title: Real-time observation of the isothermal crystallization kinetics in a deeply supercooled liquid.
abstract: Below the melting temperature Tm, crystals are the stable phase of typical elemental or molecular systems. However, cooling down a liquid below Tm, crystallization is anything but inevitable. The liquid can be supercooled, eventually forming a glass below the glass transition temperature Tg. Despite their long lifetimes and the presence of strong barriers that produces an apparent stability, supercooled liquids and glasses remain intrinsically a metastable state and thermodynamically unstable towards the crystal. Here we investigated the isothermal crystallization kinetics of the prototypical strong glassformer GeO2in the deep supercooled liquid at 1100 K, about half-way between Tmand Tg. The crystallization process has been observed through time-resolved neutron diffraction for about three days. Data show a continuous reorganization of the amorphous structure towards the alpha-quartz phase with the final material composed by crystalline domains plunged into a low-density, residual amorphous matrix. A quantitative analysis of the diffraction patterns allows determining the time evolution of the relative fractions of crystal and amorphous, that was interpreted through an empirical model for the crystallization kinetics. This approach provides a very good description of the experimental data and identifies a predator-prey-like mechanism between crystal and amorphous, where the density variation acts as a blocking barrier.
authors.affiliation: Dipartimento di Informatica, Università di Verona, I-37134 Verona, Italy.|ISC-CNR c/o Dipartimento di Fisica, Sapienza Università di Roma, I-00185 Roma, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Zanatta
authors.affiliation: Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités, UPMC Université Paris 06, CNRS UMR 7590, Muséum National d'Histoire Naturelle, IRD UMR 206, F-75005 Paris, France.
authors.forename: L
authors.initials: L
authors.lastname: Cormier
authors.affiliation: Conditions Extrêmes et Matériaux: Haute Température et Irradiation, CEMHTI-CNRS, Université d'Orléans, F-45071 Orléans, France.|Laboratoire Léon Brillouin, CEA-CNRS, CEA Saclay, F-91191 Gif sur Yvette, France.
authors.forename: L
authors.initials: L
authors.lastname: Hennet
authors.affiliation: Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia, Italy.|IOM-CNR c/o Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Petrillo
authors.affiliation: Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia, Italy.|IOM-CNR c/o Dipartimento di Fisica e Geologia, Università di Perugia, I-06123 Perugia, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Sacchetti