Thermal Conductivity Anomalies of RECoO_3 (RE=La-Nd) Related to Valency and Spin State of Co Ion(Condensed matter: structure and mechanical and thermal properties)

概要

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The thermal conductivities κ(T) of Co- and La-site-substituted LaCoO_3 were measured and the origin of the κ(T) peak was investigated. The sharp κ(T) peak at approximately 30K is strongly suppressed by the introduction of a small amount of Jahn-Teller (JT)-active Co^<4+> ions because of Co-site substitution by divalent ions such as Ni^<2+> and Cu^<2+>, similarly to the La-site substitution by Sr^<2+>. In contrast, the κ(T) peak of samples with the Co-site substituted by tetravalent ions such as Sn^<4+> and Zr^<4+>, which introduce Co^<2+> ions, moderately decreased. The temperature at which a small and broad κ(T) peak in the Pr-containing RECoO_3 [rare-earth (RE)=La_<1-y>Pr_y and Pr_<1-z>Nd_z] is also observable shifts from 110K for RE=La_<0.5>Pr_<0.5> to 180K for RE=Pr and Pr_<0.5>Nd_<0.5>, which corresponds to the spin-state transition temperature of Co^<3+> ions.
社団法人日本物理学会の論文
2008-08-15