Grain-size-insensitive dielectric properties of Sr_0.6Ba_0.4Nb₂O₆ relaxor ferroelectric ceramics with tetragonal tungsten bronze structure

The influence of grain size on the dielectric properties of Sr_0.6Ba_0.4Nb₂O₆ (SBN60) ceramics with a tetragonal tungsten bronze structure was examined. The conventional and two-step sintering procedures were used to fabricate dense and phase-pure SBN60 ceramics with grain sizes ranging from 2.2 μm to 17.3 μm. In the temperature dependence of the dielectric permittivity, all samples showed a relaxor-like broad dielectric peak with a maximum at around 60 °C. The maximum dielectric permittivity and dielectric maximum temperature of the SBN ceramics were found to be less dependent on the grain size. The reason for the grain-size-insensitive dielectric properties of the SBN60 ceramics is discussed based on the analysis of the dielectric properties and Raman spectra.