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Title: Probing disorder in isometric pyrochlore and related complex oxides

Journal Article · · Nature Materials
DOI:https://doi.org/10.1038/nmat4581· OSTI ID:1334424
 [1];  [2];  [2];  [3];  [4];  [5];  [5];  [6];  [3];  [7]
  1. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Nuclear Engineering; Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division, Spallation Neutron Source (SNS)
  3. Stanford Univ., CA (United States). Dept. of Geological Sciences
  4. Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Earth and Environmental Sciences
  5. Forschungszentrum Julich (Germany). Inst. for Energy and Climate Research (IEK). Nuclear Waste Management and Reactor Safety
  6. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Physics and Astronomy
  7. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Nuclear Engineering
+ Show Author Affiliations

There has been an increased focus on understanding the energetics of structures that can accommodate unconventional ordering (e.g., disordered periodic arrays that appear at different length-scales). For example, the isometric pyrochlore structure, A2B2O7, forms a disordered, defect fluorite-structure, (A,B)4O7, or an aperiodic array, when exposed to extreme conditions]. The ability to accommodate disorder in its structure accounts for the tendency of some compositions to resist becoming aperiodic in high radiation fields or at high temperatures. Thus, these materials find application as host materials for immobilizing actinides, such as plutonium, fast ion conductors in solid oxide fuel cells, and thermal barrier coatings for gas turbine jet engines. Despite the importance of the disordering process, there has been only a limited understanding of the role of local ordering on the energetic landscape, mainly due to the use of techniques (i.e., X-ray/electron diffraction) that can only characterize the average structure over a large number unit cells and are insensitive to disorder on the oxygen sublattice. We have used neutron pair distribution functions (PDFs) to show that the disordered fluorite structure consists of a locally-ordered, orthorhombic structural unit that is repeated by a pseudo-translational symmetry, such that the ordered, orthorhombic and disordered, isometric arrays coexist at different length-scales. This disordering mechanism is a more general phenomenon in complex oxides, as PDF analysis has revealed that inversion in the isometric spinel structure, AB2O4 B(AB)O4, occurs by a similar process across the highly randomized B-site. This insight into order-disorder transformations induced intrinsically (chemical composition) or extrinsically (far from equilibrium conditions by high radiation fields) provides a new basis for understanding how modulated structures and correlated disorder at different length-scales affects the physical and transport properties of this important class of materials.

Research Organization:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
DOE Contract Number:
AC05-00OR22725; SC0001089
OSTI ID:
1334424
Journal Information:
Nature Materials, Vol. 15, Issue 5; ISSN 1476-1122
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English

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