Influence of crystal tetrahedral and octahedral voids on the radiation shielding properties of iron-based spinels

This study investigates six iron-based spinel compounds (Fe₃O₄, MnFe₂O₄, NiFe₂O₄, CoFe₂O₄, ZnFe₂O₄, and CuFe₂O₄) as potential candidates for radiation shielding materials. Using the NIST XCOM photon cross-sections (cross-checked with Phy-X/PSD) across 0.015–15 MeV, key shielding parameters were evaluated, including mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP). Additionally, atomistic parameters such as the effective atomic number (Z_eff), electron density (N_eff), and equivalent atomic number (Z_eq) were assessed. Attenuation metrics were related to density and crystallographic descriptors—tetrahedral (V_tet) and octahedral (V_oct) void volumes and the lattice void ratio (R)—together with ionic site distribution. Calculations show a descending LAC trend as follows: ZnFe₂O₄ > CuFe₂O₄ > NiFe₂O₄ > CoFe₂O₄ > MnFe₂O₄ > Fe₃O₄. A positive correlation between density and LAC was identified, accompanied by a reduction in HVL and TVL values. Furthermore, at sub-MeV energies, MAC shows a qualitative (monotonic) increase with decreasing V_tet/V_oct and lower R, consistent with denser electronic packing. Among the compounds analysed, CuFe₂O₄ and ZnFe₂O₄ demonstrated the highest shielding performance in attenuation capability and material thickness efficiency. Since the dataset comprises six compositions (n = 6), these structure–property relationships are reported as descriptive trends rather than fitted correlations. These findings highlight the critical influence of crystallinity and ionic distribution within the unit cell on the effectiveness of radiation shielding materials, providing actionable targets (smaller V_tet/V_oct and lower R) for designing durable, lead-free shields.