Characterization of the metallic phases in BaCo0.9Ni0.1S1.87

Abstract

The temperature dependence of the resistivity along the c axis and in the a-b plane of layered ${\mathrm{BaCo}}_{0.9}{\mathrm{Ni}}_{0.1}{\mathrm{S}}_{1.87}$ has been measured on a single crystal under hydrostatic pressures. The monoclinic metallic (LTM) phase stable at $Tl~150\mathrm{K}$ is suppressed under a pressure $Pg1.5\mathrm{kbar};$ it has a nearly isotropic conductivity. Pressure induces an insulator-metal (IM) transition at $Pg10\mathrm{kbar}$ within the tetragonal phase. A change from a nearly isotropic conduction to a highly anisotropic conduction is associated with the IM transition. Isotropic conduction in the LTM phase is consistent with its crystallographic structure; the IM transition in the tetragonal phase has been interpreted to be due to a high-spin to low-spin transition of Co(II) ions. The resistivity and thermal conductivity of the LTM metallic phase are typical of those of a normal metal.