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Structure and physical property relations of Mn ilvaite; Part II, Electrical conductivity and thermopower

Fehr, Karl Thomas, J. Schneider, R. Hochleitner, and E. Schmidbauer (2005), Structure and physical property relations of Mn ilvaite; Part II, Electrical conductivity and thermopower, Physics and Chemistry of Minerals, 32(5-6), 388-399, doi:10.1007/s00269-005-0012-7.

Abstract
Structural and compositional data as well as Fe-57 Mossbauer parameters were determined on a natural Mn-rich monoclinic ilvaite crystal ( ideal composition CaFe22+ Fe3+ Si2O8(OH)) which was used for electrical conductivity and thermopower measurements ( part 2 of this paper). A zonar structure was found by electron microprobe analysis with a strong decrease in Mn concentration from the rim to the centre of the crystal in a plane perpendicular to the [ 001] direction. X-ray powder diffraction analysis of the most Mn-rich composition was performed. Mn2+ cations populate preferentially M2 sites of the ilvaite unit cell ( space group P21/a), to a lower extent they reside on M1 and a reduced part is on Ca sites. The monoclinic angle was determined to beta = 90.178(4) degrees. The structural results are compared to literature data for other natural Mn-rich as well as low-impurity ilvaites; this concerns in particular the lattice b parameter and the undecided issue of the varying b angle. In the literature, the order parameter sigma, which describes the varying degree of ordering of Fe2+ Fe3+ pairs on M11 and M12 sites in chains running parallel to the [ 001] direction, and structural defects are thought to be related to beta. The interrelationship between beta and sigma with respect to a possible twin domain structure is discussed. Various Fe-57 Mossbauer spectra were recorded between 151 K and 327 K. Mossbauer parameters and Fe2+/ Fe3+ concentration ratios were determined from the fits to the spectra. Fitting of subspectra was accomplished with the idea to find assignments of Fe2+ and Fe3+ doublets in agreement with X-ray results. The fraction of Mn2+ substituting Fe2+ on M1 sites could be estimated.
BibTeX
@article{id440,
  author = {Karl Thomas Fehr and J. Schneider and R. Hochleitner and E. Schmidbauer},
  journal = {Physics and Chemistry of Minerals},
  number = {5-6},
  pages = {388-399},
  title = {{Structure and physical property relations of Mn ilvaite; Part II, Electrical conductivity and thermopower}},
  volume = {32},
  year = {2005},
  doi = {10.1007/s00269-005-0012-7},
}
EndNote
%0 Journal Article
%A Fehr, Karl Thomas
%A Schneider, J.
%A Hochleitner, R.
%A Schmidbauer, E.
%D 2005
%N 5-6
%V 32
%J Physics and Chemistry of Minerals
%P 388-399
%T Structure and physical property relations of Mn ilvaite; Part II, Electrical conductivity and thermopower
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Printed 18. Aug 2019 06:59