The intra-crystalline cation partitioning over T- and M-sites in a synthetic Mg(Fe,Al)2O4 spinel sample has been determined as a function of temperature by Rietveld structure refinements from powder diffraction data, combining in situ high-temperature neutron powder diffraction (NPD; POLARIS diffractometer, at ISIS, Rutherford Appleton Laboratory, UK), to determine the Mg and Al occupancy factors, with in situ high-temperature X-ray powder diffraction, to fix the Fe3+ distribution. The results obtained agree with a two-stage reaction, in which an initial exchange between Fe3+ and Mg, the former leaving and the latter entering tetrahedral sites, is successively followed by a rearrangement involving also Al. The measured cation distribution has then been compared and discussed with that calculated by the Maximum Configuration Entropy principle, for which only NPD patterns have been used. The cation partitioning has finally been interpreted in the light of the configuration model of O'Neill and Navrotsky.
Bibliographical noteFunding Information:
Neutron scattering beam time at ISIS was provided by the CCLRC (now STFC). The research was financially supported by Italian MURST and CNR. The authors acknowledge Prof. Umberto Russo (University of Padova, Italy) for Mössbauer measurements. The authors are indebted to the reviewers for their suggestions that have really enhanced the original manuscript.
- Cation ordering versus temperature
- Neutron powder diffraction
- Synthetic spinel
- X-ray powder diffraction