The insulating and metallic states of metal-insulator transition (MIT) compounds with the K2NiF4-type structure have been studied through resistivity, heat capacity and magnetic susceptibility measurements. In the insulating state of the 3d transition-metal oxide Pr2-xSrxNiO4, resistivity measurements reveal a real-space ordering of doped holes, similar to La2-xSrxNiO4, but with weaker doping dependence and different charge-ordering temperatures. Additional hole doping results in a break-up of the polaron ordered state and metallic behavior for x≈1.0. In the 4d and 5d transition-metal oxide Sr2Ir1-xRuxO4, heat capacity (γ0 ≈ 30 mJ/mol K2) and magnetic susceptibility (x0 ≈ 1 × 10-3 emu/mol) reveal electronic correlations. The Wilson ratio (X0/γ0) decreases as the MIT (x ≈ 0.7) is approached from the metallic side, suggesting, however, that the MIT is not driven by electron correlations. The importance of the structural distortion and localized to itinerant magnetic transition accompanying the MIT is addressed.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering