Optical phonons in R2BaMO5 oxides with M=Co, Ni, Cu, and R=a rare earth.

Abstract

Compounds with the formula ${\mathit{R}}_{2}$BaM${\mathrm{O}}_{5}$ where R=rare earth and M=Co, Ni, or Cu, have been studied with Raman spectroscopy. The lattice dynamics of the three different crystallographic phases adopted by these systems (space groups Immm, Pnma, and P4/mbm) is discussed in relation to the transition-metal--oxygen coordination, and to the binding M-O and R-O distances. An almost complete identification of the normal modes has been performed for the compounds with the P4/mbm structure and an estimation of the parameters of the M-O and R-O stretching force constants has been obtained for the Immm and P4/mbm structures.