Premium
Crystal structure solution for the A 6 B 2 O 17 ( A = Zr, Hf; B = Nb, Ta) superstructure
Author(s) -
McCormack Scott J.,
Kriven Waltraud M.
Publication year - 2019
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520619001963
Subject(s) - crystallography , crystal structure , superstructure , neutron diffraction , polyhedron , orthorhombic crystal system , valence (chemistry) , rietveld refinement , powder diffraction , x ray crystallography , pentagonal bipyramidal molecular geometry , formal charge , chemistry , materials science , diffraction , physics , geometry , mathematics , thermodynamics , organic chemistry , optics
Zr 6 Ta 2 O 17 , Hf 6 Nb 2 O 17 and Hf 6 Ta 2 O 17 crystal structure solutions have been solved using synchrotron X‐ray powder diffraction and neutron powder diffraction in conjunction with simulated annealing, charge flipping and Rietveld refinement. These structures have been shown to be isomorphous with the Zr 6 Nb 2 O 17 superstructure, leading to the classification of the A 6 B 2 O 17 ( A = Zr, Hf; B = Nb, Ta) orthorhombic compound family with symmetry Ima 2 (No. 46). The asymmetrical structural units of cation‐centred oxygen polyhedra used to build the structure are as follows: (i) one set of symmetry‐equivalent six‐coordinated polyhedra, (ii) three sets of symmetry‐equivalent seven‐coordinated polyhedra and (iii) one set of symmetry‐equivalent eight‐coordinated polyhedra. The potential for cation order and disorder was discussed in terms of cation atomic number contrast in X‐ray and neutron powder diffraction as well as the bond valence method. In addition, the structural mechanisms for experimentally observed compositional variations within the solid solution range can be attributed to the addition or removal of a set of symmetry‐equivalent seven‐coordinated polyhedra accompanied by corresponding oxygen tilts within the A 6 B 2 O 17 structure.