Strain effects on the electronic and thermoelectric properties of n(Pbte)-m(bi2 te3 ) system compounds

Abstract

Owing to their low lattice thermal conductivity, many compounds of the n(PbTe)-m(Bi2 Te3 ) homologous series have been reported in the literature with thermoelectric (TE) properties that still need improvement. For this purpose, in this work, we have implemented the band engineering approach by applying biaxial tensile and compressive strains using the density functional theory (DFT) on various compounds of this series, namely Bi2 Te3, PbBi2 Te4, PbBi4 Te7 and Pb2 Bi2 Te5 . All the fully relaxed Bi2 Te3, PbBi2 Te4, PbBi4 Te7 and Pb2 Bi2 Te5 compounds are narrow band-gap semiconductors. When applying strains, a semiconductor-to-metal transition occurs for all the compounds. Within the range of open-gap, the electrical conductivity decreases as the compressive strain increases. We also found that compressive strains cause larger Seebeck coefficients than tensile ones, with the maximum Seebeck coefficient being located at −2%, −6%, −3% and 0% strain for p-type Bi2 Te3, PbBi2 Te4, PbBi4 Te7 and Pb2 Bi2 Te5, respectively. The use of the quantum theory of atoms in molecules (QTAIM) as a complementary tool has shown that the van der Waals interactions located between the structure slabs evolve with strains as well as the topological properties of Bi2 Te3 and PbBi2 Te4 . This study shows that the TE performance of the n(PbTe)-m(Bi2 Te3 ) compounds is modified under strains.