1, Texas State University, San Marcos, Texas, United States
3, Universidade Federal de Vicosa, Rio Paranaiba, MG, Brazil
Group IV Tellurides are formidable functional materials, and lead tellurides are no exceptions. This simple rocksalt-type compound is widely known thermoelectric (TE) materials with excellent performances, among other applications. Recently , we have shown that the high values for the dielectric constant, together with anharmonic LA-TO coupling, reduces the lattice thermal conductivity and enhances the electronic conductivity in PbTe, which is good for TE devices. Moreover, it was also shown that by alloying this material with Se, the electronic conductivity of the alloys is also enhanced . But, it is not clear if the same occurs when alloying PbTe with Sn. We show, in this work, our theoretical results for the stability, vibrational and dielectric properties of Pb1-xSnxTe alloys. The calculations were carried out by using the Density Functional Theory, gradient conjugated techniques, and the plane-wave pseudopotential method (VASP and abinit codes). The alloys were described by both the Virtual Crystal and the Generalized Quasi-Chemical Approximations. Our results show that, while their lattice parameters obey Vegard’s rule, their bulk moduli, phonon frequencies and dielectric constant do not. Based on this feature, we have detected that when increasing the Sn concentration x, the anharmonic LA-TO coupling enhances and reaches its maximum for x ~ 0.70. This corresponds to the maximum value for the dielectric constant as well, and this alloy formation is stable from 600 to 800 K. Consequently, the obtained lattice contribution to the static dielectric constant is higher, when compared with both PbTe and SnTe bulk values, showing that the alloy can behave better as TE device than their bulk counterparts. We acknowledge support from FAPEMIG (grant CEX APQ 02695-14).
1. H. W. Leite Alves, et al., Phys. Rev. B 87, 115204 (2013).
2. Y. Pei, et al., Nature 473, 66 (2011).