Dielectric and Optical Characterization of RF Sputtered Ba₅Nb₄O₁₅–BaWO₄ Composite Films for Electronic and Smart Window Applications

Abstract

We demonstrate the deposition of Ba₅Nb₄O₁₅–BaWO₄ (BNO–BWO) composite thin films by radio frequency (RF) magnetron sputtering under different oxygen mixing percentages (OMP). Significantly, the x-ray diffractometer revealed the coexistence of both BNO hexagonal perovskite structure with BWO scheelite structure. The microstructures of the composite films reveal two types of grains: BNO exhibited small rod-shaped grains, whereas the BWO showed large hexagonal grains, and the chemical compositions of these grains are confirmed using energy dispersive spectroscopy analysis. The optical transmittance of the as-deposited films show the transmittance above 90% and after annealing they exhibit pale yellow color, and this response may be due to the electrochromic response of these films. The refractive index of the films decreases for the films deposited above 25% OMP, whereas the optical bandgap increases with an increase in OMP. The dielectric response of Ag/BNO–BWO Pt/Ti/SiO₂/Si thin film capacitors showed that the obtained dielectric properties are independent of measured frequency and temperature. The split-post dielectric resonator method was used to measure dielectric properties at discrete microwave frequencies (5, 10, and 15 GHz) and are in the range of ε _r  = 22.47–49.81 and tanδ = 0.0038–0.0010, for annealed films. The activation energies of the composite films obtained from the Arrhenius relation are in the range of 0.021–0.008 eV. BNO–BWO nanocomposite films find applications in integrated electronic devices, smart windows, and information display applications.