Title

Crystal Chemistry of the Hydrothermally Synthesized Na₂(Mn1-xFex2+)₂Fe3+(PO₄)₃ Alluaudite-type Solid Solution

Abstract

Several compounds of the Na₂(Mn1-xFex2+)₂Fe3+(PO₄)₃ solid solution have been hydrothermally synthesized at 400 °C and 1 kbar; pure alluaudite-like compounds have been obtained for x = 0.00, 0.25, 0.50, 0.75, and 1.00. Rietveld reÞ nements of the powder X-ray diffraction patterns indicate the presence of Na+ at the A1 and A2' sites, Mn2+ and Fe2+ at the M1 site, and Mn2+, Fe2+, and Fe3+ at the M2 site. the presence of small amounts of Na+ at the M1 site and Mn2+ at the A1 site indicates a partially disordered distribution of these cations. an excellent linear correlation has been established between the M1-M2 distance and the energy of the infrared band attributed to the M2+-O vibrations. the Mössbauer spectra, measured between 85 and 295 K, were analyzed in terms of a model which includes the next-nearest neighbor interactions at the M2 and M1 crystallographic sites. Fe2+ and Fe3+ isomer shifts are typical of the alluaudite structure and exhibit the expected second-order Doppler shift. the derived iron vibrating masses and Mössbauer lattice temperatures are within the range of values expected for iron cations in an octahedral environment. the Fe2+ and Fe3+ quadrupole splittings are typical of the alluaudite structure, and the temperature dependence of the Fe2+ quadrupole splitting was Þ t with the Ingalls model, which yielded a ground state orbital splitting of ca. 460 to 735 cm 1 for the Fe2+ sites. the isomer shifts and quadrupole splittings of Fe2+ at the M1 site are larger than those of Fe2+ at M2, indicating that the M1 site is both larger and more distorted than the M2 site.

Department(s)

Chemistry

Sponsor(s)

National Science Foundation of Belgium
Ministere de la Region Wallonne

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2005 Mineralogical Society of America, All rights reserved.

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