The influence of A-site rare-earth for barium substitution on the chemical structure and ferroelectric properties of BZT thin films

Rare-earth (RE) doped Ba(ZrTi)O-3 (BZT) thin films were prepared by rf-magnetron sputtering from a Ba(0.90)Ln(0.067)Zr(0.09)Ti(0.91)O(3) (Ln = La, Nd) target. The films were deposited at a substrate temperature of 600 degrees C in a high oxygen pressure atmosphere. X-ray diffraction (XRD) patterns of RE-BZT films revealed a < 001 > epitaxial crystal growth on Nb-doped SrTiO3, < 001 > and < 011 > growth on single-crystal Si, and a < 111 >-preferred orientation on Pt-coated Si substrates. Scanning electron microscopy (SEM) showed uniform growth of the films deposited, along with the presence of crystals of about half-micron size on the film's surface. Transmission electron microscopy (TEM) evidenced high crystalline films with thicknesses of about 100nm for 30min of sputtering. Electron-probe microanalysis (EPMA) corroborated the growth rate (3.0-3.5 nm/min) of films deposited on Pt-coated Si substrates. X-ray photoelectron spectroscopy (XPS), in depth profile mode, showed variations in photoelectron Ti 2p doublet positions at lower energies with spin-orbital distances characteristic of BaTiO3-based compounds. The XPS analysis revealed that lanthanide ions positioned onto the A-site of the BZT-perovskite structure increasing the MO6-octahedra distortion (M = Ti, Zr) and, thereby, modifying the Ti-O binding length. Polarization-electric field hysteresis loops on Ag/RE-doped BZT/Pt capacitor showed good ferroelectric behavior and higher remanent polarization values than corresponding non-doped system. (C) 2009 Elsevier Inc. All rights reserved.