$Ba_{1-x}Sr_xTiO_3$ ceramics have widely been investigated for application of PTCR, phase shifter, high voltage capacitor, etc. Among them, $Ba_{0.67}Sr_{0.33}TiO_3$ (BST67/33) is a promising material for thermal imaging under a DC-bias field, i.e. "Dielectric Bolometer".
In this study, the grain size of sintered BST67/33 could be changed by using various heating rates and sintering temperatures and its effect on dielectric and pyroelectric properties were measured. In the studied range, the dielectric constant increased with decreasing grain size probably because of the reduction o 90˚ domains in grains, as in the case of $BaTiO_3$ ceramics. Reduction of 90˚ domains in grains increases the internal stresses in the interior of grains("Internal Stress Model"). The pyroelectric current increased as DC bias field increased up to 2kV/cm. Above 2kV/cm, the pyroelectric current decreased, but its peak around $T_c$ was broadened. The smaller the grain size was, the higher the pyroelectric current peak was under same DC bias field.
