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

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.

Metal-insulator Transition in a Pyrochlore-type

Ruthenium oxide, Hg2Ru2O7

Ayako Yamamoto1, 2, *, Peter A. Sharma1, Yoshihiko Okamoto1, 2, Aiko Nakao1, Hiroko Aruga Katori1, 2, Seiji Niitaka1, 2, Daisuke Hashizume1, and Hidenori Takagi1, 2, 3

1 RIKEN (The Institute of Physical and Chemical Research), Hirosawa Wako, 351-0198

2CREST, Japan Science and Technology (JST),

3 Dept. Advanced Materials, Univ. Tokyo, Kashiwa-no-ha, Kashiwa 277-8561

(Received Feb. 1, 2007, accepted Feb. 9, 2007)

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 t2g3 electron configuration.

Hg2Ru2O7 exhibits a first order metal-insulator transition at 107 K,

accompanied by a structural transition from a cubic to lower

symmetry. The behavior of the magnetic susceptibility suggests the

possible formation of a spin singlet in the insulating low

temperature state.

KEYWORDS: metal-insulator transition, pyrochlore-type structure,

ruthenium oxide, geometrical frustration

* Corresponding author e-mail: ayako-yamamoto@postman.riken.jp

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