A Molecular Dynamics-Based Extended DFTB Analysis of Tm─Te Bonding Interactions Role on Crystallinity and Diffusion Process in Bismuth Boro-tellurite Glass Modified with Tm2O3

Abstract

This study presents a comprehensive theoretical investigation into a newly fabricated bismuth boro-tellurite glass activated by thulium (Tm), with compositions of (50-x)B₂O₃ + 30TeO₂ + 10Bi₂O₃ + 10CdO + xTm₂O₃ (x = 0 and 5 mol%), labeled as BiBT-Tm0 and BiBT-Tm5, respectively. The calculations were conducted using molecular dynamics simulations via the extended density functional tight-binding (GFN1-xTB) method based on density functional theory (DFT). X-ray diffraction patterns (XRD), densities, partial radial distribution functions (PRDF), time-dependent mean-square displacement (MSD), self-diffusion coefficients, and glass transition temperatures (T_g) at 30 and 350°C were evaluated for each glass sample during the annealing process. According to PRDF results, the first peak for the B–Te pair, which observed at 2.23 Å decreased significantly with the increasing Tm content with the formation of strong Tm─Te interactions. The diffusion coefficient of Te increased by 570% with Tm addition. The diffusion coefficient of Tm increased from 0.0212 to 0.15 (10⁻⁹ m/s) when temperature increases from 30°C to 350°C. In addition, Tg increased with Tm₂O₃ content, ranging from 75 to 150°C. Also, crystallite size from XRD data by using Debye–Scherrer analysis was calculated as 9.92 and 20.6 nm for BiBT-Tm0 and BiBT-Tm5, respectively.