Superior electromechanical performance over PZT, in lead zinc niobate (PZN)-lead zirconium titanate (PZT) thin films

Strongly oriented thin films of lead zinc niobate (PZN)-lead zirconium titanate (PZT) with (La,Sr)CoO3 lower electrodes were grown on MgO (001) substrates by pulsed laser deposition. The films were perovskite-dominated with strong in-plane and out-of-plane orientations. Room-temperature functional characterisation indicated that the films were ferroelectric, with dielectric constant ∝550 and loss tangent ∝0.08 at 1 kHz. The crystallographic strain, as a function of applied dc field, was monitored by in situ X-ray diffraction. The maximum electric-field-induced crystallographic strain (∝0.22%) was comparable to that observed in bulk, but at significantly greater field (∝150 kVcm-1). The effective d33 value obtained from the crystallographic strain data was around 150 pm V-1, which is high for ferroelectric thin films 400 nm in thickness. The local polarisation-switching properties of the films were investigated using a piezo-response atomic force microscope. Domain maps for a 5 x 5 μm2 region of material were recorded as a function of dc bias, and confirmed the ferroelectric switching behaviour. (orig.)