Composition dependence of optical constants in ferroelectric Ba(Ti1 − x,Nix)O3 thin films by optical transmittance technique

Ba(Ti1 − x,Nix)O3 ferroelectric thin films with perovskite structure are prepared on fused quartz substrates by a sol–gel process. Optical transmittance measurements indicate that Ni-doping has an obvious effect on the energy band structure of BaTiO3. It has been found that the refractive index n, extinction coefficient k, and band gap energy Eg of the films are functions of the film composition. The Eg of Ba(Ti1 − x,Nix)O3 decreases approximately linearly as the Ni content increases, which is attributed to the decline of conduction band energy level with increasing the Ni content. On the other hand, n and k both increase linearly with increasing the Ni content because of the increase of packing density. These results indicate that thin films might have potential applications in BaTiO3-based thin-film optical devices.