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 alpha-quartz form (P3(2)21, Z = 3) to the rutile form (P4(2)/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 the 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.