Pressure-Induced Sharp Coordination Change in Liquid Germanate

Abstract

Local structures around germanium in liquid germanate have been investigated by means of in situ x-ray absorption measurements up to 9 GPa at 1273 K. Liquid germanate consisting of tetrahedrally coordinated germanium contracts with increasing pressure without significant changes in the local structure up to 2.5 GPa and then shows an abrupt fourfold-to-sixfold coordination change around 3 GPa. The coordination change is completed below 4 GPa where upon a high-density liquid consisting of octahedrally coordinated germanium becomes stable. The $\mathrm{Ge}{\mathrm{O}}_{\mathrm{6}}$ octahedron in the high-density liquid is more compressible than that in solids.