Thermally activated proton hopping in lawsonite, the ferroelectric transition at 125 K, and the co-elastic phase transition at 270 K

摘要: Lawsonite, CaAl2Si2O7(OH)2H2O, is a novel ferroelectric material which dominated by ordering and disordering of protons. We report related elastic anomalies in lawsonite. A new approach to extracting acoustic data from resonant ultrasonic spectroscopy has been applied investigate the This based on analysis entire spectra, rather than more conventional fitting individual resonance peaks captures three features transitions. Firstly, structural disorder protons persists down low temperatures. Secondly, transition between two paraelectric phases near 270 K mainly order/disorder type but not directly coupled proton mobility. Thirdly, at 125 shows direct link with mobility an activation energy 0.03 eV. The latter occurs large class crystals where molecular groups are linked hydrogen its thermodynamic potential almost identical that KDP (KH2PO4), albeit smaller isotope effect. While some damping seen small temperature intervals below points, these much those occur ferroelastic phase