STRUCTURAL PHASE-TRANSITION IN LA-SUBSTITUTED PB[(YB1 2NB1/2)(0.88)TI-0.12]O-3 RELAXOR SYSTEM/

We have investigated the effect of substitution of La2O3 + Yb2O3 to th e perovskite solid solution near the composition (PbYb1/2Nb1/2O3)(0.88 )-(PbTiO3)(0.12) in the chemical formula (1-x)[(PbYb1/2Nb1/2O3)(0.88) (PbTiO3)(0.12)]-xLaYbO(3). When x = 0.0 and x = 0.01; these solid solu tion have partially disordered pseudocubic structure and behave as a f erroelectric relaxer. For x greater than or equal to 0.02, the charact er of phase transition changes from a ferroelectric relaxer type to an antiferroelectric one and the transition temperature surprisingly inc reases with LaYbO3 addition. In this composition range, the solid solu tion displays a sharp antiferroelectric transition. The effect on the tendency toward antiferroelecticity with increasing LaYbO3 content is displayed in restoring of the superlattice reflections due to antiferr oelectric order. From the structural study of ceramic specimen having various PbTiO3 and LaYbO3 concentration, we have constructed a portion of phase diagram of pseudoternary PbYb1/2Nb1/2O3-PbTiO3-LaYbO3 system .