Raman and infrared studies of the metal-insulator transition in BaCo1-xNixS2

The electronic states near the insulator-metal transition of stoichiometric BaCo1-xNixS2 were investigated utilizing the different selection rule for Raman scattering from reflection spectroscopy. The electronic Raman component at low energies is large even in the insulating phase at x = 0. The spectral intensity is preserved from 300 to 20 K in the insulating phase (x less than or equal to 0.18), whereas in the metallic phase (x greater than or equal to 0.24), the B-1g and B-2g spectra increase, as temperature decreases. It suggests that the change is induced by the itinerant electronic states through the mass-enhanced type insulator-metal transition. (C) 2000 Elsevier Science B.V. All rights reserved.