Liquid metals and semiconductors under pressure

Abstract

Studies on the electronic and thermodynamic properties of liquid metals and semiconductors at high temperatures and high pressures are reviewed. A substantial decrease of volume for liquid alkali metals is brought about by the application of pressure. The interference function of liquid alkali metals with high pressure can be described by the hard-sphere model with a fixed packing fraction when one proceeds along the melting curve. For liquid Cs, the s–d resonance scattering plays an important role in the electron-transport properties at high pressures. In expanded liquid Hg, a metal–nonmetal transition occurs at a density near 9 g∙cm−3, and anomalous behaviour is found in the thermodynamic properties such as equation-of-state and density fluctuations. At low densities, substantial volume contraction and a large increase in conductivity are brought about by the addition of a small amount of Bi. At high temperatures and high pressures, liquid Se is transformed from a semiconducting state to a metallic state, accompanied by modification of chain structure. The measurements of sound velocity and optical properties reveal that the temperature and pressure at which the semiconductor–metal transition occurs are lowered by the addition of Te. It is suggested that the semiconductor–metal transition observed in liquid Se is induced by increasing fluctuations in the interchain distance and increasing interchain coupling. The electronic properties of liquid Se are substantially changed by the addition of impurity elements such as alkalis and halogens. Modification of chain structure is associated with the charge transfer between Se chains and impurity elements. To understand how the interchain coupling affects the electronic properties of liquid Se, the properties of the isolated Se chains confined in the pores of mordenite are studied. The pressure effects on the two-phase separation of liquid binary mixtures, such as metal–metal, metal–semiconductor, and metal – ionic salt mixtures, are also discussed.