Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Andrut, M. Articles by Najorka, J. Search for Related Content GeoRef GeoRef Citation

Characterization of ammonioleucite (NH₄)[AlSi₂O₆] and ND₄ -ammonioleucite (ND₄)[AlSi₂O₆] using IR spectroscopy and Rietveld refinement of XRD spectra

¹ Institute for Mineralogy and Crystallography, University of Vienna - Geozentrum, A-1090 Vienna, Austria
² GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany
³ Corus Research, Development & Technology, Ceramics Research Centre, PO Box 10000, 1970 Ijmuiden, The Netherlands

^* E-mail: dharlov{at}gfz.potsdam.

Ammonioleucite, (NH₄)[AlSi₂O₆], and its deuterated analogue ND₄-ammonioleucite (ND₄)[AlSi₂O₆] have been synthesized in 20–150 mg amounts at 300°C and 500 MPa in 5 mm wide, 4 cm long Au capsules using Rene’ metal hydrothermal autoclaves. The resultant product consists of 20–30 µm-size single tetragonal crystals as well as 50–100 µm wide clumps of ingrown crystals. Infrared (IR) spectra obtained from powdered samples are assigned on the basis of T_d symmetry for both the ammonium and deutero-ammonium ion. They show triply degenerate vibrational bands (i.e. ₃ and ₄), some overtones, and combination modes from NH⁺₄ and ND⁺₄ While T_d symmetry for NH⁺₄ in ammonioleucite is not strictly correct due to distortion of the NH⁺₄ molecule, the non-cubic field is not large enough at room temperature to cause a substantial splitting in the bands. However, this perturbation is documented in the IR spectra by a substantial increase in the FWHH as well as the occurrence of shoulders on the broadened bands. In contrast, at lower temperatures, the observed band splittings in the former triply degenerated states of ₃ and ₄ could be explained by an effective local field with D₂ symmetry.

Rietveld refinement indicates that ammonioleucite, like leucite, has a tetragonal structure with space group symmetry I4₁/a. Here the NH⁺₄ molecule replaces the K⁺ cation on the 8-fold co-ordinated W site, which has m symmetry. Substitution of NH⁺₄ for K⁺ in the leucite structure results in an increase of the cell parameter a, whereas c is slightly reduced. The mean <W–O> bond length of ammonioleucite is increased in comparison to leucite from 3.00 to 3.12 Å whereas the mean <T–O> bond length of 1.65 Å remains unchanged. This results in an increase in the volume of the polyhedron hosting the NH⁺₄ molecule as well as a decrease in distortion for structural channels parallel to the <111> direction, formed by the arrangement of the six-fold rings, on which the W cations are located. The same effect is also observed, in general, when Rb⁺ or Cs⁺ is substituted for K⁺ in leucite.

KEYWORDS: ammonioleucite, IR spectroscopy, Rietveld refinement, XRD