Critical phenomena and metal-nonmetal transition in the miscibility gap region of liquid Tl1−xSex (x < 1/3) alloys

Abstract

The very first electroconductivity σ(T) and thermopower S(T) measurements of separated phases of liquid T11−xSex (x < 1/3) alloys under high pressure of argon gas are carried out. In the transition region the electronic properties of the melts investigated vary greatly. The metal-nonmetal transition temperatures which are determined separately from σ(T) and S(T) data for the melt of the same concentration, coincide within experimental error limits. The liquid-liquid coexistence curve on the phase diagram of the T1-Se system from the T1-rich side is determined on the basis of σ(T) measurements. It was then determined that 1. the coordinates of the critical point are xc = 19.7 ± 0.1 at% Se and Tc = 1036 ± 2.1 K, 2. the coexistence curve diameter deviates from the “rectilinear law” in the vicinity of the critical point, and moreover, its singular part is described by the index 1 - α = 0.87 ± 0.02, 3. the coexistence curve in the x-T plane in the vicinity of the critical point may be described by the same expression with two different β index values depending on reduced temperature, i.e. β1 = 0.35 ± 0.02 at 10−3 < ϵ ≦ 8 × 10−3 and β2 = 0.49 ± 0.02 at ϵ > 8 × 10−3. Our experiments demonstrate a close correlation of the metal-nonmetal electron transition with phase separation. In particular, the influence of conductivity electrons on the formation of the critical region is discussed.