Evidence of Phase Separation in the P-T Phase Diagram of the La0.75Ca0.25MnO3 Manganite by Infrared Measurements

Recent infrared absorption measurements performed at different pressures and temperatures on the La 0.75 Ca 0.25 MnO 3 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 con- sider 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 tempera- ture 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 metal- lic 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.