Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Aminoguanidinium hexafluorozirconate: a new ferroelectric (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 47-54 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: 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 CN4H8ZrF6 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 Tc = 383 (1) K. At this temperature, the heat capacity Cp exhibits an entropy change of 0.7 (1) J mol−1 K−1, while the relative permittivity εr exhibits an inflection and the dielectric loss a distinct peak; the dielectric anomaly at Tc 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 〈 Tc but not at T ≥ Tc; the prediction of ferroelectricity is hence confirmed. The value of the spontaneous polarization Ps is 0.45 (9) × 10−2 C m−2 at 298 K, with piezoelectric coefficient d33 = 1.9 (5) pC N−1 and pyroelectric coefficient p3 = 4 (1) µC m−2 K−1. Tilts of less than ∼11° by the two symmetry-independent CN4H{}_{8}^{2+} ions, combined with rotations of ∼20° or less by the N—NH3 and C—(NH2)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{}_{6}^{2-} anions also result in mirror symmetry, satisfying the structural criteria required for the development of ferroelectricity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889800015508
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Anhydrous ammonioguanidinium(2+) and dihydrated bis[aminoguanidinium(1+)] hexafluorosilicates: new co-products of preparing ferroelectric ammonioguanidinium(2+) hexafluorozirconate. Erratum (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 626-626 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An error in printing is reported. In the paper by Ross et al. [Acta Cryst. (1999), B55, 246–254] the length of a bond formed by H3 is given incorrectly in the sixth sentence of the first paragraph of §3.3 on page 251. The sentence should read `The out-of-plane displacement modifies the hydrogen-bonding pattern, allowing an approach of 2.21 (2) Å to F2, see Table 4; the resulting increase in structural stability supports this model.'
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768199006679
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Anhydrous ammonioguanidinium(2+) and dihydrated bis[aminoguanidinium(1+)] hexafluorosilicates: new co-products of preparing ferroelectric ammonioguanidinium(2+) hexafluorozirconate (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 246-254 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Ammonioguanidinium hexafluorosilicate, CH8N_4^{2+}·SiF_6^{2-}, and bis(aminoguanidinium) hexafluorosilicate dihydrate, 2CH7N_4^+·SiF_6^{2-}·2H2O, are new materials formed as by-products in course of preparing ferroelectric CH8N4ZrF6 in the presence of glassware. Their structures were determined for comparison with the corresponding hexafluorozirconates. All atoms including the eight H atoms in the CH8N_4^{2+} cation and the seven H atoms in the CH7N_4^+ cation have been located and refined with wR(F2) = 0.0653, R = 0.0255, S = 1.146 and wR(F2) = 0.0745, R = 0.0301, S = 1.065, respectively. The N2C—N—N backbone of the 2+ cation is close to planarity, while that of the 1+ cation does not differ significantly from planarity. The SiF_6^{2-} octahedron is nearly ideally regular in both materials, with 〈Si—F〉 = 1.684 (unbiassed estimator of standard uncertainty = 0.016) Å in the anhydrous hexafluorosilicate and 1.6801 (unbiassed estimator of standard uncertainty = 0.0006) Å in the dihydrate. The combination of coulombic and NH...F interactions in CH8N4SiF6 results in a relatively dense variant of the NaCl structure. In addition to similar forces, the dihydrate is also characterized by the role of the water molecule with its strong NH...O interactions; its packing efficiency is, however, appreciably less than that of the anhydrous hexafluorosilicate with an ∼8% increase in void space. Cleaved crystals of the dihydrate are frequently twinned across the (001) composition plane, with a twofold rotation about the b axis as the twin operation.The systematic names of the compounds studied in this paper are given following IUPAC recommendations. The corresponding fluorozirconates have previously been referred to in the literature by the non-IUPAC names aminoguanidinium(2+) hexafluorozirconate and diaminoguanidinium(1+) hexafluorozirconate for ammonioguanidinium(2+) hexafluorozirconate and bis[aminoguanidinium(1+)] hexafluorozirconate, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768198013044
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...