Optical-active phonons in A3Fe2B″O9 (A=Ca, Sr; B″ =Te, W) double perovskites

Abstract

Raman scattering and infrared transmittance techniques are used to investigate the phonons of the Sr3Fe2TeO 9(SFTO), Sr3Fe2WO9(SFWO), and Ca3Fe2WO9(CFWO) double perovskites at 300 K. While SFTO and SFWO crystallize in a tetragonal structure belonging to the I4/m space with two formulas per unit cell (Z=2), CFWO crystallizes in a monoclinic structure belonging to the space group P 21/n with Z=2. The observed spectra are very similar to that of the prototype cubic (Fm̄3m) double perovskite, indicating that both the tetragonal and monoclinic structures result from small distortions of the cubic cell. The assignment of the optical phonons follows that given for the prototype Fm̄3m double perovskites. © 2010 American Institute of Physics.