Dore, P., Sacchetti, A., Postorino, P., Congeduti, A., Gorelli, F., and Ulivi, L.
Recent infrared absorption measurements performed at different pressures and temperatures on the La0.75Ca0.25MnO3 manganite provided an estimate of the insulator-to-metal transition temperature T IM( P), i.e., the P- T phase diagram of a pseudocubic manganite. Here we consider in detail the P- and T-dependence of the absorption spectral weights n *. The n *( T, P) behavior gives evidence of phase-separation between conducting and insulating domains in the P-T phase diagram, and allows to establish the occurrence of a characteristic temperature T * ≅ 0.6 T IM. For T > T *, when insulating domains decrease on decreasing temperature or on increasing pressure, it is possible to distinguish a metallic region (connected metallic domains) for T * < T < T IM, and an insulating region (disconnected metallic domains) for T > T IM. Below T *, no reduction of the insulating domains, that may still exist, occurs. [ABSTRACT FROM AUTHOR]