Preparation and Investigation of Sol–Gel TiO2-NiO Films: Structural, Optical and Electrochromic Properties

Abstract

TiO2 and TiO2-NiO films were successfully derived by a sol–gel dip coating technology. The impact of the thermal treatments (300–600 °C) on the structural, optical and electrochromic properties was investigated. X-ray diffraction (XRD) analysis showed that TiO2 films were polycrystalline and evolved in the anatase phase. The composite TiO2-NiO films, treated at annealing temperatures below 500 °C, contained anatase titania, a small inclusion of cubic NiO and an amorphous fraction. The formation of NiTiO3 was exposed after the highest annealing at 600 °C. The presence of Ti-O-Ni bonds was determined in the composite films by Fourier-transform infrared (FTIR) spectroscopy. The optical properties and the optical band gap of TiO2-NiO films were investigated and discussed. The transparency of the electrochromic TiO2-NiO films was 76.8 and 78.3% in the 380–700 nm spectral range after film thermal treatments at 300 and 500 °C. NiO incorporation led to the narrowing of the optical band gap. The electrochromic (EC) properties of the composite films were improved compared to TiO2 films. They had higher diffusion coefficients. Their color efficiencies are 37.6 (550 nm) and 52.2 cm2/C (600 nm).