| As one promising lead-free piezoelectric materials, KNN-based thin films have received intensive attention to replace the currently market-dominating PZT-based thin films, with the concern of lead toxicity. Although high piezoelectric properties have been reported in KNN-based bulk ceramics, excellent piezoelectric properties have yet been obtained in KNN-based thin films. It is challenging to control the stoichiometry in KNN-based thin films, due to the serious alkali compositional loss. Moreover, the substrate stress also changes the film's crystalline structure and shifts the phase coexistence compositions. In this work, KNN-based thin films are prepared from chemical solutions, and the volatile compositional loss is suppressed by introducing appropriate combinational chemical agents. High-performance KNN-based piezoelectric films could be obtained by realizing rhombohedral-tetragonal coexistence. The effect of substrate-induced stress on film's phase coexistence compositions is investigated. Further improved piezoelectric properties are demonstrated in the (100)-oriented KNN-based films under reduced stress, exhibiting great potential for future applications. |
