Structure and properties of WO3-doped Pb0.97La0.03(Zr0.52Ti0.48)O3 ferroelectric thin films prepared by a sol-gel process

Abstract

Lanthanum-modified lead zirconate titanate Pb0.97La0.03(Zr0.52Ti0.48)O3 doped with xat.% WO3 (x=0, 0.2, 0.5, 1, and 2) (PLWZT) ferroelectric thin films have been deposited on Pt∕Ti∕SiO2∕Si substrates using a sol-gel spin-coating process. We have demonstrated that WO3 dopant plays a significant role on the structure and electrical properties of the PLWZT films. The x-ray-diffraction analysis shows that the PLWZT films undergo a dramatic tetragonal-to-cubic crystalline phase transformation with small amount of WO3 additives. Surface morphology (atomic force microscopy) analysis shows that the average grain size decreases with the increase of WO3 doping amount in the PLWZT films. The highest average grain size of 91nm has been observed for PLWZT (WO3:0.2at.%). It is also observed from x-ray photoelectron spectroscopy study that W varies its chemical state with the varying concentration of WO3 in the films. Moreover, the polycrystalline PLWZT thin films with a small amount of WO3 doping (0.2at.%) show a reduced electrical conductivity, improved dielectric constant (ε) (1675 at 1kHz) and decreased dielectric loss (D) (0.03 at 1kHz), and improved remnant polarization (Pr) value of 30μC∕cm2 along with significantly improved fatigue resistance (∼5% attenuated after 108 switching cycles) compared with the other PLWZT films. A defect chemistry mechanism indicating the reduction of oxygen vacancies by the substitution of W for Ti at different doping concentrations has been proposed to well explain the observed experimental results.