Pressure Induced Insulator-Metal Transition in Hexagonal BaTiO_<3-δ> (Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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The dc electrical resistivity ρ in the reduced hexagonal BaTiO_<2.98> single crystal was measured under hydrostatic pressures up to 3.1 GPa in the temperature range of 5 K to 300 K. The ρ along the hexagonal c axis is somewhat larger than that of the perpendicular direction. The ρ vs T curve changes the behavior at the temperature T_O, where the hexagonal to orthorhombic phase transition takes place : it behaves as a semiconductor and a metal at temperatures below and above T_O, respectively. With increasing pressure T_O decreases, and the metallic behavior dominates whole of the temperature range at pressures above P_C = 1.9 GPa. In the pressure-induced metallic phase, T^2-dependence of resistivity appears at low temperatures. This rule suggests that electrons in the Ti 3d band of BaTiO_3, are the same as electrons in a strongly correlated electron system. A band model is proposed to explain such insulator-metal transitions in SrTiO_3, cubic BaTiO_3, and hexagonal BaTiO_3.
社団法人日本物理学会の論文
2004-05-15