Niobia-stabilised anatase TiO2 highly porous mesostructured thin films

The thermal stability of anatase TiO2 mesoporous thin films has been considerably increased up to 800 °C by substituting a fraction of Ti cations by Nb. Mesoporous mixed oxide films Ti1-xNbxO2, with x = Nb/(Nb + Ti) ranging from 0 to 1, and homogeneous crystalline walls have been successfully prepared from chloride precursors and non-ionic block copolymer templates. They all exhibit a uniaxially distorted Im3m bcc mesostructure with the a lattice parameter ranging from 14 to 19 nm. Films have been characterised by simultaneous in situ SAXS and WAXS investigations during thermal treatment. Transmission electron microscopy and UV-visible ellipsometry were used to confirm the structure, the porosity and the good optical quality. A high porosity of 40% (pore size estimated at 7 nm) was maintained for the 10% Nb-doped films above the temperature of crystallisation and a bandgap of 3.40 eV has been measured after annealing at 500 °C.