Abstract
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.
Highlights
Titanate perovskites such as lead zirconate titanate (PbZrxTi1−xO3), strontium titanate (SrTiO3), and barium titanate (BaTiO3) are workhorse electroceramic materials
The effective permittivity of the BaTiO3 films of 290 that was derived from the solid-state impedance is significantly higher than that of air, and so it is reasonable to assume that the pores in the films contribute a negligible amount to the measured capacitance
The capacitance of the BaTiO3 films measured by electrochemical impedance spectroscopy, of ∼8 μF cm−2, shows a mixture of Pt double-layer capacitance due to electrolyte ingress through the pores and capacitance due to the BaTiO3 film
Summary
Titanate perovskites such as lead zirconate titanate (PbZrxTi1−xO3), strontium titanate (SrTiO3), and barium titanate (BaTiO3) are workhorse electroceramic materials. With these longer aging periods, the films developed small pores that could be observed under the microscope (distinct from the large pinholes described above that are visible to the naked eye), and increased in overall density (SI, Figure S2) This is consistent with an increase in sol viscosity.[37] On day 9, the sol had started to gel, and coatings produced from were not smooth or well adhered. Multiple sol−gel coating cycles have previously been reported to fill in the pores in BaTiO3 films and allow the solid-state impedance to be measured.[11] Figure 4 indicates that some porosity is present even in the films that have been coated multiple times. Be due to increasing thickness of the films and increasing tortuosity of the pores, resulting in a lower tendency for the evaporated gold, or other contact material, to penetrate to the substrate surface
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