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

Area of Science:

• Solid State Physics
• Materials Science
• Crystallography

Background:

• Ferroelectricity in ceramic materials is crucial for electronic applications.
• Understanding the mechanisms and temperature dependence of ferroelectric properties is key to material design.
• Lawsonite, a calcium aluminum silicate mineral, has recently shown potential ferroelectric properties.

Purpose of the Study:

• To investigate the ferroelectric hysteresis of ceramic lawsonite.
• To determine the temperature dependence of its remanent polarization.
• To elucidate the nature and driving mechanism of the ferroelectric phase transition in lawsonite.

Main Methods:

• Ferroelectric hysteresis measurements on ceramic lawsonite.
• Analysis of temperature-dependent remanent polarization (P(r)).
• Thermodynamic analysis of the phase transition (Pmcn-P 2(1)cn) using the order parameter (Q).

Main Results:

• Remanent polarization P(r) exhibits a temperature dependence described by P(r) = P(o)Θ(s)(cothΘ(s)/T - cothΘ(s)/T(c)) with Θ(s) = 26 K.
• The observed almost linear temperature evolution of P(r) indicates improper ferroelectricity.
• The Curie temperature (T(c)) was determined to be 124 K, and the phase transition is strictly continuous.

Conclusions:

• The ferroelectricity in lawsonite ceramics is confirmed to be improper.
• Hydrogen ordering is identified as the primary driving mechanism for the ferroelectric phase transition.
• The findings provide insights into the fundamental properties of ferroelectric phase transitions in silicate minerals.