Pressure and temperature dependence of the Fano resonance in the Raman spectrum of A2 FeMo O6 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 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 chargecarrier 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. D