Pressure and temperature dependence of the Fano resonance in the Raman spectrum of A₂FeMoO₆ systems (A=Sr,Ca)

Abstract

We report on Raman measurements carried out on Ca₂FeMoO₆ and Sr₂FeMoO₆ double perovskites as functions of pressure (0-15 GPa) and of temperature (298-370 K). The Raman spectrum of both the samples is characterized by a phonon peak at ~460 cm⁻¹ whose large asymmetric profile is ascribed to a Fano resonance. The careful data analysis provides in particular the Fano asymmetry parameter q which results to be nearly independent from pressure and temperature, thus suggesting a remarkable stability of both charge-carrier density and charge-lattice coupling. Finally, our data allow us to ascribe the conductivity transition previously observed around 2 GPa in Sr₂FeMoO₆ not to an intrinsic property but to the pressure-induced opening of intergrain percolation paths.