"l'etragonal Germanium Dioxide and Equilibria in the Ge-O-H System

The thermodynamic stability of tetragonal germanium dioxide has been characterized by measurements of the equil ibrium Hf/H20 ratios in the tem-perature range 830~176 Results are extrapolated to 298 ~ using estimated heat capacities, to give the standard thermal parameters, and to the tetra-gonal-hexagonal transition point to give the free energy of formation of both modifications at that temperature. Hence, using published entropy and specific heat data for hexagonal germanium dioxide, the standard thermal parameters of this modification are computed. Sizeable crystals of tetragonal GeO2 have been grown by vapor transport under near-equi l ibr ium conditions. The aims of this paper are to establish the energy relationships of the solid modifications of germanium dioxide. There are two crystall ine allotropes, hex-agonal and tetragonal, and there is also a glassy form, all of which persist at room temperature and atmos