The structure of natural fresnoite, Ba2TiSi2O8, from the sanbornite deposits of eastern Fresno County, California, has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P4bm(alpha;alpha; 1/2)(-alpha; alpha; 1/2)0gg, cell parameters a = 8.5353 (6), c = 10.4128 (7) A ° , modulation vectors q1=0.3020(3)(a*+b*) q2= 0.3020(3) (-a*+b*). Data collection was performed on an Xcalibur CCD diffractometer at 110 K. The structure was refined from 3452 reflections to final R = 0.0123. The model includes modulation of both atomic positions and displacement parameters. As a consequence of the Ba and O positional modulation, eight-, nineand tenfold Ba coordinations occur throughout the structure. The change of coordination around the Ba atom is clearly represented by the deformation of the pentagonal rings, as seen from a projection along [001]. The deformed pentagonal rings correspond to Ba atoms with eight- and nine fold coordinations and form octagonal clusters closely resembling those observed in the incommensurate structure of melilitetype compounds.
Superspace-symmetry determination and multidimensional refinement of the incommensurately modulated structure of a natural fresnoite / L.BINDI; M. DUSEK; V. PETRICEK; P. BONAZZI. - In: ACTA CRYSTALLOGRAPHICA. SECTION B, STRUCTURAL SCIENCE. - ISSN 0108-7681. - STAMPA. - B62:(2006), pp. 1031-1037. [10.1107/S0108768106030059]
Superspace-symmetry determination and multidimensional refinement of the incommensurately modulated structure of a natural fresnoite.
BINDI, LUCA;BONAZZI, PAOLA
2006
Abstract
The structure of natural fresnoite, Ba2TiSi2O8, from the sanbornite deposits of eastern Fresno County, California, has been solved and refined as an incommensurate structure in five-dimensional superspace. The structure is tetragonal, superspace group P4bm(alpha;alpha; 1/2)(-alpha; alpha; 1/2)0gg, cell parameters a = 8.5353 (6), c = 10.4128 (7) A ° , modulation vectors q1=0.3020(3)(a*+b*) q2= 0.3020(3) (-a*+b*). Data collection was performed on an Xcalibur CCD diffractometer at 110 K. The structure was refined from 3452 reflections to final R = 0.0123. The model includes modulation of both atomic positions and displacement parameters. As a consequence of the Ba and O positional modulation, eight-, nineand tenfold Ba coordinations occur throughout the structure. The change of coordination around the Ba atom is clearly represented by the deformation of the pentagonal rings, as seen from a projection along [001]. The deformed pentagonal rings correspond to Ba atoms with eight- and nine fold coordinations and form octagonal clusters closely resembling those observed in the incommensurate structure of melilitetype compounds.File | Dimensione | Formato | |
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