Diffuse phase transition in Nb-doped BaTi₂O₅ thin films

BaNb_xTi_2–xO₅ (x = 0, 0.002, 0.004, 0.006, 0.008, 0.01) thin films were deposited on the Pt(111)/Ti/SiO₂/Si substrates using the sol–gel method. The effect of Nb⁵⁺ substitution on the electric properties of BaNb_xTi_2–xO₅ films was investigated. Diffuse phase transition was observed in all the thin films. The relationship between the dielectric constant and temperature of these films showed a wide platform and no frequency dependence. For the film with x = 0.006, an abnormally broadened dielectric platform was obtained in the temperature range of 200–400 °C, and its value fluctuated in the range of 350 ± 10. The research showed that Nb-doped and thermal stress contributed greatly to this abnormally broadened platform of ε(T) curve. The substituting Nb⁵⁺ in BaTi₂O₅ thin films caused small microscopic composition fluctuation, which enhanced the degree of diffusion phase transition of the films. And the thermal stress on the films caused inhomogeneous polarization of the surface and center of the films, resulting in a change in phase transition behavior. In addition, the BaNb_xTi_2–xO₅ thin films with high dielectric constant at high temperatures were successfully obtained, which were beneficial to the application of BaTi₂O₅ films under high temperature conditions.