Infrared study of charge delocalization induced by pressure in the La0.75Ca0.25MnO3 manganite -: art. no. 184410

We measured the pressure dependence of the room-temperature infrared absorption spectrum of the pseudocubic La0.75Ca0.25MnO3 manganite. On increasing pressure up to 10 Gpa we observe the increase of a broad band associated with polaronic absorption, which partially screens the high-frequency phonon at high pressures. We also measured absorption spectra of the same sample as a function of temperature, and of the layered Sr1.5La0.5MnO4 manganite as a function of pressure. The comparison between different sets of spectra clearly shows that the increase of the broad-band absorption observed in the La0.75Ca0.25MnO3 manganite is due to a pressure-induced charge delocalization process. However, the metallic state is not achieved at room temperature, at least in the explored pressure range.