Impedance spectroscopy analysis of Pb5Al3F19

The ac conductivity of Pb5Al3F19 between 293 and 743 K has been analyzed wi thin a combined complex impedance, modulus and permittivity formalism. The antiferroelectric phase IV to ferroelastic phase III, and the phase III to paraelastic phase If, transitions have been characterized; the latter is sh own to be accompanied by higher F- ion mobility above T = 368 +/- 5 K. A ne w dielectric anomaly observed iso-chronously in epsilon' (f, T) at 670 K co rresponds to an expected, but hitherto unobserved, transition from phase II to the paraelectric prototype phase I of Pb5Al3F19. (C) 1999 Elsevier Scie nce Limited. All rights reserved.