Electronic structure and thermoelectric properties of p-type Ag-doped Mg2Sn and Mg2Sn1-xSix (x = 0.05, 0.1)

An experimental and theoretical study of p-type Ag-doped Mg2Sn and Mg2Sn1-xSix (x = 0.05, 0.1) is presented. Band structure calculations show that behavior of Ag in Mg2Sn depends on the site it occupies. Based on Bloch spectral functions and density of states calculations, we show that if Ag substitutes for Sn, it is likely to form a resonant level; if it substitutes for Mg, a rigid-band-like behavior is observed. In both cases, the doped system should exhibit p-type conductivity. Experimentally, thermoelectric, thermomagnetic, and galvanomagnetic properties are investigated of p-type Mg2Sn1−xSix (x = 0, 0.05, 0.1) samples synthesized by a co-melting method in sealed crucibles. Ag effectively dopes the samples p-type, and thermoelectric power factors in excess of 20 μW cm−1K−2 are observed in optimally doped samples. From the measured Seebeck coefficient, Nernst coefficient, and mobility, we find that the combination of acoustic phonon scattering, optical phonon scattering and defect scattering results in an energy-independent scattering rate. No resonant-like increase in thermopower is observed, which correlates well with electronic structure calculations assuming the location of Ag on Mg site.