Transport Properties of Cubic Crystalline Ge$_{2}$Sb$_{2}$Te$_{5}$: A Potential Low-temperature Thermoelectric Material

Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) has been widely used as a popular phase change material. In this study, we show that it exhibits high Seebeck coefficients 200 - 300 $mu$V/K in its cubic crystalline phase ($it{c}$-GST) at remarkably high $it{p}$-type doping levels of $sim$ 1$times$10$^{19}$ - 6$times$10$^{19}$ cm$^{-3}$ at room temperature. More importantly, at low temperature (T = 200 K), the Seebeck coefficient was found to exceed 200 $mu$V/K for a doping range 1$times$10$^{19}$ - 3.5$times$10$^{19}$ cm$^{-3}$. Given that the lattice thermal conductivity in this phase has already been measured to be extremely low ($sim$ 0.7 W/m-K at 300 K),citep{r51} our results suggest the possibility of using $it{c}$-GST as a low-temperature thermoelectric material.

Possible Superconductivity in Fe-Sb Based Materials: Density Functional Study of LiFeSb

We investigate the electronic and other properties of the hypothetical compound LiFeSb in relation to superconducting LiFeAs and FeSe using density functional calculations. The results show that LiFeSb in the LiFeAs structure would be dynamically stable in the sense of having no unstable phonon modes, and would have very similar electronic and magnetic properties to the layered Fe based superconductors. Importantly, a very similar structure for the Fermi surface and a spin density wave related to but stronger than that in the corresponding As compound is found. These results are indicative of possible superconductivity analogous to the Fe-As based compounds if the spin density wave can be suppressed by doping or other means. Prospects for synthesizing this material in pure form or in solid solution with FeTe are discussed.

Ab Initio Phonon Dispersions for PbTe

We report first principles calculations of the phonon dispersions of PbTe both for its observed structure and under compression. At the experimental lattice parameter we find a near instability of the optic branch at the zone center, in accord with experimental observations.This hardens quickly towards the zone boundary. There is also a very strong volume dependence of this mode, which is rapidly driven away from an instability by compression. These results are discussed inrelation to the thermal conductivity of the material.