Reverse metal–non-metal transition in semiconducting melts

Electrical conductivity, σ(T), and thermopower, α(T), measurements were performed for liquid TlAsSe2, CuTlSe2, Cu0.2(CuAsSe2)0.8, Cu0.4(CuAsSe2)0.6, and Cu0.6(CuAsSe2)0.4 alloys in a wide temperature range (700<T<1800 K) under ambient pressures of argon gas (up to 25 MPa). A reverse metal–non-metal high temperature transition is observed when temperature increases to about 1500 K. A mechanism involving the opening of a pseudogap is proposed. The mechanism suggests formation of both a mobility edge responsible for the electrical conductivity behavior, and a density of states edge that is responsible for the thermopower behavior.