Ferroelectric behavior and phase transitions in the SrA1F5family

The atomic arrangement in polar SrA1F5 is related to that in an identical structure but opposite polarity by means of atomic displacements no greater than about 0.5Å. Such displacements reverse the spontaneous polarization and lead to a predicted ferroelectric-paraelectric phase transition temperature of 685K. A specific heat anomaly is observed at about 695K and the dielectric constant exhibits an anomaly at about 715K. The piezoelectric d33 coefficient varies from sample to sample, in the range 0.1 < d33 < 0.8 pC N−1. The properties of SrA1F5 are hence those of a new ferroelectric material. Nine members of the AIIBIIIF5 family have been identified, with A = Sr and B = Al, Cr, Ga; A = Ba and B = Ti, V, Fe; A = Pb and B = Al, Ga; and EuA1F5. The phase transition temperature is a function of the A2+ and B3+ ionic radii.