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Thermal relaxation characterization of densified amorphous silica

Contact: OLLIER Nadège, , nadege.ollier@polytechnique.edu, +33 1 69 33 45 18
Summary:
This internship focuses on the identification and characterization of point defects in irradiated glasses mainly by EPR spectroscopy. It includes a glass synthesis part and characterization of defects. One of the aim is to use smartphone screens (Gorilla Glass) as potential "dosimeters" during accidental exposure to radiations.

Internship duration: 4-6 months
Possibility of continuation in PhD: Oui
Deadline for application:27/03/2020

Full description:
Background: Nowadays, many technologies are based on optical or optoelectronic devices integrating silica glasses because of its exceptional properties (ultra-transparency in the UV-NIR range, high mechanical resistance, low thermal expansion). Understanding the behavior of silica under extreme conditions (high pressures, irradiation) remains an issue for a large number of applications in the field of nuclear (ITER, nuclear fission, ...) and space. It is possible by indentation or by hydrostatic compression to permanently densify the silica to limit values around 20% (at 25 GPa) because of the large free volume of this glass. Densifying silica by using irradiation is also possible. We recently showed the existence of a single polymorph of silica (density 2.26 g / cm3) obtained whatever the initial state of the silica after irradiation at very high doses (typ> 10 GGy for electrons of 2.5 MeV) 1. But at this stage, it is unclear if this amorphous phase is unique and identical to the so-called "metamict" phase obtained after irradiation and amorphization of the crystalline polymorphs of silica (quartz, coesite, etc.). One way to better characterize this phase is to study the relaxation of its structure and its properties, following thermal treatments. This internship, which focuses on densified silica belongs to two different projects: an ANR project (currently being submitted) and a project in collaboration with CEA DRT, which aims to model the behavior of Bragg grating fiber sensors in extreme environment (radiation and / or high temperature).

Purpose of the internship: We will characterize the thermal relaxation of previously densified samples as well as that of the different silica samples densified and irradiated with electrons of 2.5 MeV to 11 GGy. We will measure the evolution of the glass density, the refractive index and its vibrational properties (Raman and infra-red spectroscopy) after thermal treatments. One of the objectives will be to determine activation energy distributions and better characterize the transition between amorphous states and in particular the metamict phase (amorphous phase of an initially crystalline solid).

Reference:
Relaxation study of pre-densified silica glasses under 2.5 MeV electron irradiation,
N. Ollier, M. Lancry, C. Martinet, V. Martinez, S. Le Floch, D. R. Neuville, Scientific reports (2019) 9:1227.
Technics/methods used during the internship:
Thermal treatments, Raman and infra-rouge spectroscopies,

Laboratory
Tutor of the internship

 

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