Large piezoresponse of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 thin films prepared via water-based sol–gel method

(Na0.85K0.15)0.5Bi0.5TiO3 (abbreviated as NKBT) thin films were fabricated via an economical aqueous sol–gel method on Pt(1 1 1)/Ti/SiO2/Si substrates. Overdoping of volatile cations in the precursor solutions was necessary to achieve pure perovskite structure due to compensation of cations loss that occurred during heat treatment. Different annealing temperature was investigated to get the films with single perovskite phase detected by XRD patterns. Thin films of 250 nm thickness exhibited a dielectric constant and a loss tangent at 100 kHz of 519 and 0.058, respectively. A high effective piezoelectric coefficient (d33) of approximately 76 pm/V was obtained via PFM.