Cation partitioning versus temperature in (Mg0.70Fe0.23)Al1.97O4 synthetic spinel by in situ neutron powder diffraction |
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| Authors: | A Pavese G Artioli U Russo A Hoser |
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| Institution: | (1) Dipartimento di Scienze della Terra, Università di Milano, I-20133 Milano, Italy, IT;(2) Dipartimento di Chimica, Università di Padova, I- 35131 Padova, Italy, IT;(3) BENSC, Berlin Neutron Scattering Center, Hahn Meitner Institut, D-43100 Berlin, Germany e-mail: pavese@p8000.terra.unimi.it, DE |
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| Abstract: | Neutron powder diffraction experiments in the temperature range 300–1770 K were performed at BENSC, Berlin, Germany, on synthetic
(Mg0.70Fe0.23) Al1.97O4. The cation partitioning over the crystallographic tetrahedral and octahedral sites was determined as a function of temperature
through joint Rietveld refinements and advanced minimization techniques. The thermal expansion coefficients of the lattice
parameter and inter-atomic bond lengths were also obtained from the full-profile structure refinements. The behaviour of the
polyhedral bond-lengths, especially the T−O distances, and of the cell constant upon heating, clearly indicate that the interdiffusion
of tetrahedral and octahedral Mg/Al cations starts at about 950 K. This result is straightforwardly supported by the direct
analysis of the neutron site scattering factors: Fe always retains tetrahedral coordination at all temperatures, and the cation
rearrangement is entirely due to Mg and Al diffusion.
Received: 18 November 1997 / Revised, accepted: 23 August 1998 |
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| Keywords: | Synthetic spinels Neutron powder diffraction Ordering versus T |
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