On the nature of niobium substitution in niobium doped titania thin films by AACVD and its impact on electrical and optical properties†
Niobium doped TiO2 thin films were deposited on silica coated glass substrate using aerosol assisted chemical vapour deposition (AACVD) from hexane solution, at 500 °C. The as-deposited films appeared blue, were transparent in the visible, were reflective in the IR region at around 30% and were electrically conductive (n = 1.23 × 1019 cm−3, μ = 18.9 cm2 V−1 s−1, sheet resistance = 120 Ω □−1). The structure of the films was investigated using XRD, Raman spectroscopy, XPS and X-ray absorption spectroscopy (XAS). No visible phase segregation was found by XRD nor by Raman, though analysis of the Nb K-edge using XANES and EXAFS revealed the presence of niobium both incorporated into the titanium dioxide lattice as well as present in the form of Nb2O5. The high resolution TEM imaging showed sub 4 nm Nb2O5 crystals within the lattice. This work questions the solubility limit of niobium in the TiO2 lattice and suggests previous literature on Nb-doped TiO2 may have overestimated the degree of niobium substitution.
- This article is part of the themed collections: Celebrating the 2016 RSC Prize and Award Winners and Highlighting materials research in the UK for energy and sustainability