Characterization of the metallic phases in BaCo0.9Ni0.1S1.87 - art. no. 140101

The temperature dependence of the resistivity along the c axis and in the a -b plane of layered BaCo0.9Ni0.1S1.87 has been measured on a single crystal under hydrostatic pressures. The monoclinic metallic (LTM) phase stable at T less than or equal to 150 K is suppressed under a pressure P>1.5 kbar; i t has a nearly isotropic conductivity. Pressure induces an insulator-metal (IM) transition at P>10 kbar within the tetragonal phase, A change from a n early isotropic conduction to a highly anisotropic conduction is associated with the IM transition. Isotropic conduction in the LTM phase is consisten t 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 metalli c phase are typical of those of a normal metal.