Layered Cobaltites: Synthesis, Oxygen Nonstoichiometry, Transport and Magnetic Properties

K. Condera, A. Podlesnyaka, E. Pomjakushinab and M. Stingaciua aPaul Scherrer Institut (PSI), WLGA, Villigen PSI 5232, Switzerland bHahn-Meitner-Institut (HMI), Glienicker Str. 100, Berlin 14109, Germany

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Received: 04 09 2006;

Complex cobalt oxide perovskite-derived compounds with a general formula LnBaCo2O5+x (Ln = rare earth) attracted considerable interests because of their interesting properties: magnetic and metal-insulator transitions, giant magnetoresistance, ionic conductivity, and a structural similarity to high temperature superconductors. All the compounds are oxygen non-stoichiometric (0<x<1) and the cobalt cations can adopt different oxidation and spin states. Compounds with x≈0.5 display a metal-insulator transition. We found that this transition is affected by an oxygen isotope substitution and is accompanied by structural changes and melting of the orbital ordering. Studies of the metal-insulator transition qualitatively support the models assuming rather carriers delocalization than a spin-state transition in Co3+.

DOI: 10.12693/APhysPolA.111.7 PACS numbers: 72.80.Ga, 71.27.+a, 75.47.De, 61.12.Ld, 71.70.Ej