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.