Study On The Performance Of BiCuSeO And SnSe As Thermoelectric Materials Based On First Principles

In previous studies,BiCuSeO was expected to be used in thermoelectric energy materials of 573-923 K,and SnSe was expected to be used in semiconductor chips,infrared optoelectronic devices,and anode materials for lithium-ion batteries.But the theoretical research is still incomplete and currently the calculation method of its anisotropic thermoelectric figure of merit is not reasonable.In this paper,the first-principles calculation method based on density functional theory is used to study the electronic characteristics of chalcogenous layered materials BiCuSeO and SnSe,and further combined with Boltzmann transport theory,lattice dynamics theory,and linear phonon Boltzmann equation to predicts the anisotropic thermoelectric properties(including Seebeck coefficient,electrical conductivity,power factor,thermal conductivity,and dimensionless thermoelectric figure of merit)of P-type and N-type doping,and discusses their transport performance.The main research contents include:Based on the VASP software,the effects of LDA,GGA(PBE),and GGA(PBE+HSE06)functional methods on lattice optimization are compared and analyzed.The GGA(PBE+HSE06)functional methods,which is more in line with experimental values and more ideal in prediction results,is selected.Bolt ZTra P2 software was used to solve the Boltzmann transport equation,and the anisotropic thermoelectric transport parameters of P-type and N-type doped BiCuSeO and SnSe crystals were calculated,Including Seebeck coefficient,electrical conductivity and electronic thermal conductivity with relaxation time parameter?.The DP constant E₁,the elastic constant C_ii,and the effective mass m*were calculated using the deformation potential(DP)theory,and the relaxation time?was obtained by combining the Boltzmann transport equation.The self-consistent iterative method included in Sheng BTE software was used to calculate the phonon Boltzmann equation,and the intrinsic thermal conductivity of the layered materials BiCuSeO and SnSe were theoretically predicted.We calculated the phonon frequency distribution,Grüneisen parameter,constant volume heat capacity,and Debye temperature.The research results show that the thermoelectric properties of layered crystals BiCuSeO and SnSe have strong anisotropy.Among them,the maximum thermoelectric figure of merit ZT(2.69)is obtained along the a-axis at 700 K and a carrier concentration of5.31×10¹⁹cm^-3for N-type SnSe,while the P-type obtained a maximum value of 1.14 along the b-axis at 700 K and a carrier concentration of 7.5×10¹⁹cm^-3.The maximum thermoelectric figure of merit ZT(2.315)is obtained along the c-axis at 900 K with a carrier concentration of 5.2×10¹⁹cm^-3for N-type BiCuSeO,while the P-type obtained a maximum value of 1.23 along the c-axis at 900 K and a carrier concentration of 1.98×10²⁰cm^-3.This study theoretically provides an effective way to improve the thermoelectric performance of BiCuSeO and SnSe,that is,to use the anisotropy of transport characteristics and regulate the carrier concentration to improve the thermoelectric performance of layered materials,thereby promoting related experimental research.