The thermal expansion and crystal structure of mirabilite (Na2SO4 center dot 10D(2)O) from 4.2 to 300 K, determined by time-of-flight neutron powder diffraction.
Physics and Chemistry of Minerals
We have collected high resolution neutron powder diffraction patterns from Na2SO4 center dot 10D(2)O over the temperature range 4.2-300 K following rapid quenching in liquid nitrogen, and over a series of slow warming and cooling cycles. The crystal is monoclinic, space-group P2(1)/c (Z = 4) with a = 11.44214(4) angstrom, b = 10.34276(4) angstrom, c = 12.75486(6) angstrom, beta = 107.847(1)degrees, and V = 1436.794(8) angstrom(3) at 4.2 K (slowly cooled), and a = 11.51472(6) angstrom, b = 10.36495(6) angstrom, c = 12.84651(7) angstrom, beta = 107.7543(1)degrees, V = 1460.20(1) angstrom(3) at 300 K. Structures were refined to R-P (Rietveld powder residual, R-P = Sigma vertical bar I-obs - I-calc vertical bar/Sigma I-obs) better than 2.5% at 4.2 K (quenched and slow cooled), 150 and 300 K. The sulfate disorder observed previously by Levy and Lisensky (Acta Cryst B34:3502-3510, 1978) was not present in our specimen, but we did observe changes with temperature in deuteron occupancies of the orientationally disordered water molecules coordinated to Na. The temperature dependence of the unit-cell volume from 4.2 to 300 K is well represented by a simple polynomial of the form V = -4.143(1) x 10(-7) T-3 + 0.00047(2) T-2 - 0.027(2) T + 1437.0(1) angstrom(3) (R-2 = 99.98%). The coefficient of volume thermal expansion, alpha(V), is positive above 40 K, and displays a similar magnitude and temperature dependence to alpha(V) in deuterated epsomite and meridianiite. The relationship between the magnitude and orientation of the principal axes of the thermal expansion tensor and the main structural elements are discussed; freezing in of deuteron disorder in the quenched specimen affects the thermal expansion, manifested most obviously as a change in the behaviour of the unit-cell parameter beta.
|Title:||The thermal expansion and crystal structure of mirabilite (Na2SO4 center dot 10D(2)O) from 4.2 to 300 K, determined by time-of-flight neutron powder diffraction|
|Keywords:||Mirabilite, Sodium sulfate decahydrate, Thermal expansion, Neutron diffraction, SODIUM-SULFATE DECAHYDRATE, PHASE-TRANSITIONS, GLAUBERS SALT, X-RAY, CRYSTALLIZATION, THERMODYNAMICS, HEPTAHYDRATE, EQUILIBRIA, EUROPA, ORIGIN|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Earth Sciences|
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