Improper ferroelectricity in lawsonite CaAl2Si2O7(OH)2·H2O: hysteresis and hydrogen ordering

• Published in: Journal of physics. Condensed matter Vol. 23; no. 22; p. 222202
• Main Authors: Salje, E K H, Crossley, S, Kar-Narayan, S, Carpenter, M A, Mathur, N D
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 08.06.2011; Institute of Physics
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Dielectric loss and relaxation; Dielectric properties of solids and liquids; Dielectrics, piezoelectrics, and ferroelectrics and their properties; Domain structure; hysteresis; Exact sciences and technology; Ferroelectricity and antiferroelectricity; Physics; Aluminium Calcium Hydroxosilicates Mixed; Dielectric susceptibility; Curie point; Phase transformations; Temperature effects; Dielectric losses; Scaling laws; Order parameters; Spontaneous polarization; Hydrates; Ferroelectric hysteresis
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/23/22/222202

Ferroelectric hysteresis measurements on ceramic lawsonite show a temperature dependence of the remanent polarization P(r) = P(o)Θ(s)(cothΘ(s)/T - cothΘ(s)/T(c)) ∼ Q(2), Θ(s) = 26 K, where Q is the thermodynamic order parameter of the phase transition Pmcn-P 2(1)cn. This almost linear temperature evolution of P(r) proves the improper nature of ferroelectricity in lawsonite. The Curie temperature is T(c) = 124 K. The phase transition is strictly continuous, with a weak conjugated field near the transition point, and hydrogen ordering is discussed as the primary driving mechanism.