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Title: Distortion-stabilized ordered structures in A 2BB’O 7 mixed pyrochlores

Abstract

Pyrochlore oxides (A 2B 2O 7) are interesting for a number of technological applications, including radiation damage tolerance and as ionic conductors. Mixed pyrochlores—containing two A and/or two B site cations—provide even more flexibility for tailoring properties owing to the diverse chemical and configurational degrees of freedom accessible within this chemical space. Here, we examine relative stability of different cation orderings in one model double pyrochlore Gd 2(Zr xTi 1–x) 2O 7, as a function of Zr content x. Our results show that, in the presence of some very specific local cation arrangements, certain cation-ordered compositions in this system are highly stabilized as a result of large oxygen relaxation displacements, leading to the formation of an ordered ‘double’ pyrochlore structure. The origins of these anomalous oxygen relaxations are traced back to both the local cation symmetry and a strong chemical preference of Zr atoms towards adopting a 7-fold coordination environment, as opposed to a 6-fold coordination available in a regular pyrochlore structure. Subsequently, we examine the stability of this type of ordering in 131 other pyrochlore compositions. Here, the implications of our findings are discussed in relation to the observed composition-dependent ionic conductivity in these systems and connections with previouslymore » reported experimental findings are made.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Michigan, Ann Arbor, MI (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1542823
Report Number(s):
LA-UR-18-26270
Journal ID: ISSN 2057-3960
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
npj Computational Materials
Additional Journal Information:
Journal Volume: 5; Journal Issue: 1; Journal ID: ISSN 2057-3960
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English

Citation Formats

Pilania, Ghanshyam, Puchala, Brian, and Uberuaga, Blas P. Distortion-stabilized ordered structures in A2BB’O7 mixed pyrochlores. United States: N. p., 2019. Web. doi:10.1038/s41524-018-0144-1.
Pilania, Ghanshyam, Puchala, Brian, & Uberuaga, Blas P. Distortion-stabilized ordered structures in A2BB’O7 mixed pyrochlores. United States. doi:10.1038/s41524-018-0144-1.
Pilania, Ghanshyam, Puchala, Brian, and Uberuaga, Blas P. Mon . "Distortion-stabilized ordered structures in A2BB’O7 mixed pyrochlores". United States. doi:10.1038/s41524-018-0144-1. https://www.osti.gov/servlets/purl/1542823.
@article{osti_1542823,
title = {Distortion-stabilized ordered structures in A2BB’O7 mixed pyrochlores},
author = {Pilania, Ghanshyam and Puchala, Brian and Uberuaga, Blas P.},
abstractNote = {Pyrochlore oxides (A2B2O7) are interesting for a number of technological applications, including radiation damage tolerance and as ionic conductors. Mixed pyrochlores—containing two A and/or two B site cations—provide even more flexibility for tailoring properties owing to the diverse chemical and configurational degrees of freedom accessible within this chemical space. Here, we examine relative stability of different cation orderings in one model double pyrochlore Gd2(ZrxTi1–x)2O7, as a function of Zr content x. Our results show that, in the presence of some very specific local cation arrangements, certain cation-ordered compositions in this system are highly stabilized as a result of large oxygen relaxation displacements, leading to the formation of an ordered ‘double’ pyrochlore structure. The origins of these anomalous oxygen relaxations are traced back to both the local cation symmetry and a strong chemical preference of Zr atoms towards adopting a 7-fold coordination environment, as opposed to a 6-fold coordination available in a regular pyrochlore structure. Subsequently, we examine the stability of this type of ordering in 131 other pyrochlore compositions. Here, the implications of our findings are discussed in relation to the observed composition-dependent ionic conductivity in these systems and connections with previously reported experimental findings are made.},
doi = {10.1038/s41524-018-0144-1},
journal = {npj Computational Materials},
number = 1,
volume = 5,
place = {United States},
year = {2019},
month = {1}
}

Journal Article:
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Figures / Tables:

Fig. 1 Fig. 1: Calculated mixing energies (i.e., formation energies relative to the pure single pyrochlore end point compositions with x = 0 and x = 1) per primitive unit cell (with 22 atoms, containing two effective pyrochlore formula units) for the entire set of 704 unique configurations enumerated within the Gd2(ZrxTi1−x)2O7more » chemistries. The DFT predicted convex hull is represented as a solid line. The atomistic structures for the identified ground-state ordered structures on the convex hull are illustrated. While Gd and O atoms are represented by purple and red spheres, Ti and Zr polyhedra are depicted in blue and green colors, respectively« less

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