| | | | | | | webmail : intra-extra| Accès VPN| Accès IST| Contact | English
Univ. Paris-Saclay

Sujet de stage / Master 2 Internship

Back to the internship list


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 characterization of the thermal relaxation of densified silica samples (high dose under irradiation and in the form of a thin layer). We will measure the evolution of glass density, refractive index and vibrational properties (Raman and infrared spectroscopy) after thermal treatments. One of the objectives will be to determine the distribution of activation energies of the so-called metamict phase in order to better characterize the transition between low and high-density amorphous states.

Internship duration: 4-6 months
Possibility of continuation in PhD: Oui
Deadline for application:10/04/2021

Full description:
Background: Nowadays, many technologies are based on optical or optoelectronic devices integrating silica glasses because of its outstanding properties (ultra-transparency in the UV-NIR range, high mechanical resistance, low thermal expansion). Understanding the behavior of silica under extreme conditions (high pressure, irradiation) remains an issue for a large number of applications in the nuclear and space fields. It is possible by indentation or hydrostatic compression to permanently densify silica up to limit values around 20% (at 25 GPa) due to the large free volume of this glass. Irradiation is also a means of densifying silica. We have recently shown the existence of a unique 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) [1-2]. But at this stage, it is unclear if this amorphous phase is unique and identical to the so-called "metamictic" phase obtained after irradiation and amorphisation of the crystalline polymorphs of silica (quartz, coesite...). One of the means to better characterize this phase is to study the relaxation of its structure and properties, following heat treatments.

Purpose of the internship: We will characterize the thermal relaxation of densified silica samples (high dose under irradiation and in the form of a thin layer). We will measure the evolution of glass density, refractive index and vibrational properties (Raman and infrared spectroscopy) after thermal treatments. One of the objectives will be to determine the distribution of activation energies of the so-called metamict phase in order to better characterize the transition between low and high density amorphous states.

Reference:
[1] 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.

[2] Unique silica polymorph obtained under electron irradiation
I. Reghioua, M. Lancry , O. Cavani, S. Le Floch , D- R. Neuville and N. Ollier Applied Physics Letters 115 (2019) 251101
Technics/methods used during the internship:
Thermal treatments, Raman and infra-rouge spectroscopies,

Laboratory
Tutor of the internship

 

Retour en haut