Acoustic dissipation associated with phase transitions in lawsonite, CaAl2Si2O7(OH)2.H2O

McKnight, R. E. A. and Carpenter, M. A. and Darling, T. W. and Buckley, A. and Taylor, P. A. (2007) Acoustic dissipation associated with phase transitions in lawsonite, CaAl2Si2O7(OH)2.H2O. American Mineralogist, 92 (10). pp. 1665-1672. ISSN 0003-004X DOI

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Resonant ultrasound spectra of a single crystal and a polycrystalline sample of lawsonite [CaAl2Si2O7(OH)2·H2O] have been measured at room temperature and at low temperatures in the region 20–300 K. The infl uence of known phase transitions at 125 and 270 K is seen in the frequency variations of the resonance peaks, which are indicative of elastic stiffening, and in values for the quality factor QQF, which are indicative of dissipation. Two dissipation peaks, at ~250 and ~210 K, are interpreted as being due to the proton order-disorder processes associated with the two species of hydrogen atoms in the structure: one in hydroxyl OH groups and one in the H2O molecules. These occur below the Cmcm ↔ Pmcn transition point but coincide with changes in the shear elastic constants and in features of IR spectra reported elsewhere. A third, much smaller, dissipation peak occurs immediately below the Pmcn ↔ P21cn transition point. The combination of these anomalies in acoustic dissipation and in elastic constants is consistent with the view that the Cmcm ↔ Pmcn transition is driven both by displacive and proton ordering effects. For the Pmcn ↔ P21cn transition, dissipation and the transition are more closely related, consistent with the view that the transition is driven essentially by proton ordering.

Item Type: Article
Uncontrolled Keywords: 2007 AREP IA55 2007 P
Subjects: 03 - Mineral Sciences
Divisions: 03 - Mineral Sciences
Journal or Publication Title: American Mineralogist
Volume: 92
Page Range: pp. 1665-1672
Identification Number:
Depositing User: Sarah Humbert
Date Deposited: 16 Feb 2009 13:03
Last Modified: 23 Jul 2013 10:07

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