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Crystal structures and thermal expansion of alpha-MgSO4 and beta-MgSO4 from 4.2 to 300 K by neutron powder diffraction

Fortes, AD; Wood, IG; Vocadlo, L; Brand, HEA; Knight, KS; (2007) Crystal structures and thermal expansion of alpha-MgSO4 and beta-MgSO4 from 4.2 to 300 K by neutron powder diffraction. Journal of Applied Crystallography , 40 (4) 761 - 770. 10.1107/S0021889807029937. Green open access

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Abstract

Detailed neutron powder diffraction measurements have been carried out on two polymorphs of anhydrous magnesium sulfate, alpha-MgSO4 and beta-MgSO4. alpha-MgSO4 is orthorhombic, space group Cmcm (Z = 4); at 4.2 K the unit-cell dimensions are a = 5.16863 (3), b = 7.86781 (5), c = 6.46674 (5) angstrom, V = 262.975 (2) angstrom(3) [rho(calc) = 3040.16 (2) kg m(-3)], and at 300 K, a = 5.17471 (3), b = 7.87563 (5), c = 6.49517 (5) angstrom, V = 264.705 (2) angstrom(3) [rho(calc) = 3020.29 (2) kg m(-3)]. The axial and volumetric thermal expansion coefficients are positive at all temperatures and exhibit no unusual behaviour. Structures were refined at 4.2 and 300 K to R-P < 3%; less precise structural parameters were determined during warming from 4.2 to 300 K. beta-MgSO4 has a more complex structure, crystallizing in space group Pbnm (Z = 4); the unit-cell dimensions at 4.2 K are a = 4.73431 (8), b = 8.58170 (12), c = 6.67266 (11) angstrom, V = 271.100 (5) angstrom(3) [rho(calc) = 2949.04 (5) kg m(-3)], and at 300 K, a = 4.74598 (7), b = 8.58310 (10), c = 6.70933 (10) angstrom, V = 273.306 (4) angstrom(3) [rho(calc) = 2925.42 (4) kg m(-3)]. The thermal expansivities of the a and c axes, and the volumetric thermal expansion coefficient, are positive at all temperatures and normally behaved. However, the thermal expansion of the b axis is both very small and negative below similar to 125 K. Structural and thermal motion parameters for beta-MgSO4 as a function of temperature are also reported.

Type:Article
Title:Crystal structures and thermal expansion of alpha-MgSO4 and beta-MgSO4 from 4.2 to 300 K by neutron powder diffraction
Open access status:An open access version is available from UCL Discovery
DOI:10.1107/S0021889807029937
Publisher version:http://dx.doi.org/10.1107/S0021889807029937
Language:English
Additional information:Copyright © International Union of Crystallography Author(s) of this paper may load this reprint on their own web site or institutional repository provided that the cover page is retained. Republication of this article or its storage in electronic databases other than as specified above is not permitted without prior permission in writing from the IUCr.
Keywords:MAGNESIUM, TEMPERATURES, SULFATE, VOLCANISM, TENSOR
UCL classification:UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences

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