Framework distortion by large ions in MAlSi2O6 aluminosilicates with keatite structure
Baumgartner, Bruno; Müller, Gerd
European Journal of Mineralogy Volume 2 Number 2 (1990), p. 155 - 162
published: Apr 17, 1990
manuscript accepted: Nov 9, 1989
manuscript received: Jun 23, 1989
ArtNo. ESP147050202001, Price: 29.00 €
Abstract NaAlSi2O6 and KAlSi2O6 with a keatite-type structure have been synthesized from LiAlSi2O6 (“β-spodumene”) via HAlSi2O6 by ion exchange. Lattice constants vary systematically from a = 7.541(1), c = 9.156(2) in LiAlSi2O6 over a = 7.483(2), c = 9.629(2) in NaAlSi2O6 to a = 7.429(2), c = 9.984(2) in KAlSi206. The crystal structures have been determined from X-ray powder diffraction data by the Rietveld method for NaAlSi2O6 and KAlSi2O6. Framework topology and space group symmetry (P43212) are unaffected by ion exchange. Space requirements of the large cations cause considerable and systematic distortions of the T-O-T bond angles, however.