Effect of deposition temperature on structural, mechanical, optical and dielectric properties of radio frequency sputtered nanocrystalline (KxNa1 − x)NbO3 thin films

We report a systematic investigation on the effects of substrate temperatures and O2percentage on crystallinity, microstructure, optical, mechanical and dielectric properties of (KxNa1 − x)NbO3 thin films deposited at different substrate temperatures by radio frequency magnetron sputtering. It is observed from X-ray diffraction patterns that the as-made films at room temperature and 200 °C exhibit amorphous structures, while the films deposited at 400 °C show significant crystallinity with K2Nb6O16 as a secondary phase. Interestingly, the films deposited at high substrate temperature exhibit improved optical, mechanical and dielectric properties and reveal higher refractive indices in the range of 2.0-2.16 at 600 nm. Nevertheless, the optical bandgap of the amorphous films is found to be larger than those obtained in crystalline films. Furthermore, the hardness (1.0-9.4 GPa) and elastic modulus (26.7-100.2 GPa) are strongly dependent on average grain size and deposition temperature. The dielectric properties of (KxNa1 − x)NbO3 films deposited at 400 °C showed dielectric properties (dielectric constant (εr) = 229 and tanδ = 0.009 measured at 1 MHz) and the observed optical, mechanical and dielectric properties exhibit profound dependence on deposition temperature, O2 percentage, crystallinity, microstructure and packing densities.