Centers of charge nonuniformity in absorption spectra of lanthanum manganites

In order to study the microscopic nature of the phase separation in lanthan um manganites, experimental investigations were made of the optical, electr ical, and magnetic properties of La1- deltaMnO3 and La0.9Sr0.1MnO3 lanthanu m manganite single crystals. The infrared absorption spectra revealed two b ands at 0.14 eV and 0.35 eV whose intensity was sensitive to the magnetic o rder. The different temperature dependence of the electrical resistivity (s emiconducting) and the transmission (metallic) below the Curie ferromagneti c temperature indicates that an insulator-metal transition takes place in v arious regions of the insulating matrix, i.e., phase separation occurs. Cha racteristic features of the properties and the nature of the phase separati on in these compounds can be explained using a model of polar (hole [MnO68- ](JT) and electron [MnO610-](JT)) pseudo-Jahn-Teller clusters which form ce nters of charge nonuniformity in the crystal. (C) 2000 MAIK "Nauka/ Interpe riodica".