Phonons and crystal structures of the $\ensuremath{\beta}$-pyrochlore superconductors ${\text{KOs}}_{2}{\text{O}}_{6}$ and ${\text{RbOs}}_{2}{\text{O}}_{6}$ from micro-Raman spectroscopy

Phonons and crystal structures of the $β$ -pyrochlore superconductors ${KOs}_{2} O_{6}$ and ${RbOs}_{2} O_{6}$ from micro-Raman spectroscopy

J. Schoenes, A.-M. Racu, K. Doll, Z. Bukowski, and J. Karpinski

Phys. Rev. B 77, 134515 – Published 18 April 2008

Abstract

The phonons and the crystal structures of the $β$ -pyrochlore superconductors ${KOs}_{2} O_{6}$ and ${RbOs}_{2} O_{6}$ are studied on single crystals by using micro-Raman spectroscopy. The symmetry of the modes is determined by polarization dependent measurements for various scattering geometries. It is concluded that the crystal structures are centrosymmetric $(F d \bar{3} m)$ . The vibrational frequencies have been computed from first principles and are in good agreement with the experimental data. The Raman-active rattling mode of the alkali ion is identified at 75 and $60 {cm}^{- 1}$ for the K and Rb compounds, respectively.