Compositional engineering of lanthanum-modified barium–strontium borate glasses with enhanced thermal and gamma-shielding performance

Lanthanum substitution was investigated in 10BaO–10SrO–(80−n)B₂O₃–nLa₂O₃ glasses, where n = 0–15 mol%, to clarify how replacing B₂O₃ with La₂O₃ affects structure, thermal behaviour, density, and gamma-ray shielding in one barium–strontium borate series. The glasses were prepared by melt quenching and remained fully amorphous by X-ray diffraction. Infrared analysis showed an initial increase in tetrahedral borate units at low and intermediate La₂O₃ contents, followed by partial network depolymerisation at higher substitution. Thermal and physical properties changed strongly with composition: the coefficient of thermal expansion increased from 6.58 to 7.92 ppm/°C, the dilatometric softening temperature from 582 to 664 °C, the glass-transition temperature from 541 to 643 °C, and the density from 2.71 to 3.85 g/cm³. Gamma-ray shielding parameters were calculated using Phy-X from the measured density and glass composition over 0.284–2.506 MeV. At 0.662 MeV, the linear attenuation coefficient increased from 0.204 to 0.296 cm−¹, while the half-value layer decreased from 3.39 to 2.34 cm. The results show that La₂O₃ substitution provides a clear route to strengthen gamma-shielding performance while preserving glass formation and improving thermal resistance.