Atomistic origin of structural relaxation in lead metasilicate and lithium disilicate glasses

• Grant number: 22/07679-8
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: November 30, 2022
• End date: November 29, 2023
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Edgar Dutra Zanotto
• Grantee: Ricardo Felipe Lancelotti
• Supervisor: Sabyasachi Sen
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Institution abroad: University of California, Davis (UC Davis), United States
• Associated to the scholarship: 21/03374-5 - Structural relaxation of glass and its influence on other dynamic processes, BP.DR

Abstract

Glasses are thermodynamically unstable materials. Hence, they spontaneously relax towards the supercooled liquid state. The structural relaxation process is an irreversible, time-dependent phenomenon, which may be experimentally detected by measuring some property over time at temperatures close to the laboratory glass transition. Even though the kinetics of the structural relaxation process during physical aging of glass is already reasonably known, its atomic-scale understanding remains elusive. A few atomistic simulations and experiments have been used to study this phenomenon with no universal results so far. Therefore, this project aims to carry out an in-depth study of the structural changes that occur in glasses during relaxation. We plan to use lead metasilicate and lithium disilicate glasses as model compositions (compositions used in the candidate´s PhD project), which already have a large volume of data on the structural relaxation kinetics. To this end, we will perform Raman and Nuclear Magnetic Resonance spectroscopic measurements on several samples with different fictive temperatures to track the time-dependent evolution of various structural parameters, including the symmetry of the Pb (or Li) and Si sites from the chemical shift anisotropy (or, quadrupolar coupling constant), change in the bond lengths and angles associated with the nearest neighbor coordination environments. On species disproportionation, etc. Very few works have addressed these aspects systematically in aging studies, which is vital for advancing the fundamental understanding of structural relaxation of glasses. (AU)