Order-parameter coupling in the improper ferroelectric lawsonite

Salje, E. K. H. and Gofryk, K and Safarik, D J and Lashley, J C (2012) Order-parameter coupling in the improper ferroelectric lawsonite. Journal of Physics: Condensed Matter, 24 (25). p. 255901. DOI https://doi.org/10.1088/0953-8984/24/25/255901

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Abstract

Low-temperature specific heat and thermal expansion measurements are used to study the hydrogen-based ferroelectric lawsonite over the temperature range 1.8 K ≤ T ≤ 300 K. The second-order phase transition near 125 K is detected in the experiments, and the low-temperature phase is determined to be improper ferroelectric and co-elastic. In the ferroelectric phase T ≤ 125 K, the spontaneous polarization Ps is proportional to (1) the volume strain es, and (2) the excess entropy ΔSe. These proportionalities confirm the improper character of the ferroelectric phase transition. We develop a structural model that allows the off-centering of hydrogen positions to generate the spontaneous polarization. In the low-temperature limit we detect a Schottky anomaly (two-level system) with an energy gap of Δ ~ 0.5 meV.

Item Type:	Article
Uncontrolled Keywords:	2012AREP; IA64;
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences
Journal or Publication Title:	Journal of Physics: Condensed Matter
Volume:	24
Page Range:	p. 255901
Identification Number:	https://doi.org/10.1088/0953-8984/24/25/255901
Depositing User:	Sarah Humbert
Date Deposited:	18 Jul 2012 23:06
Last Modified:	23 Jul 2013 10:04
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2566

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