Relaxation mechanism of interfacial lattice misfit between PZT and SRO in a thin-film actuator

Abstract

In thin-film actuators with PbZr_1−xTi_xO₃ (PZT)/SrRuO₃ (SRO)/Pt layered structures, the SRO buffer layer shows favorable effects such as improved electrical properties and reduced oxygen vacancies in the PZT film. However, when the PZT composition becomes near the morphotropic phase boundary for enhanced piezoelectric properties, the lattice misfit of approximately 3 % should be formed at the PZT/SRO interface. Consequently, a mechanism to relax this lattice misfit should be required. Here, we investigated the lattice misfit relaxation mechanism using (Scanning) Transmission Electron Microscopy [(S)TEM]. We found that the lattice misfit was relaxed not only by the edge-type misfit dislocations at the interface but also by the twins in the SRO buffer layer. The twins in the SRO film form prior to the PZT film deposition, possibly due to the surface condition of the Pt substrate. These findings suggest that the Pt surface condition may affect the structure and properties of PZT/SRO/Pt.