Combination of Solid-State and Electrochemical Impedance Spectroscopy To Explore Effects of Porosity in Sol–Gel-Derived BaTiO₃ Thin Films

BaTiO₃ thin films were deposited onto polycrystalline Pt using a dip-coating technique, with annealing temperatures of 750–900 °C. To avoid film imperfections such as cracking or pinholes, key conditions, including aging periods, water content, and stirring speeds, were refined to produce a pinhole-free, uniform film with some porosity. Whereas those coated a single time short circuited during electrical characterization, this could be avoided in films produced by multiple coating cycles. The effective permittivity of a 600 nm BaTiO₃ film was measured at 290 by fitting solid-state impedance data in the frequency range of 100 Hz to 1 MHz. Electrochemical impedance with an aqueous electrolyte allowed evaluation of the porosity, which remained fairly constant between 1 and 5 coating cycles. Using this method, it was possible to estimate the effective permittivity of the BaTiO₃ itself as 374 and hence to evaluate the increase in the effective permittivity that could be achieved by minimizing porosity.