Author: Simon Redfern

Abstract
The development of high-P/T methods for the study of phase transitions in minerals by neutron diffraction will be discussed. These methods have been employed on a number of systems, using the ISIS neutron spallation source at Rutherford Appleton Laboratory, U.K. The ability of neutrons to measure intracrystalline cation distributions from site scattering is found to be particularly valuable, in particular in those phases which contain elements with huge scattering contrasts, such as the Fe-Ti oxides. Examples of cation order-disorder studied in situ at high P and T thus far include Mg-Al order-disorder in spinels, Fe-Ti order-disorder in titanohematites, and Mn-Mg order in tephroite-olivines. Results demonstrate that the enthalpies of order-disorder in these systems frequently show significant pressure dependences which modify the high-T disorder characteristics of order-disorder transformations