High Entropy Oxide: Local Disorder and Distortions

April 5, 2021
High Entropy Oxide
Nearest-neighbor functions nM−M(r) indicating the local short-range order of M-site cations in the RMC model of Nd2(Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2)2 O7 (inset display the positions of M-cations in a single RMC simulation). The dashed gray lines indicate the values expected for the case of average cation site distributions.

Scientific Achievement

The M site cations in pyrochlore high-entropy oxides (HEOs) of the form Nd2M2O7 are shown to be randomly distributed for M={Ta0.2Sc0.2Sn0.2Hf0.2Zr0.2}, but strong local TiO6 octahedron distortions and short-range order are observed for the slightly different case of M={Ti0.2Nb0.2Sn0.2Hf0.2Zr0.2}.

Significance and Impact

HEOs are of great interest in diverse fields because of the inherent opportunities to tailor and combine materials functionalities, where slight chemical variations lead to strikingly different local structures.

Research Details

  • The materials were characterized by electron microscopy, energy dispersive x-ray spectroscopy, and neutron total scattering.
  • The data were analyzed using pair distribution function analysis, Reverse Monte Carlo (RMC), and specialized density functional theory to elucidate the relationship between local and average structure. The level of detail needed to understand HEO materials is only possible using such multipronged approaches.

“Probing the Local Site Disorder and Distortion in Pyrochlore High-Entropy Oxides”

Bo Jiang, Craig A. Bridges, Raymond R. Unocic, Krishna Chaitanya Pitike, Valentino R. Cooper, Yuanpeng Zhang, De-Ye Lin, and Katharine Page

Journal of the American Chemical Society (2020).

DOI: https://dx.doi.org/10.1021/jacs.0c10739