Molecular dynamics study of the crystal structure and phase relation of the GeO2 polymorphs

A two-body interatomic potential model for GeO2 polymorphs has been determined to simulate the structure change of them by semi-empirical procedure, total lattice energy minimization of GeO2 polymorphs. Based on this potential, two polymorphs of GeO2; alpha-quartz-type and rutile-type, have been reproduced using the molecular dynamics (MD) simulation techniques. Crystal structures, bulk moduli, volume thermal expansion coefficients and enthalpies of these polymorphs of Ge0(2) were simulated. In spite of the simple form of the potential, these simulated structural values, bulk moduli and thermal expansivities are in excellent agreement with the reliable experimental data in respect to both polymorphs. Using this potential, MD simulation was further used to study the structural changes of Ge02 under high pressure. We have investigated the pressure-induced amorphization. As reported in previous experimental studies, quartz-type GeO2 undergoes pressure-induced crystalline-to-amorphous transformation at room temperature, the same as other quartz compounds; SiO2, AlPO4. Under hydrostatic compression, in this study, alpha-quartz-type GeO2 transformed to a denser amorphous state at 7.4 GPa with change of the packing of oxygen ions and increase of germanium coordination. At higher pressure still, rutile-type GeO2 transformed to a new phase of CaCl2-type structure as a post-rutile candidate.