Influence of the Template Layer on the Structure and Ferroelectric Properties of PbZr_0.52Ti_0.48O₃ Films

The microstructure of the PbZr_0.52Ti_0.48O₃ (PZT) films is known to influence the ferroelectric properties, but so far mainly the effect of the deposition conditions of the PZT has been investigated. To our knowledge, the influence of the underlying electrode layer and the mechanisms leading to changes in the PZT microstructure have not been explored. Using LaNiO₃ (LNO) as the bottom electrode material, we investigated the evolution of the PZT microstructure and ferroelectric properties for changing LNO pulsed-laser deposition conditions. The explored deposition conditions were the O₂ pressure, total pressure, and thickness of the electrode layer. Increasing both the O₂ pressure and the thickness of the electrode layer changes the growth of PZT from a smooth, dense film to a rough, columnar film. We explain the origin of the change in PZT microstructure as the increased roughness of the electrode layer in relaxing the misfit strain. The strain relaxation mechanism is evidenced by the increase in the crystal phase with bulk LNO unit cell dimensions in comparison to the crystal phase with substrate-clamped unit cell dimensions. We explain the change from a dense to a columnar microstructure as a result of the change in the growth mode from Frank-van der Merwe to Stranski-Krastanov. The ferroelectric properties of the columnar films are improved compared to those of the smooth, dense films. The ability to tune the ferroelectric properties with the microstructure is primarily relevant for ferroelectric applications such as actuators and systems for energy harvesting and storage.