Centers of charge nonuniformity in absorption spectra of lanthanum manganites

In order to study the microscopic nature of the phase separation in lanthanum manganites, experimental investigations were made of the optical, electrical, and magnetic properties of La1- deltaMnO3 and La0.9Sr0.1MnO3 lanthanum manganite single crystals. The infrared absorption spectra revealed two bands at 0.14 eV and 0.35 eV whose intensity was sensitive to the magnetic order. The different temperature dependence of the electrical resistivity (semiconducting) and the transmission (metallic) below the Curie ferromagnetic temperature indicates that an insulator-metal transition takes place in various regions of the insulating matrix, i.e., phase separation occurs. Characteristic features of the properties and the nature of the phase separation in these compounds can be explained using a model of polar (hole [MnO68-](JT) and electron [MnO610-](JT)) pseudo-Jahn-Teller clusters which form centers of charge nonuniformity in the crystal. (C) 2000 MAIK "Nauka/ Interperiodica".