Synergetic Optimization Of Band Structure And Microstructure For High-Performance SnTe-Based Thermoelectric Materials

Sustainable energy development strategies such as carbon neutrality and zero carbon emission are the new trends in international energy development.SnTe compounds are one of the most promising representatives in the field of medium-temperature thermoelectric materials.However,the intrinsic SnTe thermoelectric properties are low（ZT≈0.4 at 873 K）due to the presence of a large number of intrinsic Sn vacancies,a large light-heavy band energy difference,and a high lattice thermal conductivity.This paper aims to optimize the thermoelectric properties of SnTe,mainly through carrier engineering,optimization of the energy band structure and multiscale microstructure tuning to improve the electrothermal transport properties and analyze the mechanism.The main research contents and conclusions are as follows:（1）Using P-type SnTe as the research object,the conductivity and Seebeck coefficient are effectively decoupled by alloying W with SnTe in a new way,resulting in a substantial improvement of the power factor in the full test temperature domain.Specifically,the gap defects produced by alloying W with SnTe can effectively reduce the formation energy of intrinsic Sn vacancy defects,thereby increasing the hole carrier concentration and overall conductivity.Meanwhile,W alloying leads to valence band convergence and resonance energy level formation thus enhancing the low-temperature Seebeck coefficient,and the increase in band gap suppresses the bipolar effect of carriers at high temperatures.In addition,solid solution crystal defects and multiscale nanosecond phases greatly enhance phonon scattering,and extremely low lattice thermal conductivity(0.49 Wm^-1K^-1)is obtained at 823K in the Sn_0.95W_0.05Te sample.Ultimately,the average power of the Sn_0.97W_0.03Te sample in the 323K-823K interval is 17.79μWcm^-1K^-2and the average ZT value reaches 0.26,which is about 85.7%and 236%higher compared to the undoped SnTe alloy,respectively.（2）Based on the optimized phonon scattering project of Cu solid solution SnTe,the lattice thermal conductivity was further reduced by using rare earth element Y doping to optimize the electrical properties parameters.Meanwhile,Y doping introduced a large number of Y/Y₂Te₃multiscale nanocomposite second-phase structures,which combined with the originally existing large number of Cu defects in Cu alloying and Cu₂Te nanoprecipitated phases,thus building a multiscale phonon scattering center within the SnTe matrix,and the lattice thermal conductivity was further reduced to an ultra-low value of～0.42 Wm^-1K^-1at823 K.Finally,at 823 K,a ZT peak of 1.27 is obtained in the Sn_0.97Y_0.03Te-5%Cu₂Te sample.