Volume changes during melting and heating of silicon and germanium melts

The temperature dependence of the density of silicon and germanium in the neighborhood of the crystal-melt phase transition is investigated by an improved thermometric method. Changes in volume occurring during transition from the solid to the liquid state are estimated. It is shown that the density increases in the process of crystal-melt phase transition and, accordingly, the specific volume decreases in both silicon and germanium; an increase in pressure noticeably decreases the melting points of both investigated substances. A linear temperature dependence of density in the liquid phase is obtained. The strength characteristics of interatomic bonds are estimated such as the characteristic Debye temperatures and root-mean-square dynamic displacements of atoms from the equilibrium position in the short-range order structure of the melts of the investigated substances. It is shown that the melting process noticeably weakens the cohesive forces between particles and substantially changes the pattern of their oscillation spectrum.