Influence of the Sintering Conditions on the Microstructural, Dielectric and Piezoelectric Properties of La Doped KNNTa Ceramics

Abstract

Two batches of lead free ceramics of the composition (K_0.5Na_0.5)_0.95La_0.016Nb_0.9Ta_0.1O₃ (KNNTaLa) were sintered between 1150 and 1180 °C. In the first batch, the samples were prepared in a sealed crucible embedded in powders of the same composition and, in the second, they were sintered in open air. Measurements made by X-ray diffraction, scanning electron microscopy and analysis of the phase transition and electromechanical response show, in general, a better performance for the encapsulated samples where very high values of density are obtained (about 97% of the theoretical density). La doping of KNNTa ceramics shifts its transition temperatures toward lower values, from 361 ºC to 317 ºC for the tetragonal-cubic (ferroelectricparaelectric) and from 187 °C to 150 °C for the orthorhombictetragonal (ferroelectric-ferroelectric) transitions in this particular composition. The obtained electromechanical parameters are reasonably good and show the potentiality of the KNNTaLa ceramic as a commercial piezoelectric material.