Structural transition and metallization in liquid selenium

The insulator-metal transitions of different kinds caused by heating above the melting temperature under pressure of tens kilobars and by compressing at the critical temperature to a pressure of about 1.1 kbar occur in liquid selenium. At tens kilobars, metallization is interpreted as the forbidden energy band vanishing due to a gradual structural transition (melting of polymer chains) described by the Clapeyron-Clausius equation. At supercritical temperatures, the insulator-metal transition is caused by percolation of overlapping electron shells (classically accessible spheres) of virtual atoms in molecules Se₂ remaining when polymer chains decay. The percolation threshold in such a system has been found to increase due to coupling of virtual atoms. The thermally activated conductivity in the vicinity of percolation threshold has been calculated and compared with existing experimental data.