Dissolution of Impurities in Sodium–Gadolinium Molybdate NaGd(MoO4)2

Impurity defects in sodium–gadolinium molybdate NaGd(MoO₄)₂ have been investigated by the method of interatomic potentials. The solution energies of tri-, di-, and monovalent impurities are estimated. The dependences of the solution energy on the impurity ionic radius are plotted. For heterovalent substitutions, the most energetically favorable mechanism of charge compensation is found, both due to intrinsic crystal defects and according to the conjugate isomorphism scheme. The positions of the most likely localization of defects are determined. The influence of the disordering of sodium and gadolinium ions on the positional differences in the energy of defects is estimated. A comparison of the solubility of impurities in NaGd(MoO₄)₂ and CaMoO₄ (a compound isostructural to it) indicates that, although isovalent substitutions are energetically more favorable than heterovalent ones, the mechanism of conjugate isomorphism (providings electrical neutrality) can equalize these processes.