Zirconium doped TiO2 thin films deposited by chemical spray pyrolysis

Abstract

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 TiO2 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 20at%. The Zr-doped TiO2 thin films were uniform and homogeneous showing much smaller grains than the undoped TiO2 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 6.4at% for the thin film deposited from the 20at% solution. According to AFM studies, Zr doping decreased the root mean square roughness of TiO2 film from 5.9 to 1.1nm. An XRD study of samples with the highest Zr amount showed the ZrTiO4 phase started forming after annealing at 800°C. The optical band gap for TiO2 decreased from 3.3eV to 3.0eV after annealing at 800°C but for the TiO2:Zr(20) film it remained at 3.4eV. 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.