EFFECT OF OXYGEN STOICHIOMETRY ON THE ELECTRICAL-PROPERTIES OF LA0.5SR0.5COO3 ELECTRODES

We report on the metal-insulator transition of La0.5Sr0.5CoO3 thin fil ms deposited by pulsed laser ablation on LaAlO3 substrates. The films were cooled in oxygen partial pressures between 760 and 10(-5) Ton and electrical resistivity of the films was measured as a function of coo ling oxygen pressure. La0.5Sr0.5CoO3 films changed from metallic to in sulating behavior depending on their oxygen content. A defect model ha s been proposed to explain this transition and the change in conductiv ity is related to the change in the oxidation state of the cobalt ions . The model explains the relationship between oxygen partial pressure and electrical conductivity in La0.5Sr0.5CoO3, which describes the exp erimental dependence reasonably well. Positron annihilation studies we re also done on the same set of samples and the S parameter was seen t o increase by 8% from a fully oxygenated sample to a sample cooled in 10(-5) Torr. (C) 1997 American Institute of Physics.