Ab initio calculation of excess properties of La1−x(Ln,An)xPO4 solid solutions

Abstract We used ab initio computational approach to predict the excess enthalpy of mixing and the corresponding regular/subregular model parameters for La 1 − x Ln x PO 4 ( Ln =Ce,…, Tb) and La 1 − x An x PO 4 ( An =Pu, Am and Cm) monazite-type solid solutions. We found that the regular model interaction parameter W computed for La 1 − x Ln x PO 4 solid solutions matches the few existing experimental data. Within the lanthanide series W increases quadratically with the volume mismatch between LaPO 4 and Ln PO 4 endmembers ( Δ V = V LaPO 4 − V Ln PO 4 ) , so that W ( kJ / mol ) = 0.618 ( Δ V ( cm 3 / mol ) ) 2 . We demonstrate that this relationship also fits the interaction parameters computed for La 1 − x An x PO 4 solid solutions. This shows that lanthanides can be used as surrogates for investigation of the thermodynamic mixing properties of actinide-bearing solid solutions.