Calcium-lead fluoro-vanadinite apatites. II. Equilibrium structures
White, Timothy John
Date of Issue2004
School of Materials Science and Engineering
The synthetic vanadinites (PbxCa10-x)(VO4)6(F1-2yOy&y)2, 0.57 < x < 9 and 0.10 < y < 0.47, adopt the P63/m apatite structure with 9.7835 (3)≤a≤10.0531 (1)Å and 7.0318 (2)≤c≤7.3033 (1)Å. The calcium endmember is monoclinic, space group P21/m, with a = 9.7370 (3), b = 9.7358 (4), c = 7.00572 (9)Å,γ = 120.002 (5)°. For mixed metal compounds (x≠0) the partitioning of calcium and lead over the AI(4f) and AII(6h) positions is nonstoichiometric, with lead preferentially favouring the larger AII site at a partitioning coefficient kPb(AI/AII) ≅ 0.33 for all x < 7. A miscibility gap exists for 2 < x < 3. Trends in crystallographic parameters can be correlated through consideration of the AIO6 metaprism twist angle (γ) that can be used to derive ideal cell parameters from triangular anion networks.
Acta crystallographica B
© 2004 International Union of Crystallography. This paper was published in Acta Crystallographica B and is made available as an electronic reprint (preprint) with permission of International Union of Crystallography. The paper can be found at the following DOI: http://dx.doi.org/10.1107/S0108768104001843. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.