Bibliographic Citation
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| DOI | 10.1016/j.jssc.2008.04.046 |
| Title | The role of the coordination defect: A new structural description of four fluorite-related sesquioxide minerals, bixbyite (Mn{sub 2}O{sub 3}), braunite (Mn{sub 7}SiO{sub 12}), braunite II (CaMn{sub 14}SiO{sub 24}), parwelite (Mn{sub 10}Sb{sub 2}As{sub 2}Si{sub 2}O{sub 24}), and their structural relationships |
| Creator/Author | Bevan, D.J.M. [School of Chemistry, Physics and Earth Sciences, Flinders University of South Australia, Bedford Park, South Australia (Australia)], E-mail: Ray.Martin@sci.monash.edu.au ; Martin, R.L. [School of Chemistry, Monash University, Clayton, Victoria (Australia)] |
| Publication Date | 2008 Sep 15 |
| OSTI Identifier | OSTI ID: 21128439 |
| Other Number(s) | Journal ID: ISSN 0022-4596; JSSCBI; TRN: US08R3038010070 |
| Resource Type | Journal Article |
| Resource Relation | Journal Name: Journal of Solid State Chemistry; Journal Volume: 181; Journal Issue: 9; Other Information: DOI: 10.1016/j.jssc.2008.04.046; PII: S0022-4596(08)00223-5; Copyright (c) 2008 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA) |
| Subject | 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ANTIMONY IONS; ARSENIC COMPOUNDS; ARSENIC IONS; CALCIUM COMPOUNDS; FCC LATTICES; MANGANESE IONS; MANGANESE OXIDES; PHOSPHATES; SILICON COMPOUNDS; SILICON IONS; TUNGSTEN IONS; VACANCIES |
| Description/Abstract | The anion-deficient, fluorite-related structures of the manganese-based minerals bixbyite (Mn{sub 2}O{sub 3}), braunite (Mn{sub 7}SiO{sub 12}), braunite II (CaMn{sub 14}SiO{sub 24}) and parwelite (Mn{sub 10}Sb{sub 2}As{sub 2}Si{sub 2}O{sub 24}) are reinterpreted in terms of the coordination defect (CD) theory to gain new insights into their structural interrelationships. CDs are extended, octahedral defects centred by an anion vacancy and including its immediate atomic environment: it is represented as {open_square}M{sub 4}O{sub 6}, where the symbol {open_square} is the anion vacancy. The bixbyite motif is a CD dimer (two edge-sharing octahedra), and this motif repeats, by further edge-sharing, around the 2-fold screw axes of the cubic structure. These same dimers are present in each of the other structures, but the presence of Si{sup 4+} in braunite and braunite II, together with that of other foreign cations such as As{sup 5+} and Sb{sup 5+} in parwelite, leads to different juxtapositions of these motifs. Moreover, the structure of braunite, Mn{sup 2+}(Mn{sup 3+}){sub 6}SiO{sub 12}, reflects the clustering of 12 Mn{sup 3+}-centred octahedra (MnO{sub 6}) around a central SiO{sub 4} tetrahedron to generate a structure for the [(Mn{sup 3+}){sub 6}SiO{sub 12}]{sup 2-} anion which is almost identical to that of the well-known cuboctahedral structure of the PO{sub 4}-centred heteropolytungstate anion, [(W{sup 6+}){sub 12}PO{sub 40}]{sup 3-}. The structure of braunite II, [Ca(Mn{sup 3+}){sub 14}SiO{sub 24}], is simply an intergrowth of slabs of bixbyite- and braunite-type structures, linked by the CaO{sub 8} cubes of the latter. Our various analyses of the reported structure of parwelite in terms of the only possible vacancy assignment have led to some apparent anomalies. We report briefly on these, and have decided to seek confirmation of the reported structure as a consequence. Despite the increasing complexity of these structures, there are clear and defining relationships in the distribution of CDs. The assumption of a close relationship to the fluorite parent in all these structures is based on the observation that the cation sub-lattices are essentially face-centred cubic, with the anions in the tetrahedral sites, so there is little variation from this between one structure and another. The cation contents, however, are very different in the four structures discussed here - a single cation species in bixbyite, two in the braunites and four in parwelite. This factor, and the topology of the CD arrangements, are structure-determining and confirm the close relationships between these four minerals. - Graphical abstract: The anion-deficient, fluorite-related structures of the manganese-based minerals bixbyite (Mn{sub 2}O{sub 3}), braunite (Mn{sub 7}SiO{sub 12}), braunite II (CaMn{sub 14}SiO{sub 24}) and parwelite (Mn{sub 10}Sb{sub 2}As{sub 2}Si{sub 2}O{sub 24}), are reinterpreted in terms of the Coordination Defect (CD) theory to gain new insights into their structural interrelationships. CDs are extended, defects centred by an anion vacancy and including its immediate atomic environment of 4 tetrahedrally coordinated metals and 6 octahedrally coordinated O atoms: it is represented as {open_square}M{sub 4}O{sub 6}, where the symbol {open_square} is the anion vacancy. The arrangement of {open_square}M{sub 4} tetrahedra in bixbyite is shown in the [111] projection. |
| Country of Publication | United States |
| Language | English |
| Format | Medium: X; Size: page(s) 2250-2259 |
| Availability | Available from http://dx.doi.org/10.1016/j.jssc.2008.04.046;INIS |
| System Entry Date | 2009 Dec 17 |
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