Calcium-lead fluoro-vanadinite apatites. II. Equilibrium structures

• Main Authors: Dong, Zhili, White, Timothy John
• Other Authors: School of Materials Science & Engineering
• Format: Article
• Language: English
• Published: 2011
• Subjects: DRNTU::Engineering::Materials::Ecomaterials
• Online Access: https://hdl.handle.net/10356/90583; http://hdl.handle.net/10220/6921
• Institution: Nanyang Technological University

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.