Probing the metal-insulator transition in Ni(III)-oxide perovskites

Systematic measurements of the resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ and thermoelectric power $\alpha \mathrm{}\left(T\right)\mathrm{}$ under hydrostatic pressure have been made on single-valent perovskites of the family ${\mathrm{LnNiO}}_3$ $\left({\mathrm{L}\mathrm{n}=\mathrm{L}\mathrm{a},\mathrm{}\mathrm{P}\mathrm{r},\mathrm{}\mathrm{N}\mathrm{d},\mathrm{}\mathrm{Sm}}_{0.5}{\mathrm{Nd}}_{0.5}\right);$ they distinguish the influences of chemical and hydrostatic pressure on the insulator-metal transition occurring at a temperature $T_t.$ The data suggest the coexistence above $T_t$ of fluctuations of more localized electrons in a Fermi-liquid background with an ordering of the two phases into a static charge-density/spin-density wave below $T_t.$