Pressure Treated Glasses for Increased Thermal Conductivity

This program is financed by the Marie Sklodowska-Curie fellowship via the Polish National Science Centre, within the Horizon 2020 EU framework program under grant agreement No. 66577

Project Motivation: Crystals tend to conduct heat very well, with a diamond made out of carbon being the best conductor. The ability of crystal to conduct heat efficiently is associated with the motion of electrons or collective motion of atoms (or ions) in the form of propagating thermo-mechanical waves enabled by an ordered array of atoms/ions forming the crystal. However, atoms in glasses, such as oxide-based optical glasses rarely crystallize and exhibit very low thermal conductivity because there are few propagating thermal waves inside of them. Furthermore thermal conductivity of these glasses is not only low, but its range is also very narrow.

Project Description and Development: In our project we use computer models and simulations to explore a possibility that high pressure densified glasses might have much larger thermal conductivity than regular glasses. Computer simulations are used to create atomic models of glass structures with various pressures applied during structure generation and determination of thermal conductivity (Fig. 1). The simulation and theoretical consideration provide guidance for us to select composition and pressure conditions for experimental part of the program (Fig. 2). We synthesized oxide based glasses with a large boron enabling significant densification and atomic coordination change under pressures below 2 GPA allowing for pressure treatment of macroscopic samples. Currently with the use of IHPP facilities we densify macroscopic glass samples under a range of pressure and temperature protocols. We will determine structural characteristic and thermo-mechanical properties of these glasses, most prominently thermal conductivity. The experimental results will feed back to the modeling effort by verifying the predictions of simulation, and, if needed, by guiding the design of more accurate models.


Fig. 1. Thermal conductivity as a function of densification pressure determined for SiO2 glasses modeled with molecular dynamics	Fig. 2. Atomic configuration of (left) as-prepared and (right) 2 GPa hot compressed 24Li₂O-21Al₂O₃-55B₂O₃ glasses using prototypes of our new empirical potentials. For clarity, only oxygen and boron atoms are shown: 3-folded B in blue, 4-folded B in black, O in red.