Observation of Metal-Insulator Transition in Hollandite Vanadate, K_2V_8O_<16>(Cross-disciplinary physics and related areas of science and technology)

概要

論文の詳細を見る
We have synthesized hollandite vanadate, K_2V_8O_<16>, by a solid-state reaction under 4GPa at 1473K for one hour, and investigated its structural and electromagnetic properties. We found a metal-insulator transition with a two-step jump of resistivity of about three orders at around 170K. The magnetic susceptibility is reduced to a small value at the transition, suggesting the formation of V^<4+>-V^<4+> singlet pairs and V^<3+>-V^<3+> pairs in the low-temperature insulator phase. The transition is of first order accompanied by a structural change from a tetragonal to a monoclinic structure. The low-temperature phase has a superlattice of √<2>a×√<2>a×2c, where a and c denote the parameters of the primitive cell for the simple tetragonal hollandite structure, suggesting a charge ordering of V^<4+> and V^<3+>. We construct a possible charge order model from the obtained results, in which two kinds of double-chain formed by V^<3+> and V^<4+> chains and by single V^<4+> chains order in a manner that gives a superlattice of √<2>a×√<2>a in the a-b plane. The V^<4+>-V^<4+> and V^<3+>-V^<3+> pairs are formed in each chain along the c-axis, resulting in a duplication of the c-axis.
社団法人日本物理学会の論文
2006-07-15