Description du sujet de thèse

Manipulating heat flows remains a challenge today. Though, this control is essential for better energy management of our daily devices. In particular, the development of thermal switches and thermal diodes would significantly improve the performance of solid-state refrigeration systems, the development of high-efficiency solar panels and the realization of high-performance thermoelectric devices [1]. However, current thermal switches and diodes are not efficient enough to fulfill this role.

As part of this project, the PhD student will explore a fundamentally new mechanism for designing efficient thermal switches and diodes. Indeed, recent experimental results have shown that (anti)ferroelectric oxides can be used to achieve dynamic control of heat flows [2]. Ferroelectric oxides organize themselves spontaneously into domains – separated by domain walls – where the positions of the atoms are slightly different [3]. These domain walls have a direct impact on the propagation of phonons that conduct heat. The greater the density of domains, and therefore of domain walls, the greater the number of collisions between phonons and domain walls and the lower the thermal conductivity. And it is precisely possible to control the density of domains by applying an electric voltage.

The objective of this PhD is to demonstrate the control of thermal conductivity, via an electric field, thanks to the control of domain walls in relaxor and antiferroelectric oxides. The student will synthesize different materials, shaped as ceramics or monocrystals, and will optimize their domain structure via different treatments (e.g. annealing). They will characterize their ferroelectric properties (polarization-electric field hysteresis curves, impedance spectroscopy) and study their response to an electric field. Finally, they will characterize their thermal properties, in particular via the laser flash method.

[1] Wong et al. A review of state-of-the-art thermal diodes and their potential applications. Int. J. Heat Mass Transf. 164, 120607 (2021)
[2] Aryana et al. Observation of solid-state bidirectional thermal conductivity switching in antiferroelectric lead zirconate (PbZrO3), Nat. Commun. 13, 1573 (2022)
[3] Nataf et al. Domain-wall engineering and topological defects in ferroelectric and ferroelastic materials. Nat. Rev. Phys. 2, 634–648 (2020)

Contexte de travail

The PhD student will work in the GREMAN laboratory (UMR CNRS 7347), which has strong expertise in ferroelectric oxides (from their growth to their integration into devices, including their complete characterization) and in the measurement and modeling of thermal transport. They will mainly work in the city of Blois, but will be required to perform some measurements on the CERTeM platform in the city of Tours (http://certem.univ-tours.fr/). This project is part of the ERC Starting Grant "DYNAMHEAT".

During the PhD thesis, the student will have the opportunity to spend time in several international laboratories: University of Cambridge, University of Darmstadt, University of Luxembourg.

Informations complémentaires

The candidate must hold a Master's degree or an engineering degree in Physics, Chemistry or Materials Science. Motivated and dynamic student with strong abilities for experimental work, a good knowledge of English (written and oral) as well as strong writing skills. An internship experience in a research laboratory will be appreciated.

The recruitment process by GREMAN (UMR CNRS 7347) takes place in 2 stages.
1) Preselection (application deadline April 7, 2023): the candidate must send a cover letter (1 page maximum) and a detailed CV (with the contacts of one or two references), via the recruitment portal.

All applications will be reviewed and a selection of candidates will be invited to an interview at GREMAN (or online) by the scientific supervisors (Guillaume Nataf: guillaume.nataf@univ-tours.fr and Fabien Giovannelli: fabien.giovannelli@univ-tours.fr).

2) Interview by the scientific supervisors (April 2023, at GREMAN or online): each candidate will have 20 minutes to present their background and their motivation for the project, followed by 30 minutes of discussion.