C M B Henderson et al 2007 J. Phys.: Condens. Matter 19 076214 doi:10.1088/0953-8984/19/7/076214
C M B Henderson1,2, J M Charnock1,2 and D A Plant2
Show affiliationsThe distribution of cations between tetrahedral (A) sites and octahedral (B) sites in ferrite spinels has been studied using K-edge x-ray absorption spectroscopy. The samples include natural and synthetic end-member magnetites (Fe3O4), a natural Mn- and Zn-rich magnetite (franklinite) and synthetic binary, ternary and quaternary ferrites of stoichiometry M2+M23+O4, where M2+ = Mg, Co, Ni, Zn and M3+ = Fe, Al. XAS data were obtained for all metals. Complete, unfiltered, EXAFS spectra were refined to determine the percentage distribution of each element over the A and B sites and these data were combined with microprobe analyses to quantify the tetrahedral occupancy for each element in each sample. Measured site occupancies and an internally consistent set of (M–O)A and (M–O)B bond lengths were used to calculate unit-cell parameters, which show excellent agreement with measured values, pointing to the reliability of the measured occupancy factors. The average occupancies determined for the tetrahedral sites in ferrites are (atoms per formula unit) Mg 0.44, Co 0.24, Ni 0.11, Zn 0.76, Al 0.11 and Fe3+ 0.92–0.19. The wide range found for Fe3+ is consistent with it playing a relatively passive role by making good any A-site deficit left by the other competing cations.
78.70.Dm X-ray absorption spectra
61.50.Lt Crystal binding; cohesive energy
61.50.Nw Crystal stoichiometry
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
Issue 7 (21 February 2007)
Received 18 December 2006, in final form 8 January 2007
Published 2 February 2007
C M B Henderson et al 2007 J. Phys.: Condens. Matter 19 076214
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