Intricate disorder in defect fluorite/pyrochlore: a concord of chemistry and crystallography

David Simeone (1, 2) , Gordon James Thorogood (3, 4) , Da Huo (5) , Laurence Luneville (1, 6) , Gianguido Baldinozzi (1, 2) , Vaclav Petricek (7) , Florence Porcher (8) , Joel Ribis (1, 2) , Leo Mazerolles (9) , Ludovic Largeau (10) , Jean-François Bérar (11) , Suzy Surble (5)

1 SPMS - Laboratoire Structures, Propriétés et Modélisation des solides
2 SRMA - Service des Recherches Métallurgiques Appliquées
3 ANSTO - Australian Nuclear Science and Technology Organisation [Australie]
4 Nagaoka University of Technology
5 LEEL - UMR 3685 - Laboratoire d'Etudes des Eléments Légers
6 CEA-DES (ex-DEN) - CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire)
7 CAS - Czech Academy of Sciences [Prague]
8 LLB - UMR 12 - Laboratoire Léon Brillouin
9 ICMPE - Institut de Chimie et des Matériaux Paris-Est
10 C2N (UMR_9001) - Centre de Nanosciences et Nanotechnologies
11 NEEL - CRG - CRG & Grands instruments

Intuitively scientists accept that order can emerge from disorder and a significant amount of effort has been devoted over many years to demonstrate this. In metallic alloys and oxides, disorder at the atomic scale is the result of occupation at equivalent atomic positions by different atoms which leads to the material exhibiting a fully random or modulated scattering pattern. This arrangement has a substantial influence on the material's properties, for example ionic conductivity. However it is generally accepted that oxides, such as defect fluorite as used for nuclear waste immobilization matrices and fuel cells, are the result of disorder at the atomic scale. To investigate how order at the atomic scale induces disorder at a larger scale length, we have applied different techniques to study the atomic composition of a homogeneous La$^2$ Zr$^2$ O$^7$ pyrochlore, a textbook example of such a structure. Here we demonstrate that a pyrochlore, which is considered to be defect fluorite, is the result of intricate disorder due to a random distribution of fully ordered nano-domains. Our investigation provides new insight into the order disorder transformations in complex materials with regards to domain formation, resulting in a concord of chemistry with crystallography illustrating that order can induce disorder.

Domains: Chemical Sciences; Material chemistry

David Simeone, Gordon James Thorogood, Da Huo, Laurence Luneville, Gianguido Baldinozzi, et al.. Intricate disorder in defect fluorite/pyrochlore: a concord of chemistry and crystallography. Scientific Reports, 2017, 7, pp.3727. ⟨10.1038/s41598-017-02787-w⟩. ⟨cea-01541248⟩