Calcium-lead fluoro-vanadinite apatites. I. Disequilibrium structures
Date of Issue
2004School
School of Materials Science and Engineering
Version
Published version
Abstract
The synthetic vanadinites (PbxCa10-x)(VO4)6F2δ, 1 < x < 9,
adopt a P63/m apatite structure with 9.7590 (1) ≤ a ≤ 10.1179 (1) Å and 7.0434 (3) ≤ c ≤ 7.4021 (1) Å. The
partitioning of calcium and lead over the AI(4f) and AII(6h) positions is nonstoichiometric with lead preferentially
entering the larger AII site. High-resolution electron microscopy
showed that samples annealed for 10 h at 1073 K are in
disequilibrium with calcium- and lead-rich microdomains coexisting
at unit-cell scales. For (Pb5Ca5)(VO4)6F2δ, sintering in
excess of 2 weeks is required for the metals to order
macroscopically. As annealing progresses, c/a, the partitioning
coefficient kPb(AI/AII) and the AIO6 metaprism twist angle (φ)
adjust ooperatively to enlarge the apatite channel, and
thereby accommodate higher lead content. These results
demonstrate that φ is a sensitive measure of disequilibrium
and a useful device for monitoring changes in apatite topology
as a function of composition.
Subject
DRNTU::Engineering::Materials::Ecomaterials
Type
Journal Article
Series/Journal Title
Acta crystallographica B
Rights
© 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/S0108768104001831. 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.
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http://dx.doi.org/10.1107/S0108768104001831
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