An optimum TiO2 seed layer is said to facilitate nucleation and subsequent growth of perovskite phase in Pb(Zr,Ti)O-3 (PZT) films during annealing. The actual causes that prevent perovskite growth, particularly in sputtered PZT films on thick TiO2 seed layers are not yet understood clearly. Herein, based on the results of X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM), and analytical scanning/transmission electron microscopy (S/TEM) with semi-quantitative elemental mapping using energy dispersive X-ray (EDX) spectrum imaging, the post-annealing crystallization trend of r.f. magnetron sputter-deposited amorphous PZT films has been scrutinized as a function of TiO2 seed layer thickness. Upon annealing, PZT films on thin TiO2 layers (similar to 20-100 nm) partially crystallize into perovskite PZT via a transient pyrochlore/fluorite phase. However, no perovskite phase forms on thicker (similar to 550 nm) TiO2 layer. Thickness of underlying TiO2 seed layer strongly influences the crystallization, phase formation, texture, and surface morphology of the PZT films. During crystallization, Pb diffuses away from the PZT film to form solid solution with TiO2 seed layer. Perovskite PZT phase transformation requires a minimum Pb-concentration within the transient pyrochlore/fluorite phase. During the growth of perovskite grains, Zr gets segregated, resulting in Zr-concentration build-up within the surrounding disordered fcc fluorite phase.