Pressure and temperature dependence of the Fano resonance in the Raman spectrum of A(2)FeMoO(6) systems (A=Sr,Ca)

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 similar to 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.