Effect of the grain boundary on the dielectric breakdown strength of (Ba0.4Sr0.6)TiO3 paraelectric ceramics with various grain sizes

(Ba_0.4Sr_0.6)TiO₃ (BST) paraelectric ceramics (T_c ≈ -67 °C) with various grain sizes (0.6-1.8 μm) were synthesized by oxalate co-precipitation method and prepared by conventional solid-state sintering process. With decreasing grain sizes, the dielectric breakdown strength increases gradually. Based on the conductivity activation energy analysis, it was found that the larger grain boundary density plays a dominant role in controlling dielectric breakdown strength for samples with smaller grain sizes (1.0 to 0.6 μm). While with the growth of grain sizes above 1.0 μm, the sharply decreasing dielectric breakdown strength is induced by a combined effect of lower grain boundary density and more intensive interface polarization.