Aminoguanidinium hexafluorozirconate: a new ferroelectric

Analysis of the atomic arrangement in anhydrous aminoguanidinium hexafluorozirconate, CN4H8ZrF6, reported by Bukvetskii, Gerasimenko & Davidovich [Koord. Khim.(1990),16, 1479–1484], led to the prediction that it is a new ferroelectric [Abrahams, Mirsky & Nielson (1996).Acta Cryst.B52, 806–809]. Initial attempts to verify the prediction were inconclusive because of the variety of closely related materials produced under the original preparation conditions. Clarification of these conditions led to the formation of pure CN4H8ZrF6and the growth of single crystals with dimensions as large as 7 × 7 × 2 mm. Highly reproducible calorimetric and dielectric permittivity anomalies reveal the Curie temperatureTc= 383 (1) K. At this temperature, the heat capacityCpexhibits an entropy change of 0.7 (1) J mol−1 K−1, while the relative permittivity ∊rexhibits an inflection and the dielectric loss a distinct peak; the dielectric anomaly atTcis observed only at the lowest (0.1–1 kHz) frequencies used. Dielectric hysteresis is demonstrable at 295 K under the application of ∼1 MV m−1alternating fields and remains observable at allT