Effect of elemental substitutions on ruthenates with pyrochlore-type structure

Synthesis and physical properties of Pb2-xLnxRu2O7-δ (Ln, Y, Eu, Lu) phase are reported. The pyrochlore ruthenates Pb2-xLnxRu2O7-δ (Ln = Y, Eu, Lu) have been successfully synthesized by the solid-state reaction. The solid-solution compounds of Pb2-xLnxRu2O7-δ undergo a crossover from metallic (x = 0) to insulating (x = 2) with increasing x. Owing to a localized magnetic moment on Ru site, these compounds with x > 0.2 also indicate the spin-glass (SG) like behaviors at low temperature (T < TSG). From electric resistivity measurements for the Y-substituted system, the sample of x = 0.0 shows metallic behaviors and that of x = 1.0 shows insulating properties. In Pb2-xLnxRu2O7-δ system, the solid-solution compounds show from metallic (x = 0) behaviors to insulating (x = 2) behaviors with increasing x. In a similar manner as Pb2-xLnxRu2O7-δ system, it was found that TSG decreases monotonously with decreasing x and goes to zero at x 0.6. As a result of electric resistivity measurements, the samples with 0.4 ≤ x ≤ 0.8 show the metal-insulator (MI) transition at 10-30 K where the slope of temperature dependence of electrical resistivity (ρ) changes. In the metallic region, values of ρ obey T2-dependencies which indicate the strongly correlated electron behaviors in this system.