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Physics and Chemistry of Minerals

, Volume 45, Issue 3, pp 249–257 | Cite as

Deficiency of water molecules in the crystallographic structure of vauxite

  • A. Van Alboom
  • G. M. da Costa
  • E. De Grave
Original Paper
  • 95 Downloads

Abstract

A vauxite mineral sample from Huanuni, Bolivia, was studied by XRD, TGA and Mössbauer spectroscopy. The XRD revealed the sample as having the typical triclinic structure of vauxite. The chemical formula was determined as (Fe0.88Mn0.01)Al1.99(PO4)2(OH)1.75(H2O)5.31, implying some Fe2+, OH and H2O deficiencies. The TGA curve showed ca. 27% loss of weight over a temperature range from 80 to 400 °C, supposedly due to the loss of water and hydroxyl groups. For the first time, Mössbauer spectra for vauxite were collected over a wide temperature range between 9 and 310 K. No magnetic ordering was detected. The spectra could be successfully and consistently analyzed by a superposition of four doublet subspectra. On the basis of the relation between the center shift and the mean Fe-ligand distance on the one hand and the center shift values for the various doublets on the other hand, one doublet was assigned to Fe(2). For the other doublets, it is proposed that, as a result of the H2O deficiency in the structure of the present vauxite sample, vacancies are present in the second coordination spheres of some Fe(1) and that these vacancies affect the quadrupole splitting of the corresponding Fe(1) cations, thus causing three Fe(1) doublet components in the Mössbauer spectra. The temperature variations of center shift and quadrupole splitting of the various doublet contributions are presented and discussed.

Keywords

Vauxite Mössbauer spectroscopy Center shift Quadrupole splitting Crystal field calculation 

Notes

Acknowledgements

This work was funded by the Fund for Scientific Research—Flanders, Belgium.

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Copyright information

© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

  1. 1.Department of Applied PhysicsUniversity of GhentGhentBelgium
  2. 2.Chemistry DepartmentFederal University of Ouro PretoOuro PretoBrazil
  3. 3.Department of Physics and AstronomyUniversity of GhentGhentBelgium

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