Thèses

Jeudi 21 Décembre 2017 à 10h30.

The effect of a partial nanocrystallization on the transport properties of amorphous/crystalline composites

''Face to the growing technological needs in the modern society, the need has arisen of developing novel multifunctional materials, able to simultaneously assure different functions. This is especially important in advanced technologies, such as microelectronics and energy harvesting, where heat dissipation reduction is essential, while keeping good electrical properties. Optimizing such materials represents however a challenging task: lowering thermal conductivity generally implies lowering the electrical conductivity as well. A new strategy has recently aroused consisting in exploiting heterogeneous materials at the nanoscale, so-called “nanocomposites”. Despite their great potential, the fundamental understanding of their properties is still lacking. In this thesis, we present a fundamental investigation of the transport properties in composites made of nano-inclusions embedded in an amorphous matrix, aimed to get a microscopic insight into the mechanisms ruling transport in such materials. To this purpose, we have carried on an experimental study in two intermetallic composites, based on a metallic glass and a chalcogenide glass, where crystalline inclusions were directly obtained from the glass temperature-induced recrystallization. Our investigation, combining macroscopic and microscopic measurements, has revealed that transport behavior is strongly dependent on the properties contrast between the amorphous matrix and the crystalline inclusions. Our findings are comforted by our theoretical results, obtained by molecular dynamics simulations on a model composite system, which highlight the effect of the rigidity contrast on the vibrational properties of such material, and thus on thermal transport.''