Growth, microstructure, energy-storage and dielectric performances of chemical-solution NBT-based thin films: Effect of sodium nonstoichimometry

Na0.5+δBi0.5(Ti0.96W0.01Ni0.03)O3 thin films with various Na contents (abbreviated as Na.5+δBTWN, δ = − 3.0, − 1.5, 0, 1.5%) were fabricated on ITO/glass substrates using a chemical-solution process. The effects of Na nonstoichiometry on the microstructure, insulating, ferroelectric and dielectric performances are investigated. The pure perovskite phase can be obtained in Na0.5BTWN and Na0.515BTWN, while for Na0.470BTWN or Na0.485BTWN, the main composition contains secondary phase of TiO2. The grain size increases from 30 nm at δ = − 3.0% to 55 nm at δ = 0%, then decreases to 52 nm with δ = 1.5%. The leakage current of Na0.485BTWN sample is reduced dramatically in comparison with Na0.5+δBTWN (δ = − 3.0, 0, 1.5%). The big recoverable energy-storage density of 63.1 J/cm2 and high energy-storage efficiency of 55.0% can be obtained for Na0.485BTWN due to the improved electric break-down strength and large difference value between the remanent polarization and maximum polarization. Enhanced dielectricity is achieved in Na0.485BTWN with a high tunability of 36.0% and a figure of merit of 4.0 at 450 kV/cm and 500 kHz. These results demonstrated that the crystallization, micrographs and energy storage and dielectric properties of Na0.5Bi0.5TiO3 are highly sensitive to low levels of Na-site nonstoichiometry.