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Thin films with the composition 70 mol% Na0.5Bi0.5TiO3 + 30 mol% NaTaO3 were prepared by sol–gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low‐ (kHz–MHz) and microwave‐frequency (15 GHz) ranges were investigated. In the low‐frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature‐stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between −25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO2/TiO2/Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.

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This work examines the synthesis and characterization of crack‐free, β‐Bi2O3 thin films prepared on Pt/TiO2/SiO2/Si or corundum substrates using the sol‐gel method. We observed that the Bi‐based precursor has a pronounced influence on the β‐Bi2O3 phase formation. Well‐crystallized, single β‐Bi2O3 thin films were obtained from Bi‐2ethylhexanoate at a temperature of 400°C. In contrast, thin films deposited from Bi‐nitrate and Bi‐acetate resulted in non‐single Bi2O3 phase formation. TEOS was used for the stabilization of the β‐Bi2O3 phase. The phase composition of the thin films was characterized by means of X‐ray diffraction (XRD), whereas the morphology and thickness of the thin films were studied using scanning electron microscopy (SEM). The β‐Bi2O3 films' dielectric properties were characterized utilizing microwave‐frequency measurement techniques: (1) the split‐post dielectric resonator method (15 GHz) and (2) the planar capacitor configuration (1–5 GHz). The dielectric constant and dielectric loss measured at 15 GHz were 257 and 7.5 × 10−3, respectively.