Pyrochlore-like Local Structure in Globally Disordered Y₂Zr₂O₇: Evidence and Reasoning by Combined Theoretical and...

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nuclear Engineering

Background:

• The Y2Zr2O7 system is technologically relevant for nuclear and oxide fuel cell applications.
• Its local atomic structure remains debated, with conflicting evidence from diffraction versus spectroscopic methods.
• A clear correlation between local and global structures in Y2Zr2O7 is currently lacking.

Purpose of the Study:

• To investigate the local structure of Y2Zr2O7 and its relationship with global structural disorder.
• To elucidate the atomic arrangement in Y2Zr2O7 using complementary experimental and computational techniques.
• To establish a link between local atomic ordering and the overall disordered nature of the Y2Zr2O7 phase.

Main Methods:

• X-ray Diffraction (XRD) for global structure analysis.
• Raman Spectroscopy and Electron Microscopy for structural characterization.
• Magic-Angle Spinning Nuclear Magnetic Resonance (MAS NMR) with Sn4+ probe ions.
• Photoluminescence (PL) spectroscopy with Eu3+ probe ions.
• Density Functional Theory (DFT) calculations.

Main Results:

• Globally disordered Y2Zr2O7 exhibits pyrochlore-like local structural features.
• 119Sn MAS NMR spectra indicate non-random cationic distribution, inconsistent with complete disorder.
• Eu3+ photoluminescence data suggest probe ion occupation at specific, potentially centrosymmetric sites.
• Crystal field splitting and lifetime measurements of Eu3+ further support ordered local arrangements.
• Discrepancies in Y-O and Zr-O bond strengths and characteristics are identified as the source of short-range ordering.

Conclusions:

• Y2Zr2O7, despite global disorder, possesses discernible pyrochlore-like local atomic arrangements.
• Short-range ordering arises from inherent bonding differences between Y-O and Zr-O bonds.
• These findings provide crucial insights for tailoring Y2Zr2O7 properties for targeted applications.