Anomalous density variations of the molten chalcogenide system GeAsSe

An experimental method of measuring densities of melts with high vapour pressures is described. This method is based upon the absorption of high-energy gamma rays. The method enables densities to be measured even in the case of melts solidifying (or bulk samples melting) inside a sealed system, as long as certain conditions are satisfied. The results of investigations of some melts of the chalcogenide system GeAsSe are presented.The melts so far investigated show an increase in density at high temperatures which is super-imposed on the thermal expansion. The reason for these irregularities is an increase of the average coordination number caused by a change of the bonding system. The bonding system with one-sided overlapping of (sp^x)-hybrid bonding functions changes at higher temperatures to a system in which pσ-bonding functions are extended on more than one side of the atoms. This change of the bonding system explains the transition of the electrical conductivity of rhese melts at high temperatures from a semiconductor-like to a metallic-like conductivity. Because a pσ-bonding system enables the atoms to have a relatively high mobility the viscosities of these melts are very low at high temperatures and are similar to those of molten metals.