Ferroelectric random access memory (FeRAM) is expected to be the next generation memory. PbZr_xTi_1−xO₃ (PZT) is considered as a candidate because of its high remanent polarization (P_r). We investigated the relation between physical properties, crystal structure and ferroelectric performance of the sample before and after various heat treatments. From the results, remanent polarization (P_r) and coercive field (E_c) increased with increasing P_O2 during heat treatment. The remanent polarization (P_r) and coercive field (E_c) decreased with increasing Zr content x. Furthermore, the dielectric constants at room temperature increased with increasing Zr content x. On the other hand, Curie Temperature (T_C) increased with decreasing Zr content x or increasing P_O2 during heat treatment. From the structural analysis, the bond length of M(Zr,Ti)-O1 decreased with increasing P_O2 during heat treatment or with decreasing Zr content x of pre-heated samples. Consequently, the ferroelectric performance was affected by changing the defect of oxygen and the strain of the structure.