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Incommensurate modulation and thermal expansion of Sr 3 B 2 + x Si 1 − x O 8 − x /2 solid solutions
Author(s) -
Volkov Sergey,
Bubnova Rimma,
Bolotidezhda,
Krzhizhanovskaya Maria,
Belousova Olga,
Filatov Stanislav
Publication year - 2015
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520615011713
Subject(s) - monoclinic crystal system , anisotropy , crystallography , crystallite , thermal expansion , materials science , diffraction , bar (unit) , atmospheric temperature range , crystal structure , single crystal , x ray crystallography , crystal (programming language) , chemistry , physics , optics , thermodynamics , programming language , computer science , metallurgy , meteorology
Crystal structures of Sr 3 B 2 + x Si 1 − x O 8 − x /2 solid solutions with nominal compositions x = 0.28, 0.53, 0.78 in the Sr 3 B 2 SiO 8 –Sr 2 B 2 O 5 section of the SrO–B 2 O 3 –SiO 2 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 P 2 1 / n (0βγ). Single‐phase polycrystalline samples of solid solutions are investigated by high‐temperature X‐ray powder diffraction in air. Orientation preferences of the BO 3 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.