Sol–Gel Synthesis and Characterization of Na 0.5 Bi 0.5 TiO 3 – NaTaO 3 Thin Films

Thin films with the composition 70 mol% Na 0.5 Bi 0.5 TiO 3  + 30 mol% NaTaO 3 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 / SiO 2 / TiO 2 / 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.