Metal-insulator Transition in a Pyrochlore-type Ruthenium oxide, Hg2Ru2O7(9)

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. 1 (Color online) X-ray photoemission spectra of Ru3d for Hg 2Ru 2O 7 and RuO 2 at room

temperature.