Omari, M.El. and Réau, J.-M. and Sénégas, J. and Ravez, J. and Abrahams, S.C. and Nadiri, A. and Yacoubi, A. (1998) Characterization of four phase transitions in Pb5AI3F19, including a new transition at 670 K, by impedance and NMR spectroscopy. Journal of Chemical Physics, 108 (7). pp. 2896-2902.

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Abstract

The ac (alternating current) conductivity of Pb5Al3F19 between 293 and 743 K has been analyzed within a combined complex impedance, modulus, and permittivity formalism. The antiferroelectric phase IV to ferroelastic phase III, and the phase III to paraelastic phase II, transitions have been characterized; the latter is shown to be accompanied by higher F- ion mobility above T= 368 ±5 K. A new dielectric anomaly observed isochronously in ε′ (f,T) at 670 K corresponds to an expected, but hitherto unobserved, transition from phase II to the paraelectric prototype phase I of Pb5Al3F19. A 19F NMR investigation between 125 and 430 K of F- ion diffusion properties in Pb5Al3F19 shows that half the anions have become mobile at the ferroelectric phase V to phase IV transition temperature and that almost all the anions are mobile at the phase IV to phase III transition temperature. These motions are shown to be short range, and no correlation is found between phase formation and F- ion diffusion properties in Pb5Al3F19 in the temperature range below 320 K. © 1998 American Institute of Physics.

Item Type: Article
Uncontrolled Keywords: Activation energy; Characterization; Electric conductivity measurement; Ions; Lattice constants; Nuclear magnetic resonance spectroscopy; Numerical methods; Phase transitions; Polycrystalline materials; X ray diffraction analysis, Frequency response analyzer; Impedance spectroscopy; Ion diffusion properties, Lead compounds
Subjects: Chemistry
Divisions: SCIENTIFIC PRODUCTION > Chemistry
Depositing User: Administrateur Eprints Administrateur Eprints
Last Modified: 31 Jan 2020 15:45
URI: http://eprints.umi.ac.ma/id/eprint/2103

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