Crystal dynamics by neutron time-of-flight Laue diffraction in olivine up to 1573K using single frame methods

Olivine single crystals from a pallasitic meteorite have been found to undergo a peculiar ordering process with increasing temperature consisting of a noticeable Fe segregation into site M1 up to around 900 degrees C, followed by a sudden ordering reversal with Fe progressively and strongly segregating into site M2 as the temperature is increased up to our experimental limit of 1300 degrees C. The speed of the reactions has baffled all previous quenching studies from temperatures above about 800 degrees C. The details of the ordering process at temperatures close to the transition temperature were determined in situ from single frames of data collected using the time-of-flight Laue method. The constrained refinements obtained from these data yield lower precision than full data sets but allow the ordering to be characterised rapidly and reliably. The power of this method in monitoring such phase transitions is discussed. The far reaching geological implications of our findings are considered.