Zirconium doped TiO ₂ thin films deposited by chemical spray pyrolysis

Chemical spray pyrolysis (CSP) is a flexible deposition technique that allows for mixing of the precursor solutions in different proportions suitable for doping thin films. The CSP method was used to dope TiO ₂ thin films with Zr by adding zirconium(IV) acetylacetonate into a solution of titanium(IV) isopropoxide in ethanol stabilized by acetylacetone at [Zr]/[Ti] of 0, 5, 10 and 20 at%. The Zr-doped TiO ₂ thin films were uniform and homogeneous showing much smaller grains than the undoped TiO ₂ films. Zr stabilized the anatase phase to temperatures above 800 °C depending on Zr concentration in the spray solution. The concentration of Zr determined by XPS was 6.4 at% for the thin film deposited from the 20 at% solution. According to AFM studies, Zr doping decreased the root mean square roughness of TiO ₂ film from 5.9 to 1.1 nm. An XRD study of samples with the highest Zr amount showed the ZrTiO ₄ phase started forming after annealing at 800 °C. The optical band gap for TiO ₂ decreased from 3.3 eV to 3.0 eV after annealing at 800 °C but for the TiO ₂ :Zr(20) film it remained at 3.4 eV. The dielectric constant increased by more than four times with Zr-doping and this was associated with the change in the bond formations caused by substitution of Ti by Zr in the lattice.