Kinetic study of the GeO₂ transition under high pressures using synchrotron X-radiation

An in situ observation of the structure transition of GeO₂ has been made under 3.0 GPa at various temperatures with a diamond-anvil pressure cell. The time-resolved energy-dispersive (ED) diffraction experiment was undertaken using synchrotron X-radiation. A profile analysis of ED spectra observed every 15 min elucidates the transition process from the α-quartz form (P3₂21, Z = 3) to the rutile form (P4₂/mmm, Z = 2). The time-resolved measurement of their diffraction intensity ratio reveals the change of the mass fraction of the transformed product with time, which provides the transition rate. A transition curve showed three stages at low temperature; firstly a long inductance period after initiation of heat supply, secondly a rapid initiation of transition and finally a marked deceleration of growth. At high temperatures the inductance period of the transition was not observable. The transition is extremely sluggish. An apparent activation energy was calculated by the Avrami–Erofeev equation for the solid-solid transition and found to be 57.4 kJ mol⁻¹.