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Examining Order-Disorder Structural Transition of Gd2Zr2-CeO7 Using Synchrotron Techniques
Khushveer Kaur1, Graham King2, Andrew P Grosvenor1
1Department of Chemistry, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5C9, Canada.
Inorganic Chemistry
|March 19, 2025
Summary
This study investigates the crystal structure transitions in gadolinium zirconate by substituting cerium. Synchrotron X-ray diffraction revealed distinct structural phases, clarifying previous research ambiguities.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Crystallography
Background:
- A2B2O7-type oxides exhibit diverse crystal structures (pyrochlore, defect fluorite, bixbyite) influenced by cation radius ratios.
- Gadolinium zirconate (Gd2Zr2O7) shows polymorphic transitions between pyrochlore and defect fluorite structures.
- Previous structural analyses of substituted Gd2Zr2O7 faced challenges due to weak superstructural peaks in conventional X-ray diffraction (XRD).
Purpose of the Study:
- To investigate the structural evolution of Gd2Zr2-xCexO7 (0 ≤ x ≤ 2) ceramics.
- To clarify the polymorphic transitions by employing high-resolution synchrotron XRD.
- To determine the oxidation states of Ce and Zr cations in the synthesized materials.
Main Methods:
- Synthesis of Gd2Zr2-xCexO7 powders via a coprecipitation method followed by annealing at 1400 °C.
- High-resolution structural analysis using synchrotron X-ray diffraction (XRD).
- X-ray absorption near edge spectroscopy (XANES) at Ce L3 and Zr K-edges to determine cation oxidation states.
Main Results:
- Synchrotron XRD data identified phase mixtures of defect fluorite and pyrochlore for x = 0-0.25.
- The defect fluorite structure was predominant for x = 0.5-1.75.
- The bixbyite structure was observed exclusively at x = 2.
- XANES spectra confirmed that both Ce and Zr cations existed in the 4+ oxidation state across all compositions.
Conclusions:
- Synchrotron XRD successfully resolved structural ambiguities in Gd2Zr2-xCexO7, revealing distinct phase transitions with increasing Ce content.
- The study provides a clear structural phase diagram for the Gd2Zr2-xCexO7 system.
- The findings contribute to understanding structure-property relationships in A2B2O7 oxides.
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