Studies on Metal-Insulator Transition of Pyrochlore Compound Y2-xBixRu2O7

Abstract

Various physical properties of Y _{2- x} Bi _x Ru ₂ O ₇ have been studied. The critical temperature T _G 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 γ increases with decreasing x from 2.0, has a maximum at x _c and decreases with further decreasing x . In Y ₂ Ru ₂ O ₇ , 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 Y _{2- x} M _x Ru ₂ O ₇ (M=Bi, Lu and Ca) and Y ₂ Ru _{2- x} Ti _x O ₇ , an intimate correlation of the itinerant nature with the structural transition is pointed out.