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

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 LaPO4 and LnPO(4) endmembers (Delta V = V-LaPO4 - V-LnPO4), so that W(kJ/mol) = 0.618(Delta 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. (C) 2014 Elsevier Inc. All rights reserved.