Effect of Na/K excess on the electrical properties of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 thin films prepared by sol–gel processing

(Na0.85K0.15)0.5Bi0.5TiO3 (NKBT) thin films derived from different amounts of Na/K excess content were fabricated via an aqueous sol–gel method on a Pt(111)/Ti/SiO2/Si substrate, and the effect of Na/K excess content on the microstructure and electrical properties of the NKBT thin films was investigated. A second phase appears when Na/K excess content is below 20 mol%. Appropriated Na/K excess can enhance the polarization and dielectric properties due to compensation of Na/K loss that occurred during heat treatment. The 20 mol% excess derived NKBT thin film exhibits the best ferroelectric and dielectric properties with a remnant polarization (Pr) of 13.6 μC/cm2, and a coercive field (Ec) of 104.8 KV/cm, together with a dielectric constant of 406 and a dissipation factor of 0.064. Similar to the dielectric response change with Na/K excess content, the decreasing concentration of charged defects is the main reason resulting in the increase of the piezoelectric property. The film with a 20 mol% excess content exhibited an effective d33⁎ of about 56 pm/V. Also, the NKBT with a 20 mol% excess content exhibits the lowest current density of 5.6 × 10− 5 A/cm2 at 10 V.