Strain and Composition tuning in PbxSr1-xTiO3 thin films

Highly responsive, smaller and lighter ferro-piezoelectric materials have a great potential for piezoelectric applications, such as in the field of vibrational energy harvesting. It is thus particularly challenging to maintain good piezoelectric properties while reducing the physical dimensions of ferroelectric nano-objects. Furthermore, ferroelectric materials in thin films form appear today very promising in electronics so that intensive research is focused on the optimization of thin films growth and processing to achieve good piezoelectric response.In the present work, we have investigated the combined influence of epitaxial strain and compositional variation on the crystallographic structure, ferroelectric domain configuration and piezoelectric properties of PbxSr1-xTiO3 thin films and nanostructures epitaxially grown by Pulsed Laser Deposition on SrRuO3-buffered (110)-DyScO3 substrates. Theoretical predictions on the PbTiO3-SrTiO3 solid solution show an interesting phase transition as a function of composition when the films are grown under strain on single-crystal (110)-oriented DyScO3 substrates[1]. This phase transition was experimentally confirmed in films grown directly on the DyScO3 substrates by Molecular Beam Epitaxy using X-ray diffraction. Phase boundaries between different crystal phases are expected to show enhanced piezoelectric properties, similar to the well-known piezoelectric PZT. In the present work, we have thus investigated the effect of cation substitution (Pb2+ by Sr2+) on the ferroelectric phase and piezoelectric properties of PbxSr1-xTiO3 thin films. A series of thin films with various compositions of PbxSr1−xTiO3 have been grown by Pulsed Laser Deposition on SrRuO3-buffered (110)-DyScO3 atomically flat surfaces. This PbTiO3-DyScO3 film-substrate materials combination allows us to grow high quality epitaxial films thanks to the perfect lattice match at the growth temperature. The films thickness has been varied between 5 and 100 nm to change the strain state and valuable information about the films structure and ferroelectric states have been extracted from X-ray diffraction (XRD) measurements, in particular in grazing incidence using synchrotron radiation. The films domain structure and local piezoelectric response have then been studied by piezo-AFM as a function of their chemical composition and thickness