Phonon spectra of superionic sodium and potassium oxides

Abstract

The alkali-metal oxides in the cubic antifluorite structure exhibits fast ion conduction, with potential applications such as solid state batteries, gas detectors, and fuel cells. Despite its possible usefulness, sodium and potassium oxides remain largely untouched experimentally, perhaps due to difficulties in preparation and preservation of these crystals. Very little is known about the behaviour of phonons in these oxides, and the investigations of phonons have in the past played a crucial role in the understanding of superionicity in these materials. Motivated to determine and understand the role of phonons in these oxides, we have undertaken the theoretical investigation on the phonon properties of Na2O and K2O by applying lattice dynamical simulation method. In this work we are investigating the zone centre phonons and phonon spectra of these compounds by applying a short range force constant model and considering the interatomic interactions up to third nearest neighbour.