Sn;

[0007] (2) Under the protection of an inert atmosphere, the cationic precursor solution is heated to a set reaction temperature, and then a Te source precursor is injected. After a period of reaction, the solution is cooled to room temperature, and then centrifuged, washed with an organic solvent, and dried to obtain MTe nanocrystals, namely the MTe nano thermoelectric material.

[0008] In addition, a method for preparing MTe nanomaterials from a Te molecular complex according to the above embodiments of the present invention may further have the following additional technical features:

[0009] In some embodiments of the present invention, in step (1), the M source is PbO or SnCl2.

[0010] In some embodiments of the present invention, in step (1), the volume ratio of oleic acid to 1-octadecene is 1:2 - 1:3, and the volume ratio of oleylamine to 1-octadecene is 3:1 - 4:1.

[0011] In some embodiments of the present invention, in step (1), the temperature for preheating the cationic complex solution is 30 - 100 °C. During the preheating process, vacuum degassing treatment is carried out, and vacuum degassing is carried out for more than 60 minutes to remove low-boiling impurities and promote the stable formation of the complex; among them, degassing is carried out for 30 minutes at 30 °C and then degassing is carried out for 30 - 60 minutes at 100 °C to obtain a stable cationic precursor solution.

[0012] In some embodiments of the present invention, in step (2), the reaction temperature is 160 - 240 °C and the reaction time is 2 - 30 minutes. Specifically, when preparing PbTe, the reaction temperature is 160 °C - 220 °C and the reaction time is 2 - 30 minutes. When preparing SnTe, the reaction temperature is 200 - 240 °C and the reaction time is 20 - 30 minutes.

[0013] In some embodiments of the present invention, in step (2), the molar ratio of M in the M source to Te in the Te source is 0.96 - 1:1.

[0014] In some embodiments of the present invention, in step (2), the Te source precursor is a Te molecular complex solution formed by dissolving tellurium powder in a mixed solution composed of ethylenediamine and ethanethiol, and the concentration of the Te source precursor is 0.6 - 0.65 mol / L. The entire dissolution process lasts for 1 - 3 days to ensure the complex stability and reaction activity of the Te source.

[0015] In some embodiments of the present invention, the volume ratio of ethylenediamine to ethanethiol is 16.5:6.5 - 10.

[0016] In some embodiments of the present invention, in step (2), the washing is carried out using a mixed system of n-hexane and absolute ethanol; the centrifugation speed is 6000 - 9000 rpm, each time lasting for 5 - 10 minutes; the drying is carried out by vacuum drying, the drying temperature is 60 - 80 °C, and the drying time is 3 - 8 hours.

[0017] In some embodiments of the present invention, in step (2), the MTe nanocrystals have a NaCl-type cubic rock-salt structure.

[0018] In another aspect of the present invention, the present invention provides a thermoelectric material. According to an embodiment of the present invention, it includes the MTe nanomaterial prepared by the method for preparing MTe nanomaterial using the Te molecular complex described above.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The present invention provides a new strategy for synthesizing nanocrystals based on Te molecular complexes. Through the stable release behavior of Te molecular complexes in the reaction, the supply rate of Te source and the reaction uniformity are effectively regulated, optimizing the nucleation and growth processes of MTe crystals from the aspects of thermodynamics and kinetics, thereby realizing the controllable synthesis of grain size, morphology, and structural purity, which is significantly superior to the traditional synthesis system. Compared with the traditional solid-phase vacuum melting method, the precise regulation ability of grain size and phase composition is significantly improved. By introducing a complexed Te source solution, surface oxidation and the formation of long-chain organic residues can be inhibited at a lower reaction temperature, thereby obtaining pure and stable MTe nanomaterials, breaking through the technical bottlenecks in phase control and microscopic regulation of traditional methods.

[0021] (2) The present invention combines Te molecular complexes with a low-temperature rapid injection synthesis strategy, effectively overcoming the limitations of hydrothermal and solvothermal methods. In comparison, this method does not rely on high-pressure reaction vessels, reducing equipment investment and operation complexity, and significantly reducing the by-product pollution caused by solvent decomposition or residues. The reaction conditions of the method of the present invention are mild, the reaction time is short, and the product yield is high, etc., with better reproducibility and scalability, providing a feasible and efficient solution for the large-scale synthesis of MTe materials.

[0022] (3) Compared with the existing colloidal synthesis methods based on TOP-Te or TBP-Te precursors, the present invention has obvious advantages in terms of cost, safety, and large-scale application. Traditional phosphine-based Te precursors have problems such as high toxicity, high price, cumbersome synthesis, low yield, and often require subsequent annealing to obtain the main phase structure, greatly restricting their promotion in industrial scenarios. In contrast, the present invention uses a cheap and stable complex system composed of ethylenediamine and ethanethiol to form Te molecular complexes, the cost of which is about one-tenth of that of TOP-Te precursors, significantly improving the synthesis efficiency. The reaction yield exceeds 95%, and the product crystallinity is higher, significantly enhancing the availability and application promotion potential of the material. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the experimental process for preparing MTe nanomaterials using a Te molecular complex according to the present invention;

[0024] Figure 2XRD patterns of PbTe nanomaterials and SnTe nanomaterials prepared in Example 1 and Example 6 of the present invention;

[0025] Figure 3 XRD patterns of PbTe nanomaterials prepared in Examples 1-5 and Comparative Example 1 of the present invention;

[0026] Figure 4 XRD patterns of SnTe nanomaterials prepared in Example 6 and Comparative Example 2 of the present invention;

[0027] Figure 5 SEM images of PbTe-based nanothermoelectric materials prepared in Example 1(a), Example 2(b), Example 4(c) and Comparative Example 1(d) of the present invention;

[0028] Figure 6 SEM images of SnTe nanomaterials with different magnifications prepared in Example 6(a) and Comparative Example 2(b) of the present invention;

[0029] Figure 7 Electrical property curves of the bulk materials obtained by hot pressing and densifying the PbTe-based nanothermoelectric materials prepared in Example 1 and Comparative Example 1 of the present invention: a) Electrical conductivity, b) Seebeck coefficient;

[0030] Figure 8 Electrical property curves of the bulk materials obtained by hot pressing and densifying the SnTe-based nanothermoelectric materials prepared in Example 6 and Comparative Example 2 of the present invention: a) Electrical conductivity, b) Seebeck coefficient. Detailed implementation manners

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] Example 1

[0033] A method for preparing PbTe nanomaterials using a Te molecular complex, comprising the following steps:

[0034] (1) Preparation of cationic and anionic precursors

[0035] a. Large-scale preparation of anionic Te precursor: At room temperature, 15 mmol of Te powder was placed in a glass container with 23 mL of molecular ligand (ink) in a glove box, including 16.5 mL of ethylenediamine and 6.5 mL of ethanethiol. Magnetic stirring continued for 2 days until completely dissolved, and the solution became a dark red solution. Finally, a Te molecular complex solution with a concentration of 0.65 mol / L was prepared as the anionic precursor.

[0036] b. Preparation of cationic precursor: 12 mmol of PbO powder was accurately weighed with an analytical balance and placed in a 500 mL three-necked flask. Then, 60 mL of 1-octadecene and 30 mL of oleic acid were successively injected into it, and magnetic stirring was carried out at room temperature.

[0037] (2) Preparation of PbTe nanomaterials

[0038] c. First, the cationic precursor in step (1)b was vacuum degassed at room temperature and 100 °C for 30 min respectively to remove the low-boiling impurities therein, and then nitrogen was introduced and the temperature was rapidly raised. During this process, the solution changed from turbid milky white to brown at about 130 °C. When the temperature was raised to 180 °C, 18.4 mL of the pre-prepared 0.65 mol / L Te molecular complex solution in step (1)a was injected according to the molar ratio of Pb to Te of 1:1. After the injection was completed, timing started. After reacting for 5 min, it was quickly cooled to room temperature in a water bath.

[0039] d. The cooled solution was centrifugally washed with n-hexane as the dispersant and absolute ethanol as the precipitant. The volume ratio of n-hexane to absolute ethanol was 1:1, and centrifugal washing was carried out 3 times at a rotation speed of 9000 rpm for 5 min each time. The obtained product was transferred to a vacuum drying oven and dried at 60 °C for 4 h. Finally, about 3.8 g of PbTe nanometer powder was obtained, and the yield was close to 95% of the theoretical yield.

[0040] Example 2

[0041] A method for preparing PbTe nanomaterials using a Te molecular complex. The difference between this example and Example 1 is that in step c of Example 1, when the temperature rose to 160 °C, 18.4 mL of the pre-prepared 0.65 mol / L Te molecular complex solution was injected into the cationic precursor solution containing Pb according to the molar ratio of Pb to Te of 1:1. After the injection was completed, timing started. After reacting for 5 min, it was cooled to room temperature in a water bath. Example 2 only has a difference in the reaction temperature, and the other steps are the same as those in Example 1.

[0042] Example 3

[0043] A method for preparing PbTe nanomaterials using a Te molecular complex. The difference between this example and Example 1 is that in step c of Example 1, when the temperature rises to 200 °C, 18.4 mL of a pre-prepared 0.65 mol / L Te molecular complex solution is injected into the cationic precursor solution containing Pb according to a molar ratio of Pb to Te of 1:1. After the injection is completed, timing starts, and the reaction proceeds for 5 minutes. After the reaction, it is cooled to room temperature in a water bath. Example 3 only differs in the reaction temperature, and the remaining steps are the same as those in Example 1.

[0044] Example 4

[0045] A method for preparing PbTe nanomaterials using a Te molecular complex. The difference between this example and Example 1 is that in step c of Example 1, when the temperature rises to 180 °C, 18.4 mL of a pre-prepared 0.65 mol / L Te molecular complex solution is injected into the cationic precursor solution containing Pb according to a molar ratio of Pb to Te of 1:1. After the injection is completed, timing starts, and the reaction proceeds for 2 minutes. After the reaction, it is cooled to room temperature in a water bath. Example 4 only differs in the reaction time, and the remaining steps are the same as those in Example 1.

[0046] Example 5

[0047] A method for preparing PbTe nanomaterials using a Te molecular complex. The difference between this example and Example 1 is that in step c of Example 1, when the temperature rises to 180 °C, 18.4 mL of a pre-prepared 0.65 mol / L Te molecular complex solution is injected into the cationic precursor solution containing Pb according to a molar ratio of Pb to Te of 1:1. After the injection is completed, timing starts, and the reaction proceeds for 10 minutes. After the reaction, it is cooled to room temperature in a water bath. Example 5 only differs in the reaction time, and the remaining steps are the same as those in Example 1.

[0048] Comparative Example 1

[0049] A method for preparing PbTe nanomaterials by a colloid method, which is characterized by including the following steps:

[0050] (1) Preparation of cationic and anionic precursors

[0051] a. Large-scale preparation of anionic Te precursor: At room temperature, dissolve 7.656 g of tellurium grains in 60 mL of tri-n-octylphosphine (TOP) in a glove box, and magnetically stir for more than one week in the glove box to prepare a clear light yellow TOP-Te precursor solution with a concentration of 1 mol / L.

[0052] b. Preparation of cationic precursor: Weigh 12 mmol of PbO powder accurately with an analytical balance and place it in a 500 mL three-necked flask. Subsequently, add a mixed solution of 90 mL of 1-octadecene and 15 mL of oleic acid, and stir magnetically at room temperature.

[0053] (2) Preparation of PbTe nanomaterials by traditional colloid method

[0054] c. First, evacuate and degas the mixed solution in 1b at room temperature and 100 °C for 30 min each to remove the low-boiling impurities therein, then introduce nitrogen and quickly raise the temperature. When the temperature rises to 190 °C, inject 12 mL of 1 mol / L TOP-Te precursor solution prepared in step 1a according to the molar ratio of Pb to Te of 1:1. The reaction mixture is maintained at 180 °C for 10 min, and after the reaction, it is cooled to room temperature in a water bath.

[0055] d. Centrifuge and wash the cooled solution three times with n-hexane and absolute ethanol at a rotation speed of 9000 rpm for 5 min each time. Transfer the obtained product to a vacuum drying oven and dry it under vacuum at 60 °C for 4 h to finally prepare PbTe nanocrystals.

[0056] Example 6

[0057] A method for preparing SnTe nanomaterials using a Te molecular complex, comprising the following steps:

[0058] (1) Preparation of anionic and cationic precursors

[0059] a. Preparation of anionic Te precursor (Te molecular complex): The steps are the same as those in the example of PbTe nanomaterial preparation.

[0060] b. Preparation of cationic precursor: Weigh 12 mmol of anhydrous SnCl2 accurately with an analytical balance and place it in a 500 mL three-necked flask. Inject 96 mL of 1-octadecene and 24 mL of oleic acid into it successively, and stir magnetically at room temperature.

[0061] (2) Preparation of SnTe nanomaterials

[0062] c. First, evacuate and degas the cationic precursor in step (1)b at room temperature and 100 °C for 30 min each to remove the low-boiling impurities therein, then introduce nitrogen and quickly raise the temperature. During this process, the solution changes from turbid milky white to brown transparent solution at about 130 °C. When the temperature rises to 160 °C, inject 18.4 mL of 0.65 mol / L Te molecular complex solution prepared in step (1)a according to the molar ratio of Sn to Te of 1:1. After injection, start timing when the solution rises to 240 °C, react for 30 min, and after the reaction, cool it to room temperature in a water bath.

[0063] d. Use n - hexane as the dispersant and absolute ethanol as the precipitant to centrifuge and wash the cooled solution. The volume ratio of n - hexane to absolute ethanol is 1:1. Centrifuge and wash 3 times at a rotation speed of 9000 rpm for 5 minutes each time. Transfer the obtained product to a vacuum drying oven and dry at 60 °C for 4 hours to finally obtain SnTe nano - powder.

[0064] Example 7

[0065] A method for preparing SnTe nano - materials using a Te molecular complex. The difference between this example and Example 6 is that in step c of Example 6, when the temperature reaches 160 °C, inject the Te - source precursor solution in a ratio of 1:1 and then raise the temperature to 220 °C and start the reaction timing for 30 minutes. Example 7 only has a difference in the reaction temperature, and the other steps are the same as those in Example 6.

[0066] Comparative Example 2

[0067] A method for preparing SnTe nano - materials by a hydrothermal method, which is characterized by including the following steps:

[0068] a. Add 30 mL of deionized water to a 50 - mL beaker, add 1.2 g of granular NaOH thereto, stir for 10 minutes under the condition of a stirring speed of 600 r·min -1 , then add 3 mmol of SnCl₂·2H₂O, continue to stir for 10 minutes, then add 0.9 g of NaBH₄ reducing agent, stir for 10 minutes, and then add 3 mmol of TeO₂, stir for 15 minutes until a uniform reaction precursor solution is formed. Transfer the above - stirred reaction solution to a high - pressure reaction kettle with a polytetrafluoroethylene liner and heat and react at a constant temperature of 160 °C for 36 hours.

[0069] b. After the reaction is completed, naturally cool to room temperature, centrifuge and wash the obtained product 5 times successively with deionized water and absolute ethanol. The rotation speed for each centrifugation is 5000 rpm and the time is 3 minutes. The washed product is treated in a vacuum drying oven and dried at 60 °C for 4 hours to finally obtain the SnTe nano - material powder.

[0070] As Figure 1 shown, it is a schematic diagram of the experimental process for synthesizing MTe nano - materials based on Te molecular complexes according to the present invention. Under the protection of an inert atmosphere (nitrogen), inject the pre - prepared Te - source complex solution (the specific structural formula is marked in the figure) into the container containing metal M 2+In the ligand solution of the cationic precursor, a reaction system is formed. By precisely controlling the reaction temperature and time, a stable dispersion solution of MTe nanocrystals is formed within the system. After the reaction, the nanocrystals are purified by centrifugation, and the obtained product is dispersed in hexane for phase exchange to further remove residual organic ligands. Finally, the target MTe nanocrystal powder is obtained by vacuum drying, and the overall yield can reach over 95%.

[0071] To verify the phase purity and crystal structure of the synthesized materials, a X-Pert PRO MPD type X-ray diffractometer (XRD) produced by PANalytical of the Netherlands was used to perform phase characterization on the samples. As Figure 2 shown, the XRD patterns of the PbTe and SnTe sample powders obtained in Example 1 and Example 6 are shown. They are all completely matched with the corresponding standard cards, and both are face-centered cubic structures (FCC) with a space group of Fm-3m. The detailed XRD pattern of the PbTe sample. As Figure 3 shown, the XRD diffraction peaks of PbTe obtained in Examples 1 to 5 are all completely matched with the standard PbTe diffraction card (PDF#03-065-0324); as Figure 4 shown, the XRD pattern of the SnTe nanomaterial sample prepared in Example 6 is also completely matched with the standard SnTe card (PDF#00-046-1210). The above results indicate that the method for synthesizing Te molecular complexes described in the present invention can stably obtain pure-phase PbTe and SnTe nanocrystals, and no obvious impurity phases are observed, verifying the significant advantages of this method in terms of composition control and phase purity.

[0072] A high-resolution field emission scanning electron microscope (Hitachi Regulus8230) produced by Hitachi of Japan was used to analyze the microstructure and size distribution of the prepared PbTe and SnTe nanomaterials. As Figure 5 and Figure 6 shown, the morphologies of the PbTe and SnTe nanomaterials synthesized by the method of the present invention are concentrated in the range of dozens to several micrometers, and different examples have different particle sizes. It can be seen that the size of the particles can be effectively regulated by controlling the reaction temperature or time.

[0073] The as-prepared PbTe (Example 1 and Comparative Example 1) and SnTe (Example 6 and Comparative Example 2) nanopowders were vacuum-dried and then annealed in a tube furnace under a mixed gas of N2 + 5% H2. The specific process conditions were as follows: the heating process from room temperature to 500 °C was set to take 1 h; the SnTe sample was annealed at 600 °C for 2 h, and the heating time was set to 1.5 h. The annealed samples were ground in an agate mortar in a glove box and then poured into a graphite mold with an inner diameter of 10 mm lined with 0.20 mm carbon paper. It was sintered using a commercial hot pressing system under nitrogen protection. The hot pressing conditions were: pressure 70 MPa, temperature 500 °C, holding pressure and temperature for 10 min. The finally obtained circular dense blocks had a size of 10 mm in diameter and 1.5 mm in thickness. The density measurement results showed that they all reached the range of 92% - 95% of the theoretical density of the corresponding MTe (M = Pb, Sn), indicating a high degree of powder densification, which was suitable for subsequent thermoelectric property testing and device processing, that is, it could be used as a thermoelectric material.

[0074] The electrical properties of the hot-pressed and densified (Example 1 and Comparative Example 1) and SnTe (Example 6 and Comparative Example 2) bulk samples were characterized. Using the Seebeck coefficient / resistance test system LSR-3 produced by LINSEIS Company in Germany, the temperature-dependent tests of the electrical conductivity (σ) and Seebeck coefficient (S) of the PbTe and SnTe bulk samples were carried out.

[0075] Figure 7 The comparison of the electrical properties of the PbTe nanomaterials synthesized by the Te molecular complex method (Example 1) and the traditional TOP-Te method (Comparative Example 1) described in the present invention is shown. Figure 7 Figure a shows that in the low-temperature region (300 - 500 K), the electrical conductivity of the sample in Example 1 was significantly higher than that in Comparative Example 1, indicating that the method of the present invention has a high carrier mobility without using expensive organophosphorus precursors. Figure 7 Figure b shows that both samples exhibited typical p - n type polarity conversion behavior in the entire test temperature range (room temperature to 827 K), and the Seebeck coefficient changed from positive to negative at about 500 K, which was consistent with the intrinsic bipolar conduction mechanism of the PbTe material.

[0076] Figure 8 It is a comparison diagram of the electrical properties of Example 6 and Comparative Example 2 of the SnTe material. Due to the intrinsically high Sn vacancy concentration in the SnTe material, both samples showed high electrical conductivity in the entire test range from room temperature to 840 K Figure 8a). Its conductivity shows a monotonically decreasing trend with the increase of temperature, reflecting the typical high carrier concentration transport behavior caused by the enhanced carrier scattering under thermal excitation conditions in this system. At the same time, due to the excessively high carrier concentration, the Seebeck coefficient of the SnTe sample is generally low and shows a slow upward trend ( Figure 8 b). However, the sample prepared in Example 6 exhibits a higher Seebeck coefficient throughout the test temperature range, indicating that its Sn vacancy concentration is relatively low, thus achieving more optimized carrier concentration control. Subsequently, its power factor can be further optimized through energy band regulation or co-doping methods to achieve better thermoelectric performance.

[0077] The above results show that the PbTe and SnTe nano-thermoelectric materials prepared by the Te molecular complex method described in the present invention exhibit excellent thermoelectric transport behavior and regulation potential while maintaining good electrical conductivity, providing strong support for their high-performance applications in medium-temperature thermoelectric devices.

[0078] The above content is only an example and illustration of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing MTe nanomaterials using a Te molecular complex, characterized in that, It includes the following steps: (1) Add the M source into a mixed solution composed of oleic acid or oleylamine and 1-octadecene to form a cationic complex solution, and then perform preheating and vacuum degassing treatments to obtain a cationic precursor solution, where M is Pb or Sn; (2) Under the protection of an inert atmosphere, after heating the cationic precursor solution to a set reaction temperature, inject the Te source precursor. After reacting for a period of time, cool it to room temperature, and obtain MTe nanocrystals through centrifugal separation, organic solvent washing, and drying, which are the MTe nanomaterials.

2. The method for preparing MTe nanomaterials using a Te molecular complex according to claim 1, characterized in that: In step (1), the M source is PbO or SnCl2, the volume ratio of oleic acid to 1-octadecene is 1:2 - 1:3, and the volume ratio of oleylamine to 1-octadecene is 3:1 - 4:

1.

3. The method for preparing MTe nanomaterials using a Te molecular complex according to claim 1, characterized in that: In step (1), the preheating temperature of the cationic complex solution is 30 - 100 °C, and vacuum degassing treatment is performed during the preheating process, where degassing is carried out for 30 min at 30 °C and then for 30 - 60 min at 100 °C.

4. The method for preparing MTe nanomaterials from a Te molecular complex according to claim 1, wherein: In step (2), the reaction temperature is 160 - 240 °C, and the reaction time is 2 - 30 min.

5. The method for preparing MTe nanomaterials using a Te molecular complex according to claim 1, characterized in that: In step (2), the molar ratio of M in the M source to Te in the Te source is 0.96 - 1:

1.

6. The method for preparing MTe nanomaterials from a Te molecular complex according to claim 1, characterized in that: In step (2), the Te source precursor is a Te molecular complex solution formed by dissolving tellurium powder in a mixed solution composed of ethylenediamine and ethanethiol, and the concentration of the Te source precursor is 0.6 - 0.65 mol / L.

7. The method for preparing MTe nanomaterials using a Te molecular complex according to claim 6, wherein: The volume ratio of ethylenediamine to ethanethiol is 16.5:6.5 - 10.

8. A method for preparing MTe nanomaterials using a Te molecular complex according to claim 1, characterized in that: In step (2), the washing is carried out using a mixed system of n-hexane and absolute ethanol; the centrifugal speed is 6000 - 9000 rpm, each time lasting for 5 - 10 min; the drying is carried out by vacuum drying, the drying temperature is 60 - 80 °C, and the drying time is 3 - 8 h.

9. The method for preparing MTe nanomaterials from a Te molecular complex according to claim 1, wherein: In step (2), the MTe nanocrystals have an NaCl-type cubic rock salt structure.

10. A thermoelectric material, characterized in that: It includes the MTe nanomaterials prepared by the method for preparing MTe nanomaterials from the Te molecular complex as described in any one of claims 1 - 9.

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