L'Association Européenne de Cristallographie (ECA) a lancé le 10 juin 2021 les "webinaires déjeuner". Les groupes d'intérêt spéciaux (SIG) et les groupes d'intérêt général (GIG) de l'ECA organisent à tour de rôle un webinaire adapté à la communauté des cristallographes au sens large. Le septième webinaire sera diffusé le 13 janvier 2022 (13h) et est organisé par SIG-11 - Crystallography under extreme conditions. Le thème de ce webinaire est Adventures in Pressure-Temperature Space (Kamil Dziubek, European Laboratory for Non-Linear Spectroscopy / University of Florence, Italy). Inscriptions ici.


According to the Oxford English Dictionary a phase diagram is “a diagram which represents the limits of stability of the various phases of a chemical system at equilibrium, with respect to two or more variables.” In high-pressure research these variables are most commonly referred to as temperature and pressure, for a given chemical composition. This definition, however, does not apply to the majority of simple molecular compounds consisting of light elements, including almost all organic compounds. These systems are metastable at any given thermodynamic conditions, as they never correspond to the Gibbs free energy minimum. In spite of that, metastable states are often promising technological materials. Moreover, dynamic compression experiments have recently demonstrated how the experimentally observed phase boundaries depend on transition kinetics. Hence, navigating the energetic landscape of highly polymorphic systems can lead to ‘dynamic phase diagrams’ or ‘metastable phase diagrams’ (transitional diagrams), which do not conform to the quoted definition, but can be extremely interesting for technological applications or fundamental studies. Throughout the talk, concepts will be illustrated by use cases from literature and own research.

 

 

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