Effects of the addition of $Nb_2O_5$ on the dielectric and electromechanical properties of $(Ba_{0.1} Pb_{0.9}) (Sn_{0.525} Ti_{0.475}) O_3$ system near the morphotropic phase boundary have been investigated.
The specimens were prepared by mixed oxide technique and atmosphere sintering method. The specimens were sintered at 1050℃, 1075℃, 1100℃, 1125℃, and 1150℃ for 1 hour in $O_2$ atmosphere.
With increasing amount of $Nb_2O_5$ accelerated deterioration of the sintered density was observed at specimens sintered at 1050℃. With the addition of $Nb_2O_5$ the dielectric constant and the dissipation factor increase but transition temperature was decreased. At the transition temperature the magnitude of the dielectric constant seemed to be proportional to the grain size, which was explained in terms of surface effect.
The dielectric constant and the dissipation factor after poling was lower than those of unpoled specimens. In the specimens with 0.32 wt.% $Nb_2O_5$ sintered at 1100℃ the planar coupling factor and the mechanical quality factor were 43% and 83 respectively.
