The alternating-current conductivity between 293 and 743K was 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 were characterized. The latter was shown to be accompanied by a higher F-ion mobility above 368K. A new dielectric anomaly which was observed isochronously at 670K corresponded to an expected, but previously unobserved, transition from phase-II to the paraelectric prototype, phase-I.

J.M.Réau, A.Simon, M.E.Omari, J.Ravez: Journal of the European Ceramic Society, 1999, 19[6-7], 777-9