Local ordering in disordered NdxZr1-xO2-0.5x pyrochlore as observed using neutron total scattering

• Published in: Acta materialia 2022-02, Vol.225, Article 117590
• Main Authors: Drey, Devon, O'Quinn, Eric, Finkeldei, Sarah, Neuefeind, Joerg, Lang, Maik
• Format: Article
• Language: English
• Subjects: Lanthanide-doped zirconia; Neutron diffraction; Order to disorder phase transformations; Pair correlation function; Short-range ordering
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2021.117590

Pyrochlore complex oxides (A2B2O7) are an important class of fluorite-derivative ceramics with exceptional chemical and structural versatility which make them ideal model systems for studying disordering mechanisms over a range of spatial scales. Neutron total scattering methods were used to analyze the structural behavior in the non-stoichiometric series NdxZr1-xO2-0.5x (0.5 ≤ x ≤ 0.23) as a function of Nd content, x. Characterization of the structure functions using Rietveld refinement and the pair distribution functions with small-box refinement reveal complex disordering pathways; the average, long-range phase changes over a very narrow compositional range from pyrochlore (Fd3¯m) to defect fluorite (Fm3¯m) through full randomization of the cation and anion sublattices at x ∼ 0.31, while the local, short-range structure continuously adopts a weberite-type atomic arrangement (C2221). Comparison to a previously studied Ho2Ti2-xZrxO7 solid solution series reveals how changes in chemical composition and stoichiometry modify defect formation and determine how disordering progresses across different length scales in pyrochlore oxides. [Display omitted]