The role of the coordination defect (CD) in the structures of anion-deficient, fluorite-related compounds.
The various superstructure phases that occur with the anion-deficient compositions of binary oxides MO(2-x) with the fluorite structure as parent are explored here in terms of the original 'coordination defect' (or CD) concept in which each vacant oxygen site, □, is 'coordinated' by six O atoms thereby creating the octahedral 'structure-determining' entity [M(3.5)□O(6)]. It emerges that the structure and composition of each anion-deficient (polymorph) phase can be described in terms of crystallographic `motifs' which comprise sets of parallel coplanar polygons based on ½<210>(F) and ½<111>(F) CD linkages.
1/1 Wellington Tce, Fullarton, South Australia 5063, Australia. judge.bevan@optusnet.com.au
D J M
DJ
Bevan
Lisandra L
LL
Martin
Raymond L
RL
Martin
binary oxides; coordination defect concept; superstructure phases