Probing disorder in pyrochlore oxides using in situ synchrotron diffraction from levitated solids-A thermodynamic...

Area of Science:

• Materials Science
• Solid State Chemistry
• Thermodynamics

Background:

• Pyrochlore oxides, derived from defect fluorite structures, exhibit complex disordering.
• Understanding this disorder is key for applications like nuclear waste management.

Purpose of the Study:

• To develop a thermodynamic model for pyrochlore disordering enthalpies.
• To correlate experimental site distribution data with theoretical predictions.

Main Methods:

• In situ high-temperature synchrotron X-ray diffraction.
• Analysis of site occupancies in RE2Zr2O7 pyrochlores (RE = Sm, Eu, Gd).
• Thermodynamic modeling of disordering enthalpies.

Main Results:

• Disordering increases with temperature, especially near the fluorite phase transition.
• Cation disorder enthalpy correlates with rare earth ion radius; oxygen disorder enthalpy is constant.
• Experimental enthalpies are less endothermic than ab initio predictions.
• Thermal expansion coefficients range from 8.6-10.8 × 10⁻⁶ K⁻¹.

Conclusions:

• The study provides experimental defect formation energies for pyrochlores.
• Findings enhance understanding of pyrochlore stability and disordering mechanisms.
• Results are vital for optimizing pyrochlore use in nuclear waste immobilization.