Abstract
High-entropy oxides (HEOs) have attracted great interest in diverse fields because of their inherent opportunities to tailor and combine materials functionalities. The control of local order/disorder in the class is by extension a grand challenge toward realizing their vast potential. Here we report the first examples of pyrochlore HEOs with five M-site cations, for Nd2M2O7, in which the local structure has been investigated by neutron diffraction and pair distribution function (PDF) analysis. The average structure of the pyrochlores is found to be orthorhombic Imma, in agreement with radius-ratio rules governing the structural archetype. The computed PDFs from density functional theory relaxed special quasirandom structure models are compared with real space PDFs in this work to evaluate M-site order/disorder. Reverse Monte Carlo combined with ab initio molecular dynamics and Metropolis Monte Carlo simulations demonstrates that Nd2(Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2)2O7 is synthesized with its M-site local to nanoscale order highly randomized/disordered, while Nd2(Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2)2O7+x exhibits a strong distortion of the TiO6 octahedron and small degree of Ti chemical short-range order (SRO) on the subnanometer scale. Calculations suggest that this may be intrinsic, energetically favored SRO rather than due to sample processing. These results offer an important demonstration that the engineered variation of participating ions in HEOs, even among those with very similar radii, provides richly diverse opportunities to control local order/disorder motifs-and therefore materials properties for future designs. This work also hints at the exquisite level of detail that may be needed in computational and experimental data analysis to guide structure-property tuning in the emerging HEO materials class.
| Original language | English |
|---|---|
| Pages (from-to) | 4193-4204 |
| Number of pages | 12 |
| Journal | Journal of the American Chemical Society |
| Volume | 143 |
| Issue number | 11 |
| DOIs | |
| State | Published - Mar 24 2021 |
Funding
Material compositions evaluation, synthesis, and initial theory work were supported by the Laboratory Directed Research and Development (LDRD) Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. DOE. Work by V.R.C. and C.A.B., after 2020, was funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. Structure analysis was primarily supported by the Basic Energy Sciences Office of Science Early Career Award: Exploiting Small Signatures: Quantifying Nanoscale Structure and Behavior. STEM-EDS was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility (R.R.U.). The computing resources were made available through the VirtuES project as well as the Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. This research made use of the NOMAD instrument at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.
| Funders | Funder number |
|---|---|
| Basic Energy Sciences Office of Science | |
| Data Environment for Science | |
| U.S. DOE | |
| V.R.C. | |
| U.S. Department of Energy | |
| Office of Science | |
| Basic Energy Sciences | |
| Oak Ridge National Laboratory | |
| Laboratory Directed Research and Development | |
| Cades Foundation | DE-AC05-00OR22725 |
| Division of Materials Sciences and Engineering |