Studies on metal-insulator transition of pyrochlore compound Y2-xBixRu2O7

Various physical properties of Y2-xBixRu2O7 have been studied. The critical temperature To of a spin-glass transition observed in the system decreases with x and goes to zero at x = x(c) in the region of the insulator-metal phase boundary. The low temperature specific heat coefficient gamma increases with decreasing x from 2.0, has a maximum at x(c) and decreases with further decreasing x. In Y2Ru2O7, there exists a significant specific heat anomaly at T-G. Because the anomaly does not depend on the applied magnetic field; it seems to be due to a structural phase transition, suggesting that the spin-glass transition is induced by this transition. By detailed studies on the relationship between the transport properties and the transition temperatures T-G of Y2-xMxRu2O7 (M=Bi, Lu and Ca) and Y2Ru2-xTixO7, an intimate correlation of the itinerant nature with the structural transition is pointed out.