Hetero-epitaxial growth and large piezoelectric effects in (0 0 1) and (1 1 1) oriented PbTiO₃-LaNiO₃ multilayers

Hetero-epitaxial thin films were obtained in PbTiO₃/LaNiO₃ thin films by using laser ablation for sequential deposition of each thin film. Structural variations were built to characterize the differences in local ferroelectric properties. For this study, 50 nm-thick-PTO thin films with (0 0 1) and (1 1 1) orientations were investigated. Piezoresponse force microscopy (PFM) was used to investigate the local ferroelectricity in the thin films. High piezoelectric responses were obtained in the thin films, with values of approximately 75 and 83 pm V^-1 in the (0 0 1) and (1 1 1)-oriented thin films, respectively. It is notable that remarkable piezoelectric properties were obtained in the (1 1 1)-oriented thin films. The (1 1 1)-oriented thin films have the potential to be used as multi-bit memory because of the reduction of degradation in ferroelectricity and various directional piezoelectricity. We compared the functionalities of the (0 0 1)- and (1 1 1)-oriented thin films and obtained different performances in the thin films.