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

BaTiO 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 BaTiO 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 BaTiO itself as 374 and hence to evaluate the increase in the effective permittivity that could be achieved by minimizing porosity.