Hawthorne, F. C., Cooper, M. A. (2013) The crystal structure of chalcoalumite: mechanisms of Jahn-Teller-driven distortion in [6]Cu2+-containing oxysalts. Mineralogical Magazine, 77 (7) 2901-2912 doi:10.1180/minmag.2013.077.7.02
| Reference Type | Journal (article/letter/editorial) | ||
|---|---|---|---|
| Title | The crystal structure of chalcoalumite: mechanisms of Jahn-Teller-driven distortion in [6]Cu2+-containing oxysalts | ||
| Journal | Mineralogical Magazine | ||
| Authors | Hawthorne, F. C. | Author | |
| Cooper, M. A. | Author | ||
| Year | 2013 (October) | Volume | 77 |
| Page(s) | 2901-2912 | Issue | 7 |
| Publisher | Mineralogical Society | ||
| DOI | doi:10.1180/minmag.2013.077.7.02Search in ResearchGate | ||
| Mindat Ref. ID | 244449 | Long-form Identifier | mindat:1:5:244449:3 |
| GUID | 79ea16c3-e3f4-425f-a7ce-8e73c05d8c2e | ||
| Full Reference | Hawthorne, F. C., Cooper, M. A. (2013) The crystal structure of chalcoalumite: mechanisms of Jahn-Teller-driven distortion in [6]Cu2+-containing oxysalts. Mineralogical Magazine, 77 (7) 2901-2912 doi:10.1180/minmag.2013.077.7.02 | ||
| Plain Text | Hawthorne, F. C., Cooper, M. A. (2013) The crystal structure of chalcoalumite: mechanisms of Jahn-Teller-driven distortion in [6]Cu2+-containing oxysalts. Mineralogical Magazine, 77 (7) 2901-2912 doi:10.1180/minmag.2013.077.7.02 | ||
| Abstract/Notes | AbstractThe crystal structure of chalcoalumite, ideally Cu2+Al4(SO4)(OH)12(H2O)3, monoclinic, P21/n, Z = 4:a 10.228(3), b 8.929(3), c 17.098(6) Å, β 95.800(11)°, V 1553.6(1.5) Å3, has been refined to R1 = 3.08% for 4,022 unique observed (4σ) reflections collected on a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator, multilayer optics and an APEX-II CCD detector. In the structure of chalcoalumite, there is one S site, tetrahedrally coordinated by four O anions, with <S–O> = 1.472 Å. There are four Al sites with site-scattering values in accord with occupancy by Al and <Al–O> distances of 1.898–1.919 Å. There is one Cu site occupied by Cu2+ and coordinated by six anions in the [4 + 2] arrangement typical for octahedrally coordinated Cu2+. The short <Cu–O> distance of 2.086 Å is in accord with the low degree of bond-length distortion of the Cu octahedron. There are 19 anion sites: 4 sites are occupied by O atoms that are bonded to the S cation, 12 sites are occupied by (OH) groups that bond to all octahedrally coordinated cations, and 3 sites are occupied by (H2O) groups that are held in the structure solely by hydrogen bonding. The structure of chalcoalumite consists of interrupted sheets of edge-sharing Al and Cu octahedra of the form [Cu2+Al4(OH)12]2+ that intercalate layers of (SO4) tetrahedra and (H2O) groups. Chalcoalumite is a member of the nickelalumite group.Cu2+ϕ6(ϕ = O2–, (OH)–, (H2O)0) octahedra show a wide range of bond-length distortion away from the holosymmetric arrangement, driven by spontaneous symmetry-breaking of the degenerate electronic ground-state in holosymmetric octahedral coordination. Here, we examine the structural mechanisms that allow large octahedron distortions of this type. There are two mechanisms: (1) coupling of (usually parallel) octahedron distortions to a vibrational phonon, inducing a (often ferroelastic) phase transition in M2+-Cu2+ solid-solutions; (2) cooperative orientational disorder, where bond topology (polyhedron linkage) allows large differences in bond lengths within polyhedra to accord with the valence-sum rule of bond-valence theory. | ||
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