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Aminoguanidinium hexafluorozirconate: a new ferroelectric
Author(s) -
Bauer M. R.,
Pugmire D. L.,
Paulsen B. L.,
Christie R. J.,
Arbogast D. J.,
Gallagher C. S.,
Raveane W. V.,
Nielson R. M.,
Ross C. R.,
Photinos P.,
Abrahams S. C.
Publication year - 2001
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889800015508
Subject(s) - ferroelectricity , dielectric , pyroelectricity , curie temperature , materials science , analytical chemistry (journal) , permittivity , relative permittivity , condensed matter physics , heat capacity , piezoelectricity , dielectric loss , nuclear magnetic resonance , mineralogy , thermodynamics , chemistry , physics , composite material , optoelectronics , chromatography , ferromagnetism
Analysis of the atomic arrangement in anhydrous aminoguanidinium hexafluorozirconate, CN 4 H 8 ZrF 6 , 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. B 52 , 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 CN 4 H 8 ZrF 6 and the growth of single crystals with dimensions as large as 7 × 7 × 2 mm. Highly reproducible calorimetric and dielectric permittivity anomalies reveal the Curie temperature T c = 383 (1) K. At this temperature, the heat capacity C p exhibits an entropy change of 0.7 (1) J mol −1 K −1 , while the relative permittivity ɛ r exhibits an inflection and the dielectric loss a distinct peak; the dielectric anomaly at T c is 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 −1 alternating fields and remains observable at all T < T c but not at T ≥ T c ; the prediction of ferroelectricity is hence confirmed. The value of the spontaneous polarization P s is 0.45 (9) × 10 −2 C m −2 at 298 K, with piezoelectric coefficient d 33 = 1.9 (5) pC N −1 and pyroelectric coefficient p 3 = 4 (1) µC m −2 K −1 . Tilts of less than ∼11° by the two symmetry‐independent CN 4 H ions, combined with rotations of ∼20° or less by the N—NH 3 and C—(NH 2 ) 2 groups about the central C—N bond in each cation, as all H atoms rotate into or become symmetrically distributed about the planes at z = 0 or ½, allow them to conform to mirror symmetry via polar atomic displacements of ∼0.4 Å or less by N or C, and of 0.7 Å or less by H. Corresponding displacements of less than 0.08 Å within the two symmetry‐independent ZrF anions also result in mirror symmetry, satisfying the structural criteria required for the development of ferroelectricity.