Microscopic structure of lead-silicate glass and its correlation with thermal, mechanical, and radiation shielding properties

P Sahu and MA Sheikh, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 131, 935 (2025).

DOI: 10.1007/s00339-025-08983-0

Lead-silicate glasses are widely used in radiation shielding windows (RSW) as they offer high density and ability to attenuate gamma-rays and X-rays while maintaining optical transparency. A detailed atomistic understanding is of importance for its wide technological applications. Therefore, classical molecular dynamics (MD) simulations in conjunction with ab initio MD (AIMD) simulation are carried out for binary lead silicate glasses with 30, 50, and 64 mol% PbO to elucidate the structure-property relationships. The calculated results show a 48.42% density increase and a significant rise in non-bridging oxygens (NBOs) confirming the network-modifying role of Pb2+ ions. The network modifying role of Pb2+ ions is also supported by Q(4)/Q(3) to Q(0)/Q(1) conversion and by the presence of multiple PbOn (n = 1-7) geometries with average similar to 4-fold coordination. The emergence of a structure factor peak at 2.96 angstrom(-1) and cluster size analysis indicate Pb clustering and a tendency to form a percolating network at a higher PbO concentrations. The formation of 2-8 membered Pb-O-Pb-O rings and the increasing intensity in total VDOS at 150 cm(-1) suggest the partial covalent Pb-O network formation at higher PbO levels. Altogether, the results suggest that Pb2+ ions though primarily act as network modifiers, nevertheless, some Pb2+ ions may potentially integrate into the glass network structure at higher concentrations. These microscopic features explain the observed 16.68% decrease in T-g; 62.5% increase in the thermal expansion coefficient (TEC) and 19.49% rise in Young's modulus (Y) while increasing PbO from 30 to 64 mol%. Thermodynamic analysis via two-phase thermodynamic (2PT) model reveals a 53.29% increase in vibrational entropy and a 106.52% increase in configurational entropy, supporting Pb-induced network depolymerization. The optical analysis demonstrates a 15.34% increase in refractive index, and 32.15% increase in dielectric constant with increasing PbO from 30 to 64%, while the reflection loss is increased from 7.62% to 11.53% due to higher density and more NBOs creation. The radiation shielding evaluations confirm that glasses with higher PbO content exhibit superior photon attenuation efficiency, particularly against low-energy photons dominated by photoelectric interactions.

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