Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 143, Issue 11, Pages 4193-4204Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.0c10739
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Funding
- Laboratory Directed Research and Development (LDRD) Program of Oak Ridge National Laboratory
- U.S. DOE
- Basic Energy Sciences Office of Science Early Career Award: Exploiting Small Signatures: Quantifying Nanoscale Structure and Behavior
- Office of Science of the U.S. Department of Energy [DE-AC05-00OR22725]
- U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division
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High-entropy oxides (HEOs) are of great interest in various fields due to their potential in tailoring and combining materials functionalities. This study reports the investigation of local structures of pyrochlore HEOs with five M-site cations, revealing different levels of randomness in the M-site order. Computational and experimental analysis in this work provides insights into the control of local order/disorder motifs in HEOs for future material designs.
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 Nd-2(Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2)(2)O-7 is synthesized with its M-site local to nanoscale order highly randomized/disordered, while Nd-2(Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2)(2)O7+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.
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