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

This study presents a comprehensive theoretical investigation into a newly fabricated bismuth boro‐tellurite glass activated by thulium (Tm), with compositions of (50‐ x )B 2 O 3 + 30TeO 2 + 10Bi 2 O 3 + 10CdO + x Tm 2 O 3 ( 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 Tm 2 O 3 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.