Influence of Boron Doping on the Dielectric Characteristics of Eu3+-Doped β-SrTa2O6 and Eu3+-Doped BaTa2O6 Tungsten Bronze-Type Ceramics

The effect of boron doping on dielectric properties was examined using beta-SrTa2O6:xEu(3+) (x = 1.5 mol%, 3 mol%, 5 mol%, 10 mol%), beta-SrTa2O6:xEu(3+), yB(3+) (x = 1.5 mol%, 3 mol%, 5 mol%, 10 mol%, y = 10 mol%) and BaTa2O6:xEu(3+), yB(3+) (x = 10 mol%, y = 0 mol%, 5 mol%, 15 mol%, 30 mol%, 50 mol%, 70 mol%, 100 mol%) tungsten bronze ceramics produced by the solid-state reaction method. X-ray diffraction (XRD ) results of all the beta-SrTa2O6 and BaTa2O6 samples showed that they retained a single-phase structure. In scanning electron microscopy (SEM) examinations, the presence of boron promoted grain growth and agglomeration in the beta-SrTa2O6 grains, while the increased boron concentration led to grain elongation in addition to grain growth in the BaTa2O6 grains. The dielectric results for the beta-SrTa2O6:xEu(3+) and beta-SrTa2O6:xEu(3+), yB(3+) series showed that increased Eu3+ caused a decrease in the dielectric constant (epsilon ') and dielectric loss (tan delta), whereas the increasing B3+ presence for the BaTa2O6:xEu(3+), yB(3+) series led to an increase in the dielectric constant and a decrease in dielectric loss. The increase in tetragonality for BaTa2O6:xEu(3+), yB(3+) ceramics was correlated with a higher ferroelectric Curie temperature.