Effect of Nb doping on the phase transition and optical properties of sol–gel TiO2 thin films

Abstract Various content Nb-doped TiO 2 thin films were prepared by sol–gel process. XRD analysis shows that the existence of crystalline TiO 2 in anatase and rutile form depends on the Nb content in the examined samples. It is observed that Nb promotes the anatase to rutile phase transition but has a depression effect on the anatase grain growth. It is found that incorporation of about 4 at.% of Nb completely transforms anatase TiO 2 to the rutile form at a calcination temperature as high as 900 °C. The mechanism is proposed. Optical analyses show that the films have an average of 60% transmission in visible region. The energy gap values using Tauc's formula have also been estimated. The band gap of rutile Ti 1− x Nb x O 2 solid solutions increases with increasing x .