First Principles Calculation Study Of HfCoX (X=As, Sb, Bi) And YRhSn (Y=V, Nb, Ta) Half-Heusler Thermoelectric Material

In recent years,the research on thermoelectric materials has deepened gradually.Researchers find that the conversion efficiency of semiconductor thermoelectric materials is much higher than that of metallic thermoelectric materials.With the development of computational materials science,various new thermoelectric materials are constantly being discovered,filling the gaps in the field of thermoelectricity.Based on the density functional theory,combined with deformation potential theory,semi-classical Boltzmann transport theory and Slack model,the electronic structure,mechanical properties and thermoelectric performances of18-electron half-Heusler compounds Hf Co X（X=As,Sb,Bi）and YRh Sn（Y=V,Nb,Ta）have been studied and discussed in this paper.When calculating the energy band structure,we found that Boltz Tra P2 software adopted the rigid band approximation method,which could effectively solve the Boltzmann transport equation without establishing the structure of p-type and n-type compounds,respectively,greatly reducing the intensity of calculation.The specific research process and conclusions are as follows:I use density functional theory to calculate the energy band structure and density of states of Hf Co X（X=As,Sb,Bi）compounds.The results show that Hf Co As and Hf Co Sb compounds are indirect bandgap semiconductors,while the Hf Co Bi compound is a direct bandgap semiconductor.Near the Fermi level,the slopes of the density of states of n-type and p-type Hf Co X（X=As,Sb,Bi）compounds are very large,which means that they have very high Seebeck coefficients.The Hf Co X（X=As,Sb,Bi）compounds meet the Born-Huang stability criterion,and there is no imaginary frequency in the phonon dispersion,which conforms to mechanical stability and dynamic stability.Due to its high relaxation time,Seebeck coefficient,and conductivity,the Hf Co As compound ultimately achieved a high ZT value of 1.74.Then discussing the electronic structure and thermoelectric properties of YRh Sn（Y=V,Nb,Ta）compounds.As far as I know,there is no report on the electronic and thermoelectric properties of Nb Rh Sn and VRh Sn compounds.We found that all three compounds are ionic materials with ductile properties and anisotropic mechanical properties.In phonon dispersion of the Ta Rh Sn compound,the high-frequency acoustic mode and low-frequency optical mode intersect,indicating that the compound has strong phonon-phonon scattering.The power factors of n-type YRh Sn（Y=V,Nb,Ta）compounds have a local trough,which may be caused by the correlation between the electrical conductivity and Seebeck coefficient.The final calculation results show that for n-type Ta Rh Sn and Nb Rh Sn compounds,they reach ZT values of 2.13 and 1.41 at carrier concentrations of 1.22×10²⁰ cm^-3 and 1.26×10²⁰ cm^-3,respectively.The research results of this paper have been compared with other relevant studies and have achieved good agreement.It is hoped that these results can provide valuable directions for related experiments.