Tailoring Metastable phases in nickelates: toward neuromorphic functionalities – TaMe

Topotactic processes are promising synthesis routes for creating new phases of oxides with ordered networks of oxygen vacancies. The main objective of the TaMe project is to control such transitions in rare-earth nickelates, RNiO3 (R being a rare-earth), by interfacing them with a ferroelectric material. The variations of strain and charge transfer at the interfaces, induced by an applied electric field will permit the formation and/or coexistence of several phases with varying conductive or capacitance properties, which will be later used in neuromorphic devices.
To reach our goal, we will first predict, via a computational approach based on ab initio calculations, the main factors (choice of the ferroelectric (FE) material and of the RNiO3 chemical composition to modulate the strain and oxidation degrees) to stabilize/discover novel RNiO3-x phases which are metastable and exhibit distinct electronic and polar states. We will then use Pulsed Laser Deposition (PLD) techniques and topotactic processes to fabricate high-quality thin films either capped with FE layers or/and grown on a FE substrate. The quality of our films will be controlled using standard characterization techniques giving access to structural and chemical information, as well as magnetic and transport properties. Finally, we will combine advanced characterization techniques (transmission electron microscopy and synchrotron techniques) and numerical calculations to measure and understand the electronic and structural properties of the nickelate thin films and their interfaces. Controlling the transition or the ratio between several metastable phases coexisting in the same sample will allow the generation of multiple intermediary states, useful to design memresistive or memcapacitance devices with neuronal and synaptic functions.