Transport of carriers in perovskite oxides: Manganites, cobaltites, cuprates

The temperature-dependent de resistivity rho(T) has been investigated for P r0.65Ca0.35MnO3 and La0.5Sr0.5CoO3 films prepared by pulsed-laser depositio n. The formation of a metallic phase below the Neel temperature and evidenc e for a crossover from a charge-disordered to a charge-ordered state at 205 K were found for the Pr0.65Ca0.35MnO3 films. It was shown that the anomalo us behavior of rho(T) for the La0.5Sr0.5CoO3 films resulted from transition s between high- and low-spin states of the Co3+ ions. The microwave measure ments of high-T-c YBCO films showed that the unusual behavior of the surfac e resistance for compounds overdoped with oxygen also originated from the e xistence of and an ordering trend for the magnetic impurities. These result s manifest the important role of the phase-separation phenomenon in determi ning the transport properties of magnetoresistive manganites and cobaltites and of the superconducting cuprates.