Metal-Nonmetal Transition in Liquids

Abstract

A brief review is presented on the aspects and mechanism of the metal­ nonmetal transition in the disordered systems. The electronic and thermo­ dynamic properties are discussed for expanded Hg and dilute amalgams near the liquid-gas critical point. In expanded liquid Hg a metal-nonmetal (M-NM) transition occurs at density near 9g/cm' and anomalous behaviors are found in the thermodynamic properties such as equation-of-state and isothermal compressibility. At low densities substantial volume contraction and large increase in conductivity are brought about by the addition of a small amount of the elements with high valency such as Bi and Pb to expanded liquid Hg. The semiconductor-metal transition is discussed for liquid and amorphous Se-Te mixtures. In the liquid mixture, the transition from Se-like loosely packed to Te-like densely packed structure occurs by changing the temperature, pressure and Te content. The transition may be associated with the change in the short-range order around Te atoms. In amorphous Seo.aTeo.s mixture a reproducible sharp semiconductor-metal transition is found under pressure. The semiconductor-metal transition near the liquid-liquid critical point is also described for liquid Tl-Se mixtures in the Se-rich region. The liquid-liquid two-phase region is diminished by the application of pressure. It is suggested that the metal-nonmetal transitions observed in the liquid and amorphous systems are closely related to the structural changes.