Evidence of Phase Separation in the P-T Phase Diagram of the La{sub}0.75Ca{sub}0.25MnO{sub}3 Manganite by Infrared Measurements

摘要

Recent infrared absorption measurements performed at different pressures and temperatures on the La{sub}0.75Ca{sub}0.25MnO{sub}3 manganite provided an estimate of the insulator-to-metal transition temperature T{sub}(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{sup}*. The n{sup}*(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{sup}* ≌ 0.6 T{sub}(IM). For T > T{sup}*, when insulating domains decrease on decreasing temperature or on increasing pressure, it is possible to distinguish a metallic region (connected metallic domains) for T{sup}* < T < T{sub}(IM), and an insulating region (disconnected metallic domains) for T > T{sub}(IM). Below T{sup}*, no reduction of the insulating domains, that may still exist, occurs.