Insulator-metal transitions: Recent experimental results

Experimental results relating to insulator-metal transition problems in V2O3, VO2, Ti4O7, and NiS are reviewed. The controversial nature of the high temperature Mott transition in V2O3 is commented upon. The pairing interaction in VO2 and Ti4O7 is shown to be one of the important features in such transitions. The itinerant nature of conduction electrons in NiS in the ground state is shown to have been established.