Lead zirconate titanate (PZT) ceramics are the most widely used commercial piezoelectric ceramics. However, the relationships between structure and properties are still not completely clarified. In this work, a broad investigation is carried out on commercial PZT 5A, 5H and 4D ceramics. X-ray diffraction revealed that these compounds mainly contain a mixture of P4mm and C1m1 phases at room temperature, and poling induces an increased unit cell distortion in both phases and a higher content of the monoclinic phase. In the poled samples, the Curie point shifts towards lower temperatures, contradicting the Abrahams-Kurtz-Jamieson (AKJ) relation for distorted displacive ferroelectrics. The discordance in the phase transition behavior can be attributed to the decreased domain wall density in the PZT systems. Furthermore, the observed increase of the dielectric permittivity from radiofrequency to the THz range is explained by the increase of the ferroelectric distortion associated with the field-induced transitions and decreased domain wall density. A parameter ψ was introduced to characterize the asymmetry of ferroelectric hysteresis loops. The higher ψ value of the hard PZT 4D ceramic compared to that of soft PZT 5A and 5H is attributed to the pinning effect of oxygen vacancies on domain walls.