METAL-INSULATOR-TRANSITION IN THIOSPINEL CUIR2S4

We have discovered the existence of metal-insulator transition at appr oximately 220 K in the new thiospinel CuIr2S4. The electrical conducti vity, sigma, for sintered-powder specimens drops abruptly from 2 x 10( 2) S.cm-1 to 5 x 10(-1)S.cm-1 at T(M-I) approximately 220 K with decre asing temperature. At temperatures T<T(M-I), CuIr2S4 exhibits a semico nductive behavior with thermally activated conductivity, which is fitt ed by the formula: sigma = Aexp(-q/k(B)T). The slope of the lnsigma vs l/T curve just below the transition gives an activation energy of q = 4.7 x 10(-2) eV for the conduction.