Highlights on the reversible nonpolar-to-polar P3121-P31 phase transition at low temperature in NaLa(SO4)2·H2O: mechanism and piezoelectric properties.

Abstract

We report the existence in NaLa(SO4)2·H2O of a displacive phase transition under 200 K from the nonpolar P3121 to the polar P31 space group. This phase transition was predicted by density functional theory based calculations and experimentally confirmed from infrared spectroscopy and X-ray diffraction. The A2 polar irreducible representation is the primary order parameter. The structural water and hydrogen bonding are the mechanism driving the phase transition. The piezoelectric properties of this new P31 phase have been investigated by first principles based calculations. The highest piezoelectric-strain constants in the zero Kelvin limit are predicted for the d12 and d41 elements with values about 3.4 pC N-1. This compound could be interesting as piezoelectric actuator for cryogenic applications.