This study examines the volatilization of alkali elements on the surfaces of ceramic targets and in the deposited films during the deposition of potassium sodium niobate (KNN) thin films using a ceramic target with the nominal composition K0.55Na0.55NbO3 via a RF magnetron sputtering process. Under a 100 W RF power condition, significant volatilization of alkali elements occurred on the surface of the ceramic target, resulting in the inevitable formation of a Nb-rich secondary phase in the thin films. However, perovskite-phase KNN thin films with excellent reproducibility and without secondary phases were obtained under 50 W RF power and a substrate temperature of 600 °C. When the RF power was reduced to 20 W or the substrate temperature was lowered to 500 °C under 50 W RF power, no crystalline thin films could be obtained. Additionally, when the substrate temperature was raised to 700 °C under 50 W RF power, the niobium-rich secondary phase appeared in the thin films due to the volatilization of alkali elements. The conditions of 50 W RF power and a substrate temperature of 600 °C were found to be optimal for depositing perovskite-phase KNN thin films. However, complete suppression of potassium volatilization from the thin films was not achievable. Consequently, the resulting films had a sodium-rich composition compared to K0.5Na0.5NbO3 and exhibited lower dielectric constants along with relaxor ferroelectric characteristics. This study highlights the importance of monitoring the compositional changes in ceramic targets during the RF sputtering process to ensure high reproducibility in KNN thin film fabrication.

The grain growth behavior in the (1-x)K0.5Na0.5NbO3-xCaZrO3 (KNNCZ-x) system is studied as a function of the amount of CZ and grain shape. The (1-x)K0.5Na0.5NbO3-xCaZrO3 (KNNCZ-x) powders are synthesized using a conventional solid-state reaction method. A single orthorhombic phase is observed at x = 0 – 0.03. However, rhombohedral and orthorhombic phases are observed at x = 0.05. The grain growth behavior changes from abnormal grain growth to the suppression of grain growth as the amount of CaZrO3 (CZ) increases. With increasing CZ content, grains become more faceted, and the step-free energy increases. Therefore, the critical growth driving force increases. The grain size distribution broadens with increasing sintering time in KNNCZ-0.05. As a result, some large grains with a driving force larger than the critical driving force for growth exhibit abnormal grain growth behavior during sintering. Therefore, CZ changes the grain growth behavior and microstructure of KNN. Grain growth at the faceted interface of the KNNCZ system occurs via two-dimensional nucleation and growth.