Periodic Reporting for period 1 - DYNAMHEAT (Ferroic Materials for Dynamic Heat Flow Control)
Période du rapport: 2023-01-01 au 2025-06-30
Tackling climate change is one of the most pressing challenges of our modern society and requires researching new refrigeration and renewable energy systems. Performances of all these systems could be significantly improved if they were combined with solid-state thermal switches and diodes. Current strategies that require to nanostructure materials or to operate in the vicinity of a phase transition, lead to thermal switches or thermal diodes with low efficiencies or not suitable for applications where space is limited. Furthermore, once designed, thermal properties of these elements are set and cannot be modified.
My objective is to investigate a fundamentally new mechanism to design compact and efficient thermal switches and diodes. My strategy exploits, in ferroelectric and ferroelastic oxides, the interactions between phonons and spontaneously occurring planar defects known as domain walls. Domain walls can be easily generated, moved, and oriented by application of a small voltage or a small uniaxial pressure, and interact with phonons as defects do. They are thus perfect interfaces to achieve large and reconfigurable anisotropies in thermal conductivities in controlled directions in a fast and reversible way.
In this ambitious project, I develop a novel approach to demonstrate a dynamic heat flow control through (i) the reversible engineering of the density of domain walls in desired directions, and (ii) the development of advanced experimental techniques for in-operando thermal characterizations. My multidisciplinary strategy will unravel the interactions between phonons and domain walls to reach higher thermal conductivity variations, and lead to ground-breaking thermal switches and diodes. These thermal switches and diodes will be compatible with a large range of devices and have an impact in many fields critical for our transition toward a sustainable future (e.g. solid-state refrigeration, solar panels, thermoelectric devices).
My objective is to investigate a fundamentally new mechanism to design compact and efficient thermal switches and diodes. My strategy exploits, in ferroelectric and ferroelastic oxides, the interactions between phonons and spontaneously occurring planar defects known as domain walls. Domain walls can be easily generated, moved, and oriented by application of a small voltage or a small uniaxial pressure, and interact with phonons as defects do. They are thus perfect interfaces to achieve large and reconfigurable anisotropies in thermal conductivities in controlled directions in a fast and reversible way.
In this ambitious project, I develop a novel approach to demonstrate a dynamic heat flow control through (i) the reversible engineering of the density of domain walls in desired directions, and (ii) the development of advanced experimental techniques for in-operando thermal characterizations. My multidisciplinary strategy will unravel the interactions between phonons and domain walls to reach higher thermal conductivity variations, and lead to ground-breaking thermal switches and diodes. These thermal switches and diodes will be compatible with a large range of devices and have an impact in many fields critical for our transition toward a sustainable future (e.g. solid-state refrigeration, solar panels, thermoelectric devices).
During this reporting period, I have recruited and trained a team of highly motivated PhD students and research associates. My research team has developed several strategies to reversibly engineer the density of domain walls in ferroelectric and ferroelastic materials, designed bespoke advanced experimental techniques for in-operando thermal characterizations, and demonstrated state-of-the-art performances of thermal conductivity switches.
In particular:
We showed that ferroelastic domain walls behave as boundaries that act like efficient controllers to govern thermal conductivity. At low temperature (3 K), we demonstrated a fivefold reduction in thermal conductivity induced by domain walls orthogonal to the heat flow and a twofold reduction when they were parallel to the heat flow. By breaking down phonon scattering mechanisms, we also analysed the temperature dependence of the thermal conductivity to derive a quantitative relation between thermal conductivity variations and domain wall organization and density. This work has led to a publication in Physical Review B [Phys. Rev. B 108, 144104 (2023)].
We predicted by ab initio electronic structure calculations that ferroelectric domains in barium titanate exhibit anisotropic thermal conductivities and confirmed this prediction by advanced thermal conductivity characterizations on a single crystal of barium titanate. We then used this gained knowledge to propose a lead-free thermal conductivity switch without inactive material, operating reversibly with an electric field. This work has led to a publication in Physical Review Materials [Phys. Rev. Mater. 8, 094403 (2024)].
In particular:
We showed that ferroelastic domain walls behave as boundaries that act like efficient controllers to govern thermal conductivity. At low temperature (3 K), we demonstrated a fivefold reduction in thermal conductivity induced by domain walls orthogonal to the heat flow and a twofold reduction when they were parallel to the heat flow. By breaking down phonon scattering mechanisms, we also analysed the temperature dependence of the thermal conductivity to derive a quantitative relation between thermal conductivity variations and domain wall organization and density. This work has led to a publication in Physical Review B [Phys. Rev. B 108, 144104 (2023)].
We predicted by ab initio electronic structure calculations that ferroelectric domains in barium titanate exhibit anisotropic thermal conductivities and confirmed this prediction by advanced thermal conductivity characterizations on a single crystal of barium titanate. We then used this gained knowledge to propose a lead-free thermal conductivity switch without inactive material, operating reversibly with an electric field. This work has led to a publication in Physical Review Materials [Phys. Rev. Mater. 8, 094403 (2024)].
During this reporting period, my research team has made excellent progress on all the activities planned. We have discovered a number of strategies to design thermal conductivity switches that exceed the performance of state-of-the-art alternatives. I expect to unravel the interaction between phonons and domain walls and to improve even more the performance of our thermal conductivity switches, in terms of thermal conductivity ratio and operating temperature range.