Preparation and characterisation of Pb(Fe1/2Ta1/2)O3 relaxor ferroelectric

The reaction sequences between the oxides at various calcining temperatures were examined through the identification of the reaction products. Formation of pyrochlore phase with tetragonal symmetry is a required preparatory step for subsequent generation of perovskite phase. Most of the pyrochlore phase turns into the perovskite phase in the temperature range of 700-800 degrees C and this conversion persists up to 950 degrees C. The double calcination approach seems infeasible in promoting the pyrochlore to perovskite transformation in the presence of excess lead oxide since the decomposition of the pyrochlore phase is a rather sluggish process. Sintered Pb(Fe1/2Ta1/2)O-3 displays ferroelectric relaxer behavior whose relative permittivity maximum exhibits high value (epsilon'(max) = 17 500 at 248 K at 100 Hz). The distinct relaxer behaviour along with the further enhanced permittivity values for the annealed specimen reveal that the annealing treatment is mainly characterized by the elimination of the pyrochlore phase rather than the formation of the ordering in the B-site cations. (C) 2000 Elsevier Science Ltd. All rights reserved.