PMN-PT (70/30) thin films were deposited by sputtering on silicon substrate covered with different bottom electrodes: TiOx/Pt and LaNiO3 (LNO). The bilayers TiOx/Pt are deposited by sputtering and the LNO layer by sol–gel. Whatever the bottom electrodes the perovskite phase appears at 400 °C; the existence of a buffer layer (Pb2Nb2O7) between the PMN-PT film and the bottom electrode could explain the perovskite formation of the PMN-PT films at this low temperature. We have studied the interfacial layer by transmission electron microscopy (TEM), high-resolution X-ray diffraction (HR XRD), and the measurement of the dielectric properties of the structures. The dielectric measurements are in accordance with the TEM and HR XRD analysis: the existence of a Pb2Nb2O7 interfacial layer which can play the role of a buffer layer as well on LNO as TiOx/Pt.