Berlin 2008 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 14: Magnetic Half Metals and Oxides

MA 14.8: Vortrag

Dienstag, 26. Februar 2008, 12:15–12:30, EB 202

Ab initio cluster calculations of Co³⁺ spin states in RBaCo₂O_5.5 (R=Ho,Gd) — Luidmila Siurakshina^1,2, •Beate Paulus³, and Viktor Yushankha² — ¹Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, 01187 Dresden — ²Joint Institute for Nuclear Research, 141980 Dubna, Russia — ³Physikalische und Theoretische Chemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin

We investigated the different Cobalt spin-states of two members of oxygen-deficient perovskites RBaCo₂O_5.5(R=Ho, Gd). These materials are promising compounds for ionic conductors necessary for solid oxide fuel cells. The studies involve ab-initio calculations for clusters at the multi-reference configuration interaction level to describe all spin-states at equal footing. The emphasis is made on the peculiar behaviors of the trivalent ions Co³⁺(3d⁶) in an octahedral and a pyramidal oxygen coordinations, which is related to a structural first-order phase transition in both compounds. Relative energy positions of low spin (S=0), intermediate spin (S=1) and high spin (S=2) cluster electron configurations are calculated for the low- and high-temperature lattice structures of RBaCo₂O_5.5. The calculated results and experimental structural data are analyzed and comprised in a model that enables us to catch the most prominent features common to the phase transition in both compounds.