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Thermal expansion of deuterated hopeite, Zn3(PO4)2·4D2O

  • Paul F. Schofield EMAIL logo , Kevin S. Knight , Mark E. Hodson and Anna M. Lanfranco
From the journal American Mineralogist

Abstract

The lattice parameters extracted from Lebail analysis of neutron powder diffraction data collected between 2 and 300 K have been used to calculate the temperature evolution of the thermal expansion tensor for hopeite, Zn3(PO4)2·2H2O, Pnma, Z = 4 with a = 10.6065(4) Å, b = 18.2977(4) Å, c = 5.0257(2) Å at 275 K. The a lattice parameter shows a negative thermal expansion, the b lattice parameter appears to saturate at 275 K while the c lattice parameter has a more typical positive thermal expansion. At 275 K, the magnitudes of the thermal expansion coeficients are αa = -1.1(4) × 10-5 K-1, αb = 2.4(9) × 10-6 K-1 and αc = 3.6(2) × 10-5 K-1. Under the conditions of these experiments, hopeite begins to dehydrate to the dihydrate between 300 and 325 K, and between 480 and 500 K the monohydrate is formed. The thermal expansion of the dihydrate has been calculated between 335 and 480 and at 480 K the magnitudes of the thermal expansion coeficients are αa = 1(2) × 10-5 K.1, αb = 4(1) × 10-6 K-1, αc = 4(2) × 10-5 K-1, αβ= 1(1) × 10-5 K-1, and αV = 2(2) × 10-5 K-1. The thermal expansion of hopeite is described in terms of its crystal structure and possible dehydration mechanisms for the α and β modifications of hopeite are discussed.

Received: 2005-9-21
Accepted: 2007-2-19
Published Online: 2015-4-1
Published in Print: 2007-7-1

© 2015 by Walter de Gruyter Berlin/Boston

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