Abstract
Multi-cation substituted pyrochlores are potential matrices for immobilization of long-lived high level nuclear waste. In this paper, we report, the structural and thermodynamic stabilities of aliovalent multi cation substituted Gd2Ti2O7 pyrochlore compounds determined by experimental and theoretical methods. A series of cubic pyrochlore-type Gd2-2xCaxZrxTi2O7 (0.0 ≤ x ≤ 0.4) compounds were synthesized and characterized by XRD and Raman spectroscopy techniques. It is observed that incorporation of Ca2+ and Zr4+ at Gd3+ site does not significantly alter crystal lattice of Gd2Ti2O7. Calorimetric studies were carried out to determine the thermodynamic stability of Gd2-2xCaxZrxTi2O7 compounds. The observed data indicate that standard molar enthalpy of formation of Gd2-2xCaxZrxTi2O7 decreases steadily with increasing dopant concentration which has been attributed to increasing distortion of the polyhedra around the cations. These inferences were further supported by DFT calculations.
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