Electrical resistivity of pyrochlore compounds R2Mo2O7(R =Nd, Sm, Gd, Tb, Y)

The electrical resistivity ofR2Mo2O7(R =Nd, Sm, Gd, Tb, Y) pyrochlores was measured in the temperature range 4.2 to 300 K. Metallic behavior is observed for Nd2Mo2O7, Sm2Mo2O7, and Gd2Mo2O7 which have relatively high magnetic ordering temperatures due to ferromagnetism on the molybdenum sublattice. A clear drop in resistivity is observed near the magnetic ordering point for all metallic materials. A resistance minimum observed at low temperatures, which may be due to the magnetic ordering of the rare-earth sublattice, is not completely understood. Tb2Mo2O7 and Y2Mo2O7, which show no molybdenum sublattice ordering down to 4.2 K, are semiconductors. However, the temperature dependence of the resistivity is not exponential. This unusual resistivity behavior is typical of degenerate semiconductors.