The scientific motivation of this project proposal is to engineer complex oxide thin films based on bismuth ferrite (BiFeO3) by implementing new approaches of inducing strain for enhancing functional properties or even opening new ones.

       The aim of using strain engineering approach is to reveal the changes in optical properties as well as in the electrical ones for enhancing the efficiency of these materials in energy generation applications such as photocatalytic water splitting one. Different from the conventional epitaxial misfit homogenous strain induced in ferroelectric or multiferroic thin films, in this proposal strain gradients will be induced into the film’s thickness by growing compositionally graded thin films (e.g. Y-BFO thin films with Y-concentration varying with thickness) where the evolution of the lattice parameter with composition variation will impose a “chemical pressure” as driving force of the strain gradient.

       The other method is the orientation-driven strain control through substrates with different crystallographic orientation, as it has been already demonstrated for PbTiZrO3 materials, because there is the possibility of applying biaxial strain along other crystallographic planes than the “classical” (00l) and to engineer complex ferroelectric domain geometries Within this proposal, new strain engineering methods will be used on materials with different crystalline structures: Y-doped BiFeO3 is having a perovskite ABO3-type structure while the newly discovered KBiFe2O5 is having an A2B2O5 brownmillerite- type structure.

       The materials have been chosen on one hand due to narrow band gap values (1.97-2.35 eV for Y-BFO and 1.6 eV for KBiFe2O5), which are useful features in photocatalytic behavior, and on the other hand to confirm the efficiency of the induced strain pathways for different crystalline structure. The obtained thin films will be designed mainly having in mind the enhancement of their photoelectrochemical water splitting activity.