Predicting the Thermodynamic Stability of (Gd1−xLnx )2SiO5 and (Lu1−xLnx )2SiO5 Solid Solutions of the P21/c Space Group.

Within the framework of V. S. Urusov’s crystal-energy theory of isomorphous substitutions, the mixing energies (interaction parameters) and critical decomposition (stability) temperatures are calculated for the (Gd_1-xLn_x )₂SiO₅ systems, where Ln represents rare-earth elements (REEs) or yttrium. The values of the total mixing energies are determined mainly by contributions arising from the difference in sizes of the substituting structural units. The contributions due to differences in the degree of ionicity of the chemical bond between the components are significantly smaller and can be neglected in most cases. Diagrams of the thermodynamic stability of systems (Gd_1-xLn_x )₂SiO₅ and decomposition domes of the (Gd_1-xLn_x )₂SiO₅ and (Lu_1-xLn_x )₂SiO₅ systems are presented, which allow for graphical prediction of decomposition temperatures of solid solutions within the specified substitution limits, equilibrium substitution limits at a given temperature, and ranges of thermodynamic stability for solid solutions. The predictions of thermodynamic stability are consistent with experimental data previously reported in the literature for solid solutions based on doped gadolinium oxyorthosilicate. The gadolinium oxyorthosilicate solid solutions, which exhibit luminescent, scintillation, and other practically important properties, due to their very low critical decomposition temperatures and a wide temperature range of thermodynamic stability compared to solid solutions of oxyorthosilicate of other REEs, can find practical applications as nanomaterials. [ABSTRACT FROM AUTHOR]