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- Title
Incommensurate modulation and thermal expansion of Sr<sub>3</sub>B<sub>2 + x</sub>Si<sub>1 − x</sub>O<sub>8 − x/2</sub> solid solutions.
- Authors
Volkov, Sergey; Bubnova, Rimma; Bolotina, Nadezhda; Krzhizhanovskaya, Maria; Belousova, Olga; Filatov, Stanislav
- Abstract
Crystal structures of Sr3B2 + xSi1 − xO8 − x/2 solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr3B2SiO8-Sr2B2O5 section of the SrO-B2O3-SiO2 system are refined using single-crystal X-ray diffraction data. Incommensurate structure modulations are mainly associated with various orientations of corner-sharing (B,Si)-polyhedra. Preference is given to the (3 + 2)-dimensional symmetry group Pnma(0βγ)000(0γ)000 for a single crystal compared with an alternate model of a twin formed by monoclinic components, each of them corresponding to the (3 + 1)-dimensional symmetry group P21/ n(0βγ). Single-phase polycrystalline samples of solid solutions are investigated by high-temperature X-ray powder diffraction in air. Orientation preferences of the BO3 units lead to a strong anisotropy of thermal expansion. Negative expansion is observed along the a axis over the temperature range 303-753 K. Anisotropy decreases both on heating and decreasing of the boron content.
- Subjects
STRONTIUM compounds; THERMAL expansion; CRYSTAL structure
- Publication
Acta Crystallographica Section B: Structural Science, Crystal Engineering & Materials, 2015, Vol 71, Issue 5, p489
- ISSN
2052-5192
- Publication type
Article
- DOI
10.1107/S2052520615011713