High-pressure neutron and X-ray studies on the Mott transition of BaCoS2

X-ray Rietveld analyses for BaCoS2 under high pressure and magnetic excitat ion measurements for BaCo1-xNixS2 at ambient pressure and for BaCoS2 under high pressure have been carried out. Atomic distances in a CoS5 pyramid abr uptly change in the narrow region around the Mott metal-insulator transitio n with increasing external pressure (p). It suggests that the redistributio n of electron numbers among the relevant bands occurs together with the p-i nduced Mott transition. The characteristic energy of the spin fluctuation b ehaves rather differently in two kinds of metallic phases induced by varyin g I and p, indicating that the main driving forces of the Mott transitions are different. (C) 1999 Elsevier Science Ltd. All rights reserved.