Crystalline phase and electrical properties of lead‐free piezoelectric KNN ‐based films with different orientations

Lead‐free piezoelectric 0.915K 0.5 Na 0.5 NbO 3 ‐0.075BaZrO 3 ‐0.01Bi 0.5 Na 0.5 TiO 3 ( KNN ‐ BZ ‐ BNT ) films were grown on Nb‐doped SrTiO 3 substrates with different orientations. The thin films show highly preferential orientations in accordance with the orientations of single crystalline substrates. The films all exhibit a weak contrast and remarkable homogeneity in the local static out‐of‐plane piezoresponse phase images, suggesting a strong self‐polarization. Combining with the analysis of XRD ‐ RSM , TEM and PFM , the crystalline phase of our samples was determined to be rhombohedral, which has the spontaneous polarization along [111] direction. Thus, the (100)‐oriented film demonstrates the most superior piezoelectric properties. Our detailed studies on structural and electrical properties of KNN ‐ BZ ‐ BNT films further clarify the structure‐property relationship and make a step closer to use this lead‐free material for many piezoelectric applications.