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

Abstract Na 0.5+δ Bi 0.5 (Ti 0.96 W 0.01 Ni 0.03 )O 3 thin films with various Na contents (abbreviated as Na .5+δ BTWN, 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 Na 0.5 BTWN and Na 0.515 BTWN, while for Na 0.470 BTWN or Na 0.485 BTWN, the main composition contains secondary phase of TiO 2 . 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 Na 0.485 BTWN sample is reduced dramatically in comparison with Na 0.5+δ BTWN (δ = − 3.0, 0, 1.5%). The big recoverable energy–storage density of 63.1 J/cm 2 and high energy–storage efficiency of 55.0% can be obtained for Na 0.485 BTWN due to the improved electric break–down strength and large difference value between the remanent polarization and maximum polarization. Enhanced dielectricity is achieved in Na 0.485 BTWN 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 Na 0.5 Bi 0.5 TiO 3 are highly sensitive to low levels of Na–site nonstoichiometry.