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RÉFÉRENCE : MRT-2018-023
Type : Doctorant
Type de contrat : CDD
Durée : 12 months
Lieu de travail : Belvaux

CONTEXTE

Thesis title
Scale law on energy efficiency of electrocaloric ceramics for future cooling applications

DESCRIPTION

Caloric materials are considered as one of the most promising fields of solid state research when it comes to revolutionize cooling technologies. This challenge is important as we spend in Europe more than 15% of our energy to refrigerate food or cool down our houses. Therefore any new technology must be energy efficient. And it turns out that Electrocaloric (EC) materials – temperature change triggered by electric field – are particularly well suited to high efficiency.
Consequently, the objective of this PhD is to identify the material parameters inducing high efficiency in EC systems.

This objective raises three scientific questions :

1) What are the EC materials with the largest variation of temperature ?
2) What are the EC materials with the highest material efficiency ?
3) How heat exchange occurs in EC materials ?

90% of the literature is focused on the first question, which means that the best materials have already been identified (relaxors and antiferroelectrics). On the contrary, the questions addressing energy efficiency and heat exchange in EC materials have been largely overlooked, though they are equally important when it comes to EC systems. We will focus on these two last questions in this study.

Our approach consists in choosing three excellent EC materials of different sizes, shapes and architectures (bulk, thick and thin films, multilayer capacitor structure). We will study their material efficiency, which is the ratio of electrical work over the heat generated by the EC effect. We will also study how to extract heat from these EC materials either by conduction or convection. We will then combine our findings to identify the materials parameters enabling high efficiency in future EC systems.

Methodology

On the one hand, we will produce sol gel precursors of three identified materials and will deposit them on different substrates. On the other hand, we will collect (or have already collected) bulk and Multi Layer Capacitors samples of the selected materials. There is no requirements for the PhD candidate to have specific knowledge on this aspect as we have it here at LIST.
We will perform direct characterization of the EC effect mainly through IR camera and also modified Differential Scanning Calorimetry. IR camera is our key characterization means and will have to be mastered by the PhD, keeping in mind that we already started developing this tool at LIST regarding the EC effect.
Then, we will study the material efficiency of the samples prepared and collected beforehand. Materials efficiency is the ratio of the electrical work needed to trigger the EC effect over the heat generated by this EC effect.
We will also study the heat exchange of these EC materials with solids (conduction) and fluids (convection) with specific set-ups. This task goes towards EC systems for which we need to identify the best ways to extract heat from EC materials.

PROFIL

Education

• Master 2 in Material Science or Physics

Competencies

• The candidate will have to exhibit a strong taste for experimental physics
• Shall be a team player
• Some knowledge on thermodynamics and/or heat exchange would be an asset

Language

• Fluent in English (spoken and written) is mandatory