Seed layers of (TiO2)x(PbO)y for the growth Pb(Z,Ti)O3 (PZT) thin films have been studied as a function of thickness and composition. The seed layers have been deposited by reactive in-situ sputter deposition at 530°C from two metal targets in a dynamic sputtering mode. The compositional variation was achieved by varying the relative fluxes. The PZT process was run with a limited lead excess resulting in pyrochlore nucleation on bare Pt electrodes. When the electrode was covered with a dense seed layer, perovskite was obtained everywhere. Ti rich seed layers yielded (111)-textured PZT even for very thin seed layers. Pb rich seed layers nucleated as PbTiO3{100} and gave rise to (100)-textured PZT. In an intermediate zone, the major perovskite orientations (100), (110) and (111) have been found together with pyrochlore for a small seed layer thickness. In this zone, the seed layer nucleates in islands leaving bare Pt spots. The intermediate region is a transition region between (111) seeds and (100) seeds. The latter exhibit diverging critical sizes at a given critical flux ratio, leading to large nuclei and bare Pt. Small perovskite(111) seed grains in the 10 to 100 nm range are found at equal lead oxide and titania flux.