Accueil >
Production scientifique
Physique des Verres
(3) Production(s) de l'année 2021
|
|
Percolation transitions in compressed SiO2 glasses 
Auteur(s): Hasmy A. , Ispas S., Hehlen B.
(Article) Publié:
Nature, vol. 599 p.62 (2021)
DOI: 10.1038/s41586-021-03918-0
Résumé: Amorphous–amorphous transformations under pressure are generally explained by
changes in the local structure from low- to higher-fold coordinated polyhedra1–4.
However, as the notion of scale invariance at the critical thresholds has not been
addressed, it is still unclear whether these transformations behave similarly to true
phase transitions in related crystals and liquids. Here we report ab initio-based
calculations of compressed silica (SiO2) glasses, showing that the structural changes
from low- to high-density amorphous structures occur through a sequence of
percolation transitions. When the pressure is increased to 82 GPa, a series of
long-range (‘infinite’) percolating clusters composed of corner- or edge-shared
tetrahedra, pentahedra and eventually octahedra emerge at critical pressures and
replace the previous ‘phase’ of lower-fold coordinated polyhedra and lower
connectivity. This mechanism provides a natural explanation for the well-known
mechanical anomaly around 3 GPa, as well as the structural irreversibility beyond
10 GPa, among other features. Some of the amorphous structures that have been
discovered mimic those of coesite IV and V crystals reported recently5,6, highlighting
the major role of SiO5 pentahedron-based polyamorphs in the densification process of
vitreous silica. Our results demonstrate that percolation theory provides a robust
framework to understand the nature and pathway of amorphous–amorphous
transformations and open a new avenue to predict unravelled amorphous solid states
and related liquid phases7,8.
|
|
|
|
Importance of lattice softness and phonon anharmonicity for the optoelectronic properties of 3D, 2D and 0D halide perovskites
Auteur(s): Even Jacky, da Cunha Ferreira Afonso, Paofai Serge, Létoublon Antoine, Ollivier Jacques, Raymond Stéphane, Sébastien Clément, Vialla R., Hehlen B., Ruffle B., Cordier Stéphane, Katan Claudine, Bourges Philippe
Conference: Journées de la diffusion neutronique (grenoble, FR, 2021-09-20)
|
|
|
|
Raman resonance tuning of quaterthiophene in filled carbon nanotubes at high pressures
Auteur(s): Alencar R. S., Aguiar A. L., Ferreira R. S., Chambard R., Jousselme B., Bantignies J.-L., Weigel C., Clement S., Aznar R., Machon D., Souza Filho A. G., San-Miguel A., Alvarez L.
(Article) Publié:
Carbon, vol. 173 p.163-173 (2021)
Texte intégral en Openaccess : 
Ref HAL: hal-03163018_v1
DOI: 10.1016/j.carbon.2020.10.083
WoS: WOS:000613132200003
Exporter : BibTex | endNote
Résumé: Filling carbon nanotubes with molecules is a route for the development of electronically modified one-dimensional hybrid structures for which the interplay between the electronic structure of molecules and nanotubes is a key factor. Tuning these energy levels with external parameters is an interesting strategy for the engineering of new devices and materials. Here we show that the hybrid system composed by quaterthiophene (4T) molecules confined in single-walled carbon nanotubes, presents a piezo-Raman-resonance of the molecule vibrational pattern. This behavior manifests as a rapid pressure induced enhancement of the 4T Raman mode intensities compared to the tubes G-band Raman modes. Density functional theory calculations allow to explain the spectral behaviour through the pressure-enhanced quaterthiophene resonance evolution. By increasing pressure, the tube cross-section deformation leads to a reduction of the intermolecular distance, to the splitting of the molecular levels and then to an increase of resonance channels. Calculations and experiments converge to the 4T piezo-resonance scenario associated with the pressure-induced nanotube radial collapse observed at about 0.8 GPa. Our findings offer possibilities for the development of pressure transducers based on molecule-filled carbon nanotubes.
|
