Strongly-Correlated Electron Behavior and Metal-Insulator Crossover in Ru-Based Oxides with Pyrochlore-Type Structure

The pyrochlore ruthenates Pb 2 − x RE x Ru 2 O 7 − δ ( RE = Y, Nd, Eu, Sm, Lu) have been successfully synthesized by the solid-state reaction. The solid-solution compounds of Pb 2 − x RE x Ru 2 O 7 − δ show a crossover from metallic to insulating with increasing x . Owing to a localized magnetic moment on Ru site, these compounds with x > 0 . 2 also indicate the spin-glass like behaviors at low temperature ( T < T SG ). As a result of electric resistivity measurements, the crossover was observed around x = 0 . 4 which is closely related to the spin-glass like behavior. In the metallic region, values of electric resistivity obey T 2 dependencies which indicate the strong correlation between electrons in these compounds. It is concluded that the crossover from metallic to insulating is based on the strongly-correlated electron system.

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