BaO-modified lead-free borate glasses: Structural, optical, and radiation shielding enhancements

In this study, a series of borate-based glasses with the composition (55-x)B₂O₃–7MgO–14ZnO-xBaO-1Sm₂O₃ (x = 23, 27, 31, and 35 mol%) were synthesized using the conventional fast-cooling process to examine the impact of BaO incorporation on their various properties. As BaO content increased, both glass density (3.950–4.291 g/cm³) and molar volume (23.104–23.608 cm³/mol) rose. FTIR analysis confirmed the evolution of the borate network, with intensified bands related to BO₄ and BO₃ units and the emergence of Ba–O vibrations, indicating disrupted connectivity. Mechanically, increasing BaO weakened the glass network, reducing parameters such as Young's modulus (from 108.494 to 93.385 GPa) and microhardness (from 4.983 to 4.667 GPa), which is consistent with lower bond strength and decreased compactness. Optically, a redshift in the UV–Vis absorption edge was observed, along with a decline in both the direct (from 3.016 to 2.801 eV) and indirect (from 2.931 to 2.272 eV) optical bandgaps, while Urbach energy increased from 0.311 to 0.347 eV, reflecting higher structural disorder. Radiation shielding analysis revealed that higher BaO levels enhanced the linear attenuation coefficients (LACs) at 0.015 MeV, from 133.567 to 174.656 cm⁻¹, correlating with their respective BaO content and density. For mass attenuation coefficients (MACs), BMZS4 exhibited the highest values at 0.015 MeV (40.703 cm²/g), while the values decreased exponentially with energy increase. The effective atomic number (Z_eff) for BMZS4 started at 44.76 at 0.015 MeV and exhibited a decreasing trend with energy, signifying its superior shielding strength. Sample BMZS4 (35 mol% BaO) exhibited the lowest mean free path (MFP) and tenth value layer (TVL), making it the most effective in radiation shielding. Across all energy ranges, BMZS4 consistently outperformed the other compositions due to its higher density and BaO content. Comparative HVL analysis showed that BMZS2-4 glasses offer superior shielding capability over some conventional glass systems at 0.40 MeV. These findings suggest that increasing BaO content systematically modifies the glass network, facilitating application-specific tuning, particularly in optical and radiation protection domains where transparent materials are required.