The Germanium-Oxygen System

High-temperature x-ray diffraction patterns of germanium plus germanium oxide GeO2 between 750° and 1400°C, showed that germanium monoxide GeO is not a stable compound. At elevated temperatures germanium can dissolve up to 60 atom percent of oxygen. The oxygen causes first a slight expansion and then a contraction of the Ge lattice. At 850° and 930°C, the x-ray pattern of a germanium-oxygen compound, consisting of equimolecular quantities of germanium and oxygen, showed only the germanium pattern. At 1000° and higher (above the melting point of pure germanium, 965°C), the germanium pattern disappears, and liquid-like structure is visible, though the sample is still solid (melting point 1430°C). When the temperature is lowered again to 930°C, the germanium pattern reappears. The electrical resistivity of the Ge and GeO2 mixture shows a sharp break at 970°C. In the germanium-oxygen compound we thus have a disordering of the germanium lattice above the melting point of pure germanium.