The crystal structure of barite, β-BaSO4, at high temperatures

Abstract

Abstract The crystal structure of barite: β-BaSO4 (orthorhombic, Pnma, Z = 4, Dx = 4.48 g/cm3 at 25°C, μ = 120 cm−1 at 25°C, β → α transition temperature 1090°C) has been studied with single crystal X-ray diffraction methods at temperatures up to 1035°C. The a-axis keeps expanding at elevated temperatures, while the expansion of the b-axis nearly ceases, and that of the c-axis ceases from 1010°C. The scatter of the interatomic Ba—O and Ba—S distances tends to decrease at temperatures above 900°C, while that of the S—O distances increases. Inspection employing the O'Keeffe-Voronoi polyhedron constructed around Ba reveals a change in coordination character above 900°C. The results suggest that a premonitory movement of the atoms begins at temperatures between 900°C and 1000°C and the final transition is triggered by excessively strained arrangements of the atoms within the structure.