A comprehensive investigation of the structural properties of ferroelectric PbZr0.2Ti0.8O3 thin films grown by PLD

X-Ray diffraction investigations were made of high-quality epitaxial thin films of the ferroelectric material lead zirconate titanate, PbZr0.2Ti0.8O3 (PZT), grown by pulsed laser deposition (PLD). Layers from 7 to 200 nm in thickness were studied, deposited on a 30 nm SrRuO3 (SRO) electrode on a [001] oriented SrTiO3 (STO) substrate. The out-of-plane lattice parameters of the PZT films were measured by high-resolution X-ray diffraction using CuK alpha(1) radiation. A significant enhancement of the c lattice parameter with film thickness was observed, the maximum value of 4.25 angstrom reached in the 30-50 nm thick films. For film thicknesses greater than 100 nm, the c lattice parameter is relaxed, towards the bulk value of 4.13 angstrom at this composition. The in-plane lattice parameters were studied by Grazing incidence X-ray scattering (GIXS), using 15 keV synchrotron radiation at 116, Diamond. The a lattice parameter of domains with [001] oriented normal to the sample surface was effectively lattice matched to the SRO layer in the 7 nm ultra-thin film, but relaxed compared to the SRO in thicker films. The tetragonality of the [001] oriented domains decreases with increasing film thickness, approaching the bulk value of 1.05 in the thickest films. Evidence for the presence of [100] oriented a-domains was found in PZT films as thin as 30 nm, the proportion of which increased with increasing film thickness, suggesting they grow in order to relieve stresses that would prevent the epitaxial growth of thicker PZT films. The a-domains in the thicker films were found to be located nearer to the PZT/SRO interface than to the top surface of the PZT. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim