Epitaxial strain stabilization of a ferroelectric phase in PbZrO ₃ thin films

PbZrO₃/SrRuO₃/SrTiO₃ (100) epitaxial heterostructures with different thickness of the PbZrO₃ (PZO) layer (d_PZO∼5-160 nm) were fabricated by pulsed laser deposition. The ultrathin PZO films (d_PZO≤10 nm) were found to possess a rhombohedral structure. On increasing the PZO film thickness, a bulk like orthorhombic phase started forming in the film with d_PZO∼22 nm and became abundant in the thicker films. Nanobeam electron diffraction and room-temperature micro-Raman measurements revealed that the stabilization of the rhombohedral phase of PZO could be attributed to the epitaxial strain accommodated by the heterostructures. Room-temperature polarization vs electric field measurements performed on different samples showed characteristic double hysteresis loops of antiferroelectric materials accompanied by a small remnant polarization for the thick PZO films (d_PZO50 nm). The remnant polarization increased by reducing the PZO layer thickness, and a ferroelectric like hysteresis loop was observed for the sample with d_PZO∼22 nm. Local ferroelectric properties measured by piezoresponse force microscopy also exhibited a similar thickness-dependent antiferroelectric-ferroelectric transition. Room-temperature electrical properties observed in the PZO thin films in correlation to their structural characteristics suggested that a ferroelectric rhombohedral phase could be stabilized in thin epitaxial PZO films experiencing large interfacial compressive stress.