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 SrTiO3 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.