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Crystal structure of calcium vanadate-phosphate fluoride

Published online by Cambridge University Press:  18 March 2019

Z. L. Dong*
Affiliation:
Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
T. J. White
Affiliation:
Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
*
a)Author to whom correspondence should be addressed. Electronic mail: zldong@ntu.edu.sg

Abstract

Apatite-type materials AI4AII6(BO4)6X2 have two unique cations sites AI and AII, which can host large mono-, di- tri- and tetra-valent cations. The average cation radii will affect the twist angle and lattice constants. However, there are few reports on the influence of B site substitutions on the twist angle and lattice parameters. It is believed that the lattice constant variation as a function of B site substitutions may not follow the same twist-angle model as proposed for A site. This work reports our results on the crystal chemistry of synthetic apatite Ca10(VxP1−xO4)6F2 obtained through the crystal structure characterization using Rietveld refinement and high-resolution transmission electron microscopy. The quantification of vanadium/phosphorus partitioning in BO4 tetrahedra showed that equilibrium with more than 70% substitution of phosphorous by vanadium was difficult to achieve unless longer annealing (about 1 week at 900 °C) was employed. In comparison with the apatites with different ionic radii at AI and AII sites, Ca10(VxP1−xO4)6F2 apatites with different ionic radii at B site show little twist angle variation for the whole series, which indicates that the dilation of unit cell constants is mainly because of the expansions of BO4 tetrahedra when A site cation is fixed.

Type
Technical Articles
Copyright
Copyright © International Centre for Diffraction Data 2019 

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