The structural properties of synthetic Sr-gehlenite, Sr2Al2SiO7
Abstract
The crystal structure of Sr-gehlenite Sr2Al2SiO7 is tetragonal with space group P[unk]21m, a = 7.820(1), c = 5.264(1) Å, Z = 2 and Dx = 3.821 g · cm−1, and was refined to R = 3.6% using 345 non-equivalent reflections. This compound is confirmed to be isotypic with gehlenite Ca2Al2SiO7. In this Sr-gehlenite there is the same partial ordering with Al in T(1) tetrahedra and Al1/2Si1/2 in T(2) ones as in natural gehlenite. This Al/Si distribution is in good agreement with those predicted through the universal bond-strength method and the one corrected for oxygen coordination. Cross-hatched and lamellar structures observed in the latter, however, were neither recognized in the former nor in synthetic gehlenite with the same Al/Si ordering, and so it is not conceivable that these lamellar structures are due to only Al/Si ordering.
Judging from the crystallographic geometry of melilite isomorphs, the chemical expansion of their lattice parameters is interpreted as mainly due to the effect of rotation of the T(1) tetrahedra and enlargement of the T(2) – O(1) – T(2′) angles.
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Articles in the same Issue
- Pyrite-type silicon diphosphide p-SiP2: Structural parameters and valence electron density distribution
- Indexing of electron double diffraction patterns from partially-decomposed cadmium halide crystals
- The refinement of unit cell parameters from two-circle diffractometer measurements
- The crystal structure of acenaphte (9,10b) quinolizinium-13-ethoxycarbonyl bromide sesquihydrate [(C22H16NO2)+Br−.1.5H2O]
- One-phase seminvariants of first rank
- Estimation of the electrooptic Kerr effect in ADP and DKDP crystals*
- Korrektur des Absorptionsfaktors für eine ebene, undurchlässige Pulverplatte und zum symmetrischen Braggfall analogen Strahlengang
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