Ferroelectric and dielectric properties of Ca2+-doped and Ca2+-Ti4+ co-doped K0.5Na0.5NbO3 thin films
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Chemical solution deposition (CSD) of K0.5Na0.5NbO3 (KNN) thin films on silicon-based substrates is an interesting technology for fabrication of lead-free ferroelectric thin films. Here, we report on improved ferroelectric and dielectric properties of KNN thin films prepared by CSD through Ca2+-doping and Ca2+-Ti4+ (CaTiO3) co-doping. Undoped KNN, 0.5 mol% Ca2+-doped and 0.5 mol% CaTiO3-doped KNN films were deposited on platinized silicon substrates by aqueous CSD. X-ray diffraction of the films as well as powders, prepared from the precursor solutions, confirmed that the three KNN materials were single phase solid solutions. A smaller grain size was observed for the doped relative to undoped KNN films. Investigation of the ferroelectric properties of the thin films demonstrated that Ca2+- and CaTiO3-doping promotes ferroelectric switching, with a low leakage current and remnant polarization of 6.37±0.47 and 7.40±0.09 μC cm-2 of the Ca2+- and CaTiO3-doped films, respectively. The dielectric constants of the films were among the highest measured for KNN films from CSD and span from 1800 to 3200 at 1 kHz.