Oxygen Level Dependent Lattice Dynamics of Na0.73CoO2-delta

Abstract

The optical and acoustic phonon branches of Na0.73CoO2-delta have been determined using Raman scattering and inelastic neutron scatterings, and their correlation with phononic thermal conductivity k(ph) in terms of oxygen-vacancy concentration delta was investigated. The experimentally observed phonon stiffening of the Raman-active E-1g mode suggests that oxygen vacancies may help stabilize texturing of Na ions that gives rise to higher k(ph) with increasing delta. The generalized phonon density of states characterized using inelastic neutron scattering exhibits subtle stiffening of acoustic and optical phonons with delta, which appears to be responsible for the variations in k(ph)(T) profile in the temperature range 323-923 K.