Lead-free 0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 thin films with enhanced electric properties fabricated from optimized sol-gel systems

0.5Ba(Ti0.8Zr0.2)O3-0.5(Ba0.7Ca0.3)TiO3 (0.5BZT-0.5BCT), one of the most promising lead-free piezoelectric materials invented in recent years, has not been optimized for its thin film to show best electric performance. In this work, 0.5BZT-0.5BCT thin films were fabricated via a sol-gel technique, and the effects of solvent and additive on the microstructure, morphology and dielectric, ferroelectric, and piezoelectric properties were studied. Results showed that the 2-methoxyethanol (2-MOE) solvent resulted in 0.5BZT-0.5BCT thin films with much improved microstructure and morphology in comparison with thin film from absolute ethanol solvent. Furthermore, the film becomes even denser, smoother, and more homogeneous after the monomer ethylene glycol (EG) or polyethylene glycol of 400 molecular weights (PEG400) were added into the precursor with 2-MOE as solvent. Especially, addition of PEG400 into the solvent will result in the best thin film with both less macro and micro defects and high electric performance. The 0.5BZT-0.5BCT film from 2-MOE solvent with PEG400 additive shows a high dielectric constant ε up to 1756, dielectric tunability about 44%, Pr around 17.2 μC/cm2, and Ec about 39.0 kV/cm.