Technetium incorporation in scheelite: insights from first-principles

Atomistic investigations of crystalline scheelite, CaWO₄, and ⁹⁹Tc-bearing scheelite, CaWO₄:Tc, have been carried out using density functional theory. The lattice constants, bulk modulus, and volume compression data of CaWO₄ have been calculated and compared with experimental data, with a focus on predictive understanding of ⁹⁹Tc incorporation in CaWO₄. Defect formation energies have been computed for several possible interstitial (I) and substitutional (S) sites of ⁹⁹Tc in CaWO₄. Both I(O_h) and S(W) sites were found to be energetically favourable for Tc doping. X-ray diffraction (XRD) spectra for each ⁹⁹Tc defect type have been simulated to help interpret the complex experimental XRD patterns. This work on CaWO₄:Tc provides insights into materials generated during nuclear weapons testing and useful spectral signatures for nuclear forensics.