Metal-insulator Transition in a Pyrochlore-type Ruthenium oxide, Hg2Ru2O7(11)

A new pyrochlore ruthenium oxide, Hg2Ru2O7 was synthesized under a high pressure of 6 GPa. In contrast to the extensively studied Ru4+ oxides, this compound possesses a novel Ru5+ valence state, corresponding to a half-filled t_2g_3 electron configuration.

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Fig. 3 (Color online) (a) Temperature dependence of thermal conductivity and lattice parameter, a for Hg 2Ru 2O 7. The lattice parameter at both high and low temperatures was tentatively indexed with a cubic cell. The dotted line is a guide for the eyes. (b) X-ray powder diffraction patterns (Cu K α1 and α2) above (130 K) and below (90 K) the transition temperature for the selected indexes. Note that the peak shape changes are probably due to a

lowering of symmetry.