Synthesis And Properties Of Thermoelectric Materials Based On Ternary Chalcogenide Compounds

Ternary chalcogenide semiconductor materials play a very important role in basic research and practical applications due to their high efficiency,adjustable electrical and thermal transport properties,high element abundance,and low toxicity.The search for a simple and efficient synthetic method that can tailor their crystal components and control their morphology to change their bandgaps to prepare such semiconductor material has received increasing attention from scientists.The Cu-Sb-S system,a ternary semiconductor material system composed of three elements that are abundantly stored on earth,having a bandgap that changes with the component and morphology of Cu-Sb-S nanocrystals is an excellent alternative material for constructing thermoelectric and optoelectronic devices and has great potential value.At the same time,ZnIn₂Se₄ is considered to be a promising N-type thermoelectric material because of its low intrinsic lattice thermal conductivity.It was found that the key to achieving high-performance thermoelectric materials is their high electrical conductivity,high Seebeck coefficient,and low thermal conductivity of the lattice.These properties are affected by the preparation process and structural properties of the material itself.Therefore,the specific research in this thesis as follows:?1?A new low-cost and efficient method for the preparation of nanomaterials of the Cu-Sb-S system was investigated,and the effects of reaction temperature,reaction time,and precursor stoichiometry ratios on the synthesis of Cu-Sb-S system were deeply studied.As a result,single-phase Cu₃SbS₄ and Cu₁₂Sb₄S₁₃3 were successfully synthesized;and the mechanism of solvent thermal synthesis of nanosized particles of pure-phase Cu-Sb-S system was analyzed.These ternary sulfide nanoparticles form a hollow spherical structure through certain bonding,which is stable at room temperature and is not affected by vibrations such as ultrasound.Scanning electronic microscopy results show that the spheres have uniform micron size and most of them have a surface rupture.Hall and Seebeck coefficient tests showed that the Cu₃SbS₄ and Cu₁₂Sb₄S₁₃finally synthesized were both P-type semiconductors.?2?The intrinsic thermoelectric properties of the as-prepared Cu₃SbS₄nanocrystals were characterized in the test range of 300-625 K.The Cu₃SbS₄synthesized by this method has a very low thermal conductivity of less than 0.5 W/m·K in the whole test range.A very low lattice thermal conductivity of 0.27 W/m·K is obtained at a temperature of 625 K,which is mainly attributed to its nanoscale grains which can significantly increase the interfacial scattering of phonons by the material itself,thus effectively reducing the lattice thermal conductivity.At a temperature of 625K,the intrinsic Cu₃SbS₄ achieves a ZT of 0.08,which is a very promising thermoelectric material.?3?The structure,morphology,and thermoelectric properties of ZnIn₂Se₄thermoelectric material prepared by the melting method were studied.Intrinsic ZnIn₂Se₄is an N-type semiconductor with a low carrier concentration of 1.8×10¹⁸ cm^-3 and a low lattice thermal conductivity of 0.9 W/m·K at 850 K,leading to a maximum value of 0.24 for the ZT of intrinsic ZnIn₂Se₄.In summary,by analyzing the structure,morphology,and thermoelectric properties of intrinsic Cu₃SbS₄ and intrinsic ZnIn₂Se₄,it is proved that both Cu₃SbS₄and intrinsic ZnIn₂Se₄ are potential thermoelectric materials of ternary sulfur compounds,which will lay a solid foundation for the development of low-cost and high-performance thermoelectric devices in the future.