Structural compaction and enhanced gamma-ray shielding performance of CdO-modified zinc borate glasses

CdO-modified zinc borate glasses with composition 60B₂O₃–1CuO–xCdO–(39 − x)ZnO (x = 0–10 mol%) were prepared using the conventional melt-quenching technique. The effect of progressive CdO-for-ZnO substitution on the structural, physical, optical, and gamma-ray shielding properties was systematically investigated. XRD analysis confirmed the amorphous nature of all compositions, while FTIR analysis revealed an increase in the BO₃ fraction from 0.553 to 0.577 accompanied by a decrease in N₄ from 0.447 to 0.423, indicating a redistribution toward BO₃-rich configurations. The density increased from 3.510 to 4.030 g/cm³, whereas the molar volume decreased from 39.17 to 31.28 cm³/mol, demonstrating enhanced structural compactness. The accompanying reductions in oxygen molar volume and oxygen free volume further indicated more efficient oxygen packing. The indirect optical band gap gradually decreased from 3.34 to 3.05 eV with increasing CdO content, reflecting composition-induced changes in the local electronic structure. Gamma-ray shielding calculations using Phy-X/PSD showed improved attenuation performance for CdO-rich compositions, as evidenced by higher attenuation coefficients and lower HVL, TVL, and MFP values. The enhanced shielding performance is attributed to the combined effect of the higher atomic number of Cd and enhanced glass network compactness. The systematic correlation established among borate structural evolution, packing compactness, optical band-gap modification, and gamma-ray attenuation highlights the significance of controlled CdO-for-ZnO substitution and supports the potential of these glasses as lead-free radiation shielding materials.