Oxide ion conductors require migration pathways for ions to pass through the lattice, typically via hopping through vacancy sites. The ease of this migration is dictated by both the bonding strength, and the structure (relative vacancy locations), with these characteristics guiding the ion conductivity and subsequently the minimum useful working temperature. The rare-earth oxides, with general formula A₂B₂O₇ (where A3+ is a rare-earth ion, and B4+ is a transition or p-block metal), have shown reasonable ion conductivity properties. These oxides show distinct structure types dependent on the A/B ion size ratio: rA/rB > 1.46 result in an ordered pyrochlore structure, and rA/rB < 1.46 results in a disordered defect-fluorite structure [1]. Probes of the ion local structure (spectroscopic methods), however, don’t show an abrupt change across this distinct structural-border [2]. Understanding the subtleties of the structural changes through this family is important for explaining the observed ion-conductivities [3]. In this short seminar I will show the results of our recent efforts to use a combination of neutron and X-ray diffraction, with small box pair-distribution-function analysis (xPDF and nPDF) to better understand the local structure evolution across the heavy rare-earth zirconates, A₂Zr₂O₇.

References

[1] J. Shamblin, M. Feygenson, J. Neuefeind, et al., Nat. Mater. 15, 507 (2016).

[2] P. E. R. Blanchard, R. Clements, B. J. Kennedy, et al., Inorg. Chem. 23, 41 (2012).

[3] M. Shafique, et al., J. Alloys Compd. 671, 226 (2016).