Dynamic heat flow control with ferroelectric domain walls – FLOW

Manipulating heat flows (phonons) remains a challenge, even though it is critical for the optimization of electronic circuits, solid-state refrigeration technologies, thermoelectric energy conversion and the development of a new paradigm of logic (phononics).

Recently, a strategy based on ferroelectric oxides has been suggested to obtain a dynamic heat flow control in a large temperature range, with expected thermal conductivity variations ~70%. Ferroelectrics spontaneously exhibit regions of uniform polarization, called domains, separated by nanometric interfaces, called domain walls. Polarizations can be switched, and thus the number of domains and their orientations controlled, by application of an electric field. Domain walls interact with phonons as ‘defects’ would. Thus, when increasing the density of domain walls, the number of phonons-domain walls collisions increases, and the thermal conductivity is reduced.

In the project we develop a unique approach based on thin films with thickness or composition gradients and advanced in-operando experimental techniques to engineer the ferroelectric domain structure and reach a dynamic control of thermal conductivity. The combination of the 3? method, scanning thermal microscopy and inelastic X-rays scattering under electric field, as well as the large temperature range on which measurements will be performed, demonstrate our objective to get a fundamental understanding of the interactions between domain walls and phonons. We will use the same techniques on several materials, take advantage of spontaneous changes in the domain structure with temperature and/or engineer the domain structure by thermal annealing or electric field to ensure robustness and reproducibility of the measurements.