Preparation and characterisation of Pb(Fe1/2Ta1/2)O-3 relaxor ferroelectric

The reaction sequences between the oxides at various calcining temperatures were examined through the identification of the reaction products. Formati on of pyrochlore phase with tetragonal symmetry is a required preparatory s tep for subsequent generation of perovskite phase. Most of the pyrochlore p hase turns into the perovskite phase in the temperature range of 700-800 de grees C and this conversion persists up to 950 degrees C. The double calcin ation approach seems infeasible in promoting the pyrochlore to perovskite t ransformation 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 m aximum exhibits high value (epsilon'(max) = 17 500 at 248 K at 100 Hz). The distinct relaxer behaviour along with the further enhanced permittivity va lues for the annealed specimen reveal that the annealing treatment is mainl y 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.