Abstract
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 La2Zr2O7 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.
Highlights
To cite this version: David Simeone, Gordon James Thorogood, Da Huo, Laurence Luneville, Gianguido Baldinozzi, et al
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
If the samples are transforming from pyrochlore to defect fluorite with respect to grain size a change in local symmetry should be occurring
Summary
An aqueous solution of La(NO3)3 − 6(H2O) with a purity of 99.999% and ZrOCL2.8(H2O) with a purity of 99.5% (Aldrich products) were combined. Simulated neutron pair distribution function G(r) for the perfect and virtual crystals were computed (supplementary Fig. 4b) using realistic resolution functions from the Nanoscale Ordered materials and Diffraction at the Spallation Neutron Source beam line at Oak Ridge National Laboratory (Qmax = 3.1 nm−1). These calculations allow a direct comparison of our simulations with published experimental data and does not take into account the impact of nano domains on the distortion and the broadening of first peaks of G(r) as claimed for other pyrochlores[6, 22]
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