Physical properties and phase transitions of β Cu2-xSe (0.20≤x≤0.25)

beta-Cu2-xSe (0.20 less than or equal to x less than or equal to 0.25) showed a transition to a two-phase mixture of (alpha+beta) at similar to 250 K, and then the beta phase transformed to an ordered new phase at 180 K. The 180 K transition is characterized by the jump of electrical resistivity rho, Hall coefficient R-H, Seebeck coefficient S and magnetic susceptibility chi on tooling. Measurements of R-H and S revealed that the phase below 180 K is a degenerate p-type semiconductor, where the holes originate from the deficient copper atoms. The phase above the 180 K transition showed the two-hand conduction of majority holes and minority electrons. Magnetic susceptibility measurements showed that the compound is a diamagnet above similar to 180 K, and a paramagnet below similar to 180 K. (C) 1998 Elsevier Science S.A. All rights reserved.