Effects of the sinterization process and the influence of the lanthanum content in the Sr0.3-3Y/2LaYBa0.7Nb2O5 ceramic system

Abstract

A study of the dielectric properties of the lanthanum doped Sr0.3Ba0.7Nb2O6 (SBN30) ceramic according to the stoichiometric formulation Sr0.3-3y/2LayBa0.7Nb2O6 with y = 0.01, 0.03 and 0.05, and the influence of the sintering conditions are reported. The XRD shows single phase compounds for Sr0.285La0.01Ba0.07Nb2O6, (LSBN1) and Sr0.255La0.03Ba0.7Nb2O6 (LSBN3) ceramics, both samples having similar microstructure, densification and dielectric properties. The density increases linearly with Lnt, where t is the sintering time, and the values of the maximum ferroelectric peaks of the permitivity rise steadily with t. Using the Bruggeman model to estimate the theoretical permitivity, it is concluded that the magnitude of the experimental permitivity peaks are mainly affected by the volume fraction of porosity of the samples. In this study we also establish that pores diffusion mechanisms behave according to the Ginstling-Brownshten equation. For Sr0.225La0.05Ba0.7Nb2O6 (LSBN5) sample, XRD analysis reveals the presence of isostructural compounds of the intermediate phases BaNb2O6 and SrNB2O6, and the dielectric properties start to deteriorate. This fact indicates the existence of a solubility limit of the Lanthanum ions in the SBN solid solution.