Low temperature ferroelastic phase transition in K ₃ Na(CrO ₄ ) ₂

Abstract

Abstract Dielectric, thermal and elastic properties of K3Na(CrO4)2 crystals, grown from aqueous solution at 315 K, were studied in the temperature range from 100 to 300 K. The studied properties were found to exhibit anomalous temperature behaviour. At 239 K a structural transition to the ferroelastic phase was observed. The ferroelastic character of this new phase was confirmed by direct observation of the domain structure reorientable under the effect of appropriate mechanical stress, and by a strong decrease in the torsion vibration frequencies related to the acoustic phonon softening. The morphology of the crystal studied and the lack of pyroelectric and piezoelectric properties together with the analysis of the domain structure observed in the polarized light for crystal plates oriented perpendicularly to the main crystallographic directions, lead to the conclusion that, at 239 K, K3Na(CrO4)2 undergoes a ferroelastic phase transition from the trigonal point group 3m to the monoclinic 2/m one.