Preparation method and application of Ag8SnSe6 nanocrystal

Abstract

The invention relates to the technical field of nanocrystalline materials, and discloses a preparation method and application of Ag8SnSe6 nanocrystalline, and the preparation method of the Ag8SnSe6 nanocrystalline comprises the following steps: adding Se, oleylamine and dodecanethiol into a container I for ultrasonic treatment to obtain a Se precursor; agNO3, SnCl4. 5H2O, Se, oleylamine and oleic acid are added into a second container, vacuumizing and primary stirring are conducted, then the temperature is increased to 80 DEG C, vacuumizing and secondary stirring are conducted, low dimension of the material structure is achieved, and therefore the freedom degree of decoupling electric heat transportation is increased; the quantum confinement effect of the nano material is utilized to increase the state density of the Fermi surface, so that the Seebeck coefficient of the material is remarkably enhanced, and a relatively high power factor is obtained; meanwhile, nanocrystallization of the material can generate a dimension and size limiting effect and an interface scattering effect on phonon transmission, so that the heat conductivity is reduced; therefore, the thermoelectric performance of the material is effectively improved due to low dimension of the material structure.

Description

Technical Field

[0001] The present invention relates to the technical field of nanocrystalline materials, and in particular to a preparation method and application of Ag8SnSe6 nanocrystals. Background Art

[0002] As a cutting-edge new energy material, thermoelectric conversion materials can convert heat energy into electrical energy, thereby improving fuel efficiency, improving environmental pollution, and achieving energy renewable. In addition, thermoelectric conversion technology has important application prospects in the fields of cooling of small electronic devices such as semiconductor chips, temperature control of aerospace vehicles and related components.

[0003] The most direct strategy to improve the thermoelectric performance of materials is to increase the power factor and reduce the lattice thermal conductivity. In practical applications, reducing the lattice thermal conductivity is mainly achieved by introducing defect structures in the matrix. However, the introduction of defect structures will not only scatter phonons, but also scatter carriers in the material, thereby affecting the electrical properties, resulting in the limitation of the ZT value improvement of most materials. The development of intrinsic low thermal conductivity materials can solve this problem well. The lower intrinsic thermal conductivity in the material can avoid the carrier scattering caused by the introduction of defect structures, thereby focusing on the improvement of electrical transport performance, while taking into account the reserve abundance and production cost of the material.

[0004] Among them, Ag8SnSe6 is one of the thermoelectric materials with the lowest sound velocity and thermal conductivity. It is also environmentally friendly and has high element abundance, which means it has broad space for future commercial applications. However, Ag8SnSe6 currently has a low carrier concentration and poor electrical transport performance, especially its thermoelectric performance near room temperature is not ideal, and its ZTave value is low. In addition, the multi-scale (low-dimensional) structural regulation of Ag8SnSe6 materials is still blank. The currently prepared materials have large particle sizes and difficult decoupling regulation of electrical and thermal transport. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a preparation method and application of Ag8SnSe6 nanocrystals.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing Ag8SnSe6 nanocrystals comprises the following steps:

[0008] Step 1: Add Se, oleylamine and dodecanethiol into container 1 and perform ultrasonic treatment to obtain a Se precursor;

[0009] Step 2: Add AgNO3, SnCl4.5H2O, Se, oleylamine and oleic acid into container 2, evacuate and stir for the first time, then heat to 80°C, evacuate and stir again, then introduce nitrogen into container 2, heat to 220°C, and add the Se precursor obtained in step 1 to fully react;

[0010] Step 3: After the reactant obtained in the second container of step 2 is naturally cooled to room temperature, it is washed twice with n-hexane and ethanol to obtain nanocrystals;

[0011] Step 4: Add ammonium thiocyanate to acetone to obtain an ammonium thiocyanate solution. Wash the nanocrystals prepared in step 2 once with the prepared ammonium thiocyanate solution, then wash once with ethanol, and finally put them into a vacuum drying oven and dry them overnight to obtain the Ag8SnSe6 nanocrystals.

[0012] Preferably, in step 1, the concentration of oleylamine is 80%-90%; in step 1, the duration of ultrasonic treatment is 30 minutes.

[0013] Preferably, in step 2, the initial stirring time of vacuuming is 30 minutes; the time of vacuuming and stirring again after heating to 80° C. is 1 hour; and the reaction time after adding the Se precursor obtained in step 1 is 30 minutes.

[0014] Preferably, in step 4, the temperature in the drying oven is 80°C.

[0015] The Ag8SnSe6 nanocrystals prepared by the above-mentioned method for preparing Ag8SnSe6 nanocrystals are applied in the thermoelectric field.

[0016] The beneficial effects of the present invention are:

[0017] 1. The present invention successfully synthesizes Ag8SnSe6 nanocrystals through a colloidal method, realizes the low-dimensionality of the material structure, thereby increasing the degree of freedom of decoupled electrothermal transport; utilizes the quantum confinement effect of nanomaterials to increase the state density of the Fermi surface, thereby significantly enhancing the Seebeck coefficient of the material, thereby obtaining a higher power factor; at the same time, the nano-material will also produce dimensional and size restriction effects and interface scattering effects on phonon transmission, thereby reducing thermal conductivity; therefore, the low-dimensionality of the material structure effectively improves its thermoelectric performance.

[0018] 2. The present invention utilizes a structural low-dimensionalization method to effectively increase the state density near the Fermi level, increase the carrier concentration, and effectively improve the electrical conductivity of the material.

[0019] 3. The present invention uses ammonium thiocyanate solution to perform phase exchange to remove molecular chains; the grain size of the Ag8SnSe6 nanocrystals prepared by the present invention is 11-15nm; the ZT value of the Ag8SnSe6 nanocrystals prepared by the present invention reaches 0.5. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The preparation flow chart of Ag8SnSe6 nanocrystals;

[0021] Figure 2 TEM images and particle size diagrams of Ag8SnSe6 nanocrystals synthesized at different temperatures;

[0022] Figure 3 XRD patterns of Ag8SnSe6 nanocrystals synthesized at different temperatures;

[0023] Figure 4 HRTEM and EELS images of Ag8SnSe6 nanocrystals;

[0024] Figure 5 This is the XPS image of Ag8SnSe6 nanocrystals;

[0025] Figure 6 The temperature-dependent XRD pattern of Ag8SnSe6 bulk after hot pressing;

[0026] Figure 7 The cross-sectional SEM image and EDX spectrum of Ag8SnSe6 bulk;

[0027] Figure 8 The thermoelectric performance diagram of Ag8SnSe6;

[0028] Fig. 9 This is the thermogravimetric analysis diagram of Ag8SnSe6;

[0029] Fig.10 This is the mechanical hardness diagram of Ag8SnSe6. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0031] Example: Take the preparation of 1mmol of Ag8SnSe6 as an example;

[0032] 1 mmol of Se, 6 ml of 80%-90% oleylamine and 6 ml of dodecanethiol were added to a 30 ml centrifuge tube and ultrasonicated for 30 min to obtain a Se precursor;

[0033] 8mmol of AgNO3, 1mmol of SnCl4.5H2O, 1mmol of Se, 100ml of oleylamine and 16mL of oleic acid were added into a 250ml three-necked flask, and the mixture was stirred for 30min under vacuum for the first time. Then, the mixture was heated to 80℃ and stirred for 1h under vacuum again. Then, nitrogen was introduced into the three-necked flask and the mixture was heated to 220℃. The above-mentioned Se precursor was injected and reacted for 30min. After being cooled to room temperature naturally, the mixture was washed twice with n-hexane and ethanol to obtain nanocrystals.

[0034] 0.07612 g of ammonium thiocyanate was added to 20 ml of acetone to obtain an ammonium thiocyanate solution. The above-mentioned nanocrystals were washed once with the prepared ammonium thiocyanate solution, and then washed once with ethanol. Finally, they were placed in a vacuum drying oven and dried at 80°C overnight to obtain 1 mmol of the above-mentioned Ag8SnSe6 nanocrystals.

[0035] The morphology and grain size of Ag8SnSe6 nanocrystals prepared by controlling the synthesis temperature in the above invention illustrate that the particle size distribution of the nanocrystals prepared when the reaction temperature is 220°C is uniform ( Figure 2 ), the X-ray diffraction (XRD) peaks of the nanocrystals prepared at a reaction temperature of 220°C are completely consistent with the standard card of cubic phase Ag8SnSe6 nanocrystals ( Figure 3 ), indicating that the sample is pure phase and does not contain other impurities. In addition, the high-resolution transmission electron microscopy (HRTEM) and EELS images of the nanocrystals show the corresponding unit cell spacing, which is consistent with Ag8SnSe6, and the Ag, Sn and Se elements are evenly distributed ( Figure 4 ). The X-ray photoelectron spectroscopy (XPS) graph shows the characteristic peaks of Ag 3d, Sn 3d and Se 2p, further proving the successful synthesis of Ag8SnSe6 nanocrystals ( Figure 5 ).

[0036] The X-ray diffraction (XRD) peaks of the bulk sample after hot pressing are completely consistent with the standard card of orthorhombic Ag8SnSe6 nanocrystals, indicating that the sample is pure phase, does not contain other impurities, and undergoes phase transition between 348K and 373K, which is consistent with the phase transition law of the material ( Figure 6 ). The corresponding element mapping images and energy spectrum analysis can be observed through scanning electron microscopy (SEM), indicating that the Ag, Sn and Se elements in the block are uniformly distributed ( Figure 7 The electrical conductivity, Seebeck coefficient, thermal conductivity and other performance parameters of the Ag8SnSe6 bulk sample were tested and its ZT value was calculated. The ZT value can reach 0.5 at 723K ( Figure 8 In addition, the thermogravimetric analysis results show that the sample has good thermal stability ( Fig. 9). Finally, the mechanical hardness of the sample was tested, and the results showed that the sample had good mechanical hardness, indicating that the material has great potential for application in future commercial applications ( Fig.10 ).

[0037] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing Ag8SnSe6 nanocrystals, characterized in that: The following steps are involved: Step 1: Se, oleylamine and dodecanethiol are added into container 1 and subjected to ultrasonic treatment to obtain a Se precursor; Step 2: Add AgNO3, SnCl4.5H2O, Se, oleylamine and oleic acid into container 2, evacuate and stir for the first time, then heat to 80°C, evacuate and stir again, then introduce nitrogen into container 2, heat to 220°C, and add the Se precursor obtained in step 1 to fully react; Step 3: After the reactant obtained in the second container of step 2 is naturally cooled to room temperature, it is washed twice with n-hexane and ethanol to obtain nanocrystals; Step 4: Add ammonium thiocyanate to acetone to obtain an ammonium thiocyanate solution. Wash the nanocrystals prepared in step 2 once with the prepared ammonium thiocyanate solution, then wash once with ethanol, and finally put them into a vacuum drying oven and dry them overnight to obtain the Ag8SnSe6 nanocrystals.

2. The method for preparing Ag8SnSe6 nanocrystals according to claim 1, characterized in that: In step 1, the concentration of oleylamine is 80%-90%; in step 1, the duration of ultrasonic treatment is 30 minutes.

3. The method for preparing Ag8SnSe6 nanocrystals according to claim 1, characterized in that: In step 2, the initial stirring time of vacuuming is 30 minutes; the time of vacuuming and stirring again after heating to 80°C is 1 hour; and the reaction time after adding the Se precursor obtained in step 1 is 30 minutes.

4. The method for preparing Ag8SnSe6 nanocrystals according to claim 1, characterized in that: In step 4, the temperature in the drying oven is 80°C.

5. Application of the Ag8SnSe6 nanocrystals prepared by the method for preparing Ag8SnSe6 nanocrystals as described in any one of claims 1 to 4 in the field of thermoelectricity.

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