$0.10Pb(Sb_{1/2}Sn_{1/2})O_3-0.25PbTiO_3-0.65PbZrO_3$ specimens doped with $ MnO_2;(0.18;mol\%)$ and $Y_2O_3;(0~0.4;wt\%)$ were fabricated by the mixed-oxide method. All specimens showed the typical XRD patterns of a perovskite polycrystalline structure and the lattice constant decreased with increasing amount of $Y_2O_3$. The relative dielectric constant and the dielectric loss of the specimens doped with $0.2;wt\%;Y_2O_3$ were 704 and 0.0201, respectively. The remanent polarization, the coercive field and the pyroelectric coefficient of the specimen doped with $0.2;wt\%;Y_2O_3$ were $10.88 imes10^{-2}Cm^{-2},;11.12 imes10^2kVm^{-1}$ and $5.03 imes10^{-4}Cm^{-2}K^{-1}$ at $25^{circ}C$, respectively. The figures of merit, $F_V$ for the voltage responsivity and $F_D$ for the specific detectivity, of the specimen doped with $0.2;wt\%;Y_2O_3$ were the good values of $3.04 imes10^{-2};m^2C^{-1};and;1.50 imes10^{-5};Pa^{-1/2}$, respectively.