Crossover from classical to 3d-Ising critical behaviour near the antiferrodistortive phase transition of lawsonite.

Schranz, W. and Troster, A. and Gardon, M. and Krexner, G. and Prem, M. and Carpenter, M. A. and Sondergeld, P. and Armbruster, T. (2005) Crossover from classical to 3d-Ising critical behaviour near the antiferrodistortive phase transition of lawsonite. Zeitschrift für Kristallographie, 220 (8). pp. 704-711.

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Abstract

Results of X-ray scattering intensities and peak profiles of lawsonite single crystals are presented in a wide temperature range including the antiferrodistortive phase transition Cmcm - (Tc 270 K) → Pmcn. In the integrated intensities of the superlattice reflections above Tc pronounced pretransitional tails similar to those detected recently in birefringence [P. Sondergeld et al., Phys. Rev. B62, 6143 (2000)] and in excess entropy data [S. A. Hayward et al., Eur. J. Min. 14, 1145 (2002)] are observed. These tails correspond to diffuse Lorentzian shaped scattering peaks. The temperature variation of the diffuse scattering intensity and profile can be well described within a Landau-Ginzburg model. In combination with entropy data we obtain a complete set of free energy parameters. Using these coefficients we are able to fit the spontaneous part and the precursor tails of the integrated intensities, the excess birefringence and entropy in a broad temperature range outside a temperature interval of about ±3 K around Tc. In the vicinity of Tc the experimental data are in excellent agreement with the predictions of a crossover model, the effective critical exponent αeff(τ) varying from the classical (αeff = 0.5) to the 3d Ising limit (αeff = 0.11). Lawsonite therefore represents an ideal system to study the crossover from classical to critical behavior.

Item Type:	Article
Additional Information:	0044-2968 Monthly: 9-14 issues per year Germany English
Uncontrolled Keywords:	2005 AREP IA49 2005 P
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences
Journal or Publication Title:	Zeitschrift für Kristallographie
Volume:	220
Page Range:	pp. 704-711
Depositing User:	Sarah Humbert
Date Deposited:	18 Aug 2010 15:23
Last Modified:	23 Jul 2013 09:59
URI:	http://eprints.esc.cam.ac.uk/id/eprint/1813

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