Stefano Boldrini: responsabile dell’unità CNR
Durata: 24 mesi. 28/09/2023 – 27/09/2025
Abstract: The proposal is focused on all-d-metal Heusler compounds, without critical raw materials (CRMs) and toxic elements, showing multifunctional properties ranging from thermoelectric conversion of waste heat to spintronics.
The challenge is to establish a link between the atomistic modelling of the electronic structure and the measured transport and magneto-electric properties of samples processed with scalable techniques.
The first objective is to understand the role of structural defects and magnetic disordering on the deviation of half-metallic behaviour from the Slater-Pauling rule, based on valence electron count. Ab-initio calculations will compute the relative stability of defective and non-defective structures in different Heusler compounds, establishing a guideline for the experimental verification of the interrelation between defects and properties through the combination of NMR experiments, transport and magneto-electric characterization of samples processed by different routes.
The second objective is to improve the efficiency of thermoelectric conversion in Heusler alloys, maximizing the figure of merit
ZT=(S^2*T)/(r*k)
(S, T, r, k are Seebeck coefficient, absolute temperature, electrical resistivity and thermal conductivity,
respectively) through doping to optimize S^2/r and decoupling electron/phonon scattering to minimize k. Increase of phonon scattering without affecting electrical conductivity can be targeted using scalable non-equilibrium processing routes to increase grain boundaries density.
The third objective is to control structural and microstructural features through compound design and process engineering, by comparing bulk samples and thin films, in order to maximize specific properties.
The proposers plan to achieve the goals offering multidisciplinary competences that cover ab-initio computation, metallurgical processing, thin film deposition, characterization of structural, microstructural, transport and magneto-electric properties.
The new proposed materials can spread across different fields of application, due to their versatility, availability and reduced environmental impact. In addition, all-d-metal Heusler alloys are expected to have improved mechanical properties, allowing the production of more robust and reliable devices.
From the thermoelectric point of view, the materials investigated can fill the gap in the medium-high temperature range (400-900 K) due to their thermal stability and ease of processing, reducing the payback time of investments for waste heat recovery applications.
In view of spintronic applications, new half-metallic Heusler alloys in the form of thin films will be grown and investigated. These materials can represent a breakthrough in modern computer technology thanks to the control of electronic structure and magnetic properties, leading to giant magnetoresistance and high Curie temperature, guaranteeing half-metallic behaviour and high spin polarization at room temperature.
