Amorphisation sous pression dans les matériaux à coefficient de dilatation thermique négatif – PRESENT

The aim of this project is to investigate pressure-induced amorphisation (PIA) in negative thermal expansion materials (NTE). Negative thermal expansion materials are of great interest from both a fundamental and technological point of view. Negative thermal expansion has been linked to thermally excited rigid unit vibrational modes. These materials exhibit unusual behavior upon compression due to the softening of a large number of these modes leading to pressure-induced amorphization. Both negative thermal expansion and pressure-induced amorphization confer unique physical properties to these materials for technical applications in optical components and shock wave absorption, for example. The study will focus on two classes of materials with open structures exhibiting the highest known degree of negative thermal expansion: zeolites and cyanide compounds. Detailed structural and vibrational studies as a function of temperature and pressure using a variety of complementary spectroscopic and diffraction techniques will be performed, thereby probing the structural changes on different local and long-range length scales. These experimental results will be confronted with those obtained from ab initio calculations. Based on these results, new candidate materials will be targeted for synthesis. The goals will be to correlate NTE and PIA with the dynamical properties of these systems, identify new higher-performance materials, and to determine if their properties may be tuned by changing the chemical composition and/or introducing guest species in the case of porous structures.