Dielectric properties of La3+ doped Sr0.3-3y/2LayBa0.7Nb2O6 ceramics prepared under different sintering conditions

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 is reported. The XRD shows single phase compounds for Sr0.285La0.01Ba0.7Nb2O6 (LSBN1) and Sr0.255La0.03Ba0.7Nb2O6 (LSBN3) ceramics, both samples having similar microstructure, densification and dielectric properties. The density increases linearly with ln t, where t is the sintering time, and the values of the maximum ferroelectric peaks of the permittivity increase steadily with t. Using the Bruggeman model to estimate the theoretical permittivity, it is concluded that the magnitude of the experimental permittivity peaks are mainly affected by the volume fraction of porosity of the samples. In this study we also establish that pore diffusion mechanisms behave according to the Ginstling-Brownshtein equation. For the 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 Lanthanum ions in the SBN solid solution.