Anion disorder in lanthanoid zirconates Gd(2-x)Tb(x)Zr2O7.

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• The pyrochlore and defect fluorite phases in Ln2Zr2O7 (where Ln is a lanthanide) are known to exhibit order-disorder transitions.
• Understanding these transitions is crucial for applications involving advanced ceramic materials.

Purpose of the Study:

• To investigate the pyrochlore-defect fluorite order-disorder transition in Gd(2-x)Tb(x)Zr2O7 oxides.
• To determine the nature of the transition (abrupt vs. gradual) using multiple characterization techniques.

Main Methods:

• Synchrotron X-ray diffraction (XRD) for phase analysis.
• Neutron diffraction for detailed structural analysis, including sublattice ordering.
• X-ray absorption spectroscopy (XAS) at the Zr L3-edge to probe local coordination environments.

Main Results:

• Synchrotron XRD suggested an abrupt phase transition, while neutron diffraction indicated a gradual disorder transition.
• Neutron diffraction provided evidence for independent ordering of anion and cation sublattices.
• XAS measurements revealed a gradual increase in the effective coordination number of Zr from ~6 to ~7 across the series.

Conclusions:

• The order-disorder transition in Gd(2-x)Tb(x)Zr2O7 is confirmed to be gradual, contrary to initial XRD indications.
• Ordered domains persist throughout the defect fluorite region.
• The study highlights the importance of complementary techniques for accurately characterizing phase transitions in complex oxides.