New Ferroelectric Aminoguanidinium Hexafluorozirconate
Abstract
Satisfaction of structural criteria led to the prediction that anhydrous aminoguanidinium hexafluorozirconate CN_4H_8ZrF6 is a new ferroelectric. Calorimetric and dielectric permittivity measurements reveal a highly-reproducible anomaly at the Curie temperature Tc = 383(1) K. The heat capacity undergoes an entropy change of 0.7(1) J mol-1 K-1 at Tc as the relative permittivity increases sharply by nearly an order of magnitude. Dielectric hysteresis at 295 K under the application of 1 MV m-1 ac is also observed at all T < Tc but not at T > T_c, confirming the prediction. Saturation is not reached before electric breakdown above 1 MV m-1 ac. The piezoelectric coefficient d_33 = 1.9 pC N-1 at 298 K. Polarisation reversal requires each symmetry-independent CN_4H_8^+2 ion to tilt and both N NH3 and C (NH_2)2 groups to rotate about the C N bond. Small atomic displacements within the ZrF_6-2 anion lead to mirror symmetry in course of the phase transition.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2000
- Bibcode:
- 2000APS..MARP21002B