Volume changes during melting and heating of silicon and germanium melts

The temperature dependence of the density of silicon and germanium in the n eighborhood of the crystal-melt phase transition is investigated by an impr oved thermometric method. Changes in volume occurring during transition fro m 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 su bstances. 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 ord er structure of the melts of the investigated substances. It is shown that the melting process noticeably weakens the cohesive forces between particle s and substantially changes the pattern of their oscillation spectrum.