The kinetics of the Pressure Induced Olivine-Spinel Phase Ransition Mg2GeO4
- Murli H. Manghnani and
- Yasuhiko Syono
Published Online: 21 MAR 2013
Copyright © 1987 by Terra Scientific Publishing Company (TERRAPUB), Tokyo.
High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto
How to Cite
Will, G. and Lauterjung, J. (1987) The kinetics of the Pressure Induced Olivine-Spinel Phase Ransition Mg2GeO4 , in High-Pressure Research in Mineral Physics: A Volume in Honor of Syun-iti Akimoto (eds M. H. Manghnani and Y. Syono), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM039p0177
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1987
Print ISBN: 9780875900667
Online ISBN: 9781118664124
- Mineralogy and Crystal Chemistry;
- Phase transformations;
- High Pressure-High Temperature Research
The kinetics of phase transitions in solids were studied with energy dispersive diffraction techniques. Complete diffraction spectra were measured in rapid sequence every 45 s. Also, by using the window method, the intensity variation of a narrow pre-selected energy window, containing one reflection, was passed along the channels in a multichannel analyzer over time. The multichannel analyzer was thus operated as a single-channel analyzer. The minimal recording time was 0.1–0.5 s.
Using the full X-ray diffraction pattern method, the kinetics of the phase transformation in Mg2GeO4, which is isostructural to the mantle-relevant mineral forsterite Mg2SiO4, was investigated in the experimental range 0–20 kbar and 800–1200°C. Phase transition was found to be accompanied by a density increase of 8.76%. Kinetic behavior of the olivine spinel phase transformation was investigated in seven transformation cycles with different P-T conditions. A total of 109 spectra were recorded and evaluated. The gradual growth of the spinel phase with time could be analyzed by fitting the data to the Avrami equation. Several full spectra (i.e., those recorded at every time step) were analyzed by profile fitting, thereby yielding integrated intensities. These intensity values were consequently used in structure factor and least-squares calculations to determine the crystal structure, particularly the cation occupancy. This procedure allowed a detailed analysis of the behavior of the cations Ge and Mg as they migrate into the oxygen frame. The transformation (i.e., the crystallization of the spinel phase) began with a rearrangement of the anion lattice from a distorted hcp arrangement to a cubic, close-packed arrangement. After a considerable delay of about 15 min, the octahedral and tetrahedral voids were filled; this could be observed experimentally through the measurement of reflections with contributions from Mg and Ge in the A- and B-sites.