title: Improper ferroelectricity in lawsonite CaAl2Si2O7(OH)2·H2O: hysteresis and hydrogen ordering.
abstract: 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.
authors.affiliation: Department of Earth Sciences, University of Cambridge, Cambridge, UK.
authors.forename: E K H
authors.initials: EK
authors.lastname: Salje
authors.forename: S
authors.initials: S
authors.lastname: Crossley
authors.forename: S
authors.initials: S
authors.lastname: Kar-Narayan
authors.forename: M A
authors.initials: MA
authors.lastname: Carpenter
authors.forename: N D
authors.initials: ND
authors.lastname: Mathur