Alkali metal dynamics in the β-pyrochlores A0s206 (A = K, Rb, Cs) and their prospects as thermoelectric materials

Abstract

The β-pyrochlores A0s206 (A = K, Rb, Cs)are extensively studied because of their superconducting properties that are believed to be linked to the rattling modes of the alkali metals. The rattling of small atoms encaged in large cavities has been mown to be important for the thermoelectric performance of both clathrates and skutterudites, and fuels our interest in the osmates. The vibrational dynamics of the K atom in KOs206, differs significantly from those of Rb and Cs in their respective pyrochlores and a complex low-energy signature was recently observed using inelastic neutron scattering (INS). To gain insight into the dynamics of the alkai metais in this system, we studied these materials using ab initio molecular dynamics (MD) simulations validated against experimental INS spectra. Combining the results of MD simulations with phonon dispersion curves, calculated from ab initio lattice dynamics (LD) enabled the prediction of thermoelectric properties for these materials using the Boltzmann transport equation. This talk will discuss the alkali metal dynamics in terms of their relevance in the potential development of this class of materials for thermoelectric applications.