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Title: Nature of the chemical bond and prediction of radiation tolerance in pyrochlore and defect fluorite compounds

Abstract

The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation-anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature. - Graphical abstract: Three-dimensional representation of the predicted critical amorphization temperature in pyrochlores.

Authors:
 [1];  [2];  [1];  [1];  [3];  [1];  [1];  [4];  [5]
  1. Cambridge Centre for Ceramic Immobilisation, Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ (United Kingdom)
  2. (Australia), E-mail: grl@ansto.gov.au
  3. Institute of Materials and Engineering Science, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234 (Australia)
  4. (United Kingdom)
  5. Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)
Publication Date:
OSTI Identifier:
21015802
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 180; Journal Issue: 4; Other Information: DOI: 10.1016/j.jssc.2007.01.028; PII: S0022-4596(07)00061-8; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATIONS; CHEMICAL BONDS; CRITICAL TEMPERATURE; CRYSTAL DEFECTS; FLUORITE; IRRADIATION; LATTICE PARAMETERS; PYROCHLORE; RADIATION EFFECTS

Citation Formats

Lumpkin, Gregory R., Institute of Materials and Engineering Science, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234, Pruneda, Miguel, Rios, Susana, Smith, Katherine L., Trachenko, Kostya, Whittle, Karl R., Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, and Zaluzec, Nestor J.. Nature of the chemical bond and prediction of radiation tolerance in pyrochlore and defect fluorite compounds. United States: N. p., 2007. Web. doi:10.1016/j.jssc.2007.01.028.
Lumpkin, Gregory R., Institute of Materials and Engineering Science, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234, Pruneda, Miguel, Rios, Susana, Smith, Katherine L., Trachenko, Kostya, Whittle, Karl R., Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, & Zaluzec, Nestor J.. Nature of the chemical bond and prediction of radiation tolerance in pyrochlore and defect fluorite compounds. United States. doi:10.1016/j.jssc.2007.01.028.
Lumpkin, Gregory R., Institute of Materials and Engineering Science, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234, Pruneda, Miguel, Rios, Susana, Smith, Katherine L., Trachenko, Kostya, Whittle, Karl R., Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, and Zaluzec, Nestor J.. Sun . "Nature of the chemical bond and prediction of radiation tolerance in pyrochlore and defect fluorite compounds". United States. doi:10.1016/j.jssc.2007.01.028.
@article{osti_21015802,
title = {Nature of the chemical bond and prediction of radiation tolerance in pyrochlore and defect fluorite compounds},
author = {Lumpkin, Gregory R. and Institute of Materials and Engineering Science, Australian Nuclear Science and Technology Organisation, Private Mail Bag 1, Menai, NSW 2234 and Pruneda, Miguel and Rios, Susana and Smith, Katherine L. and Trachenko, Kostya and Whittle, Karl R. and Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD and Zaluzec, Nestor J.},
abstractNote = {The radiation tolerance of synthetic pyrochlore and defect fluorite compounds has been studied using ion irradiation. We show that the results can be quantified in terms of the critical temperature for amorphization, structural parameters, classical Pauling electronegativity difference, and disorder energies. Our results demonstrate that radiation tolerance is correlated with a change in the structure from pyrochlore to defect fluorite, a smaller unit cell dimension, and lower cation-anion disorder energy. Radiation tolerance is promoted by an increase in the Pauling cation-anion electronegativity difference or, in other words, an increase in the ionicity of the chemical bonds. A further analysis of the data indicates that, of the two possible cation sites in ideal pyrochlore, the smaller B-site cation appears to play the major role in bonding. This result is supported by ab initio calculations of the structure and bonding, showing a correlation between the Mulliken overlap populations of the B-site cation and the critical temperature. - Graphical abstract: Three-dimensional representation of the predicted critical amorphization temperature in pyrochlores.},
doi = {10.1016/j.jssc.2007.01.028},
journal = {Journal of Solid State Chemistry},
number = 4,
volume = 180,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • The relationship between the ordering characteristic of the pyrochlore structure type and that characteristic of the ''defect fluorite'' structure type (immediately on either side of two phase regions separating the two structure types) in a range of rare earth sesquioxide-stabilized cubic zirconias was investigated by electron diffraction and imaging. Systematic structural change as a function of composition and relative size of the constituent metal ions is highlighted, and a multi-q to single-q = {1/2} [111]* model is proposed for the observed pyrochlore-to-defect fluorite phase transition. Strain introduced into the close-packed {l_brace}111{r_brace} metal ion planes of the defect fluorite average structuremore » by the local cation and oxygen vacancy distribution is pointed to as the likely origin of the observed behavior.« less
  • A careful investigation of the previously reported single phase, pyrochlore structure type Y{sub 2}(Zr{sub y}Ti{sub 1-y}){sub 2}O{sub 7}, 0=<y=<0.9 (YZT) solid solution has been carried out. Given the known slow rate of diffusion of cations in fluorite-related stabilized zirconia systems and the consequent difficulty in achieving equilibrium, careful attention was paid to synthesis procedures while Guinier XRD and electron diffraction were used to investigate the synthesized materials. As a consequence, a subtle but nonetheless clear two-phase region separating a pyrochlore-type solid solution field (from 0=<y=<3{approx}0.54) from a 'defect fluorite' type solid solution field (from {approx}0.68=<y=<1) has been found. The underlyingmore » crystal chemistry of the system has been investigated using the bond valence sum approach. The dielectric properties have also been measured as a function of composition. The dielectric constant and dielectric loss of the lowest y compounds are potentially quite useful but deteriorate rapidly with increasing Zr content.« less
  • A structural transition in rare earth pyrohafnates, Ln{sub 2}Hf{sub 2}O{sub 7} (Ln=Y, La, Pr, Nd, Tb, Dy, Yb and Lu), has been identified. Neutron diffraction showed that the structure transforms from well-ordered pyrochloric to fully fluoritic through the lanthanide series from La to Lu with a corresponding increase in the position parameter x of the 48f (Fd3{sup Macron }m) oxygen site from 0.330 to 0.375. As evidenced by the selected area electron diffraction, La{sub 2}Hf{sub 2}O{sub 7}, Pr{sub 2}Hf{sub 2}O{sub 7} and Nd{sub 2}Hf{sub 2}O{sub 7} exhibited a well-ordered pyrocholoric structure with the presence of intense superlattice spots, which becamemore » weak and diffuse (in Dy{sub 2}Hf{sub 2}O{sub 7} and Tb{sub 2}Hf{sub 2}O{sub 7}) before disappearing completely as the series progressed towards the Lu end. High resolution electron microscopic studies showed the breakdown of the pyrochlore ordering in the form of antiphase domains resulting in diffused smoke-like superlattice spots in the case of Dy{sub 2}Hf{sub 2}O{sub 7} and Tb{sub 2}Hf{sub 2}O{sub 7}. - Graphical abstract: Transmission electron microscopic studies showed the ordered pyrochlore to defect fluorite transition in rare-earth pyrohafnates to occur via the formation of anti-phase domains to start with. Highlights: Black-Right-Pointing-Pointer Pyrochlore to fluorite structural transition in rare earth pyrohafnates. Black-Right-Pointing-Pointer La{sub 2}Hf{sub 2}O{sub 7}, Pr{sub 2}Hf{sub 2}O{sub 7} and Nd{sub 2}Hf{sub 2}O{sub 7} showed well ordered pyrochlore structure. Black-Right-Pointing-Pointer Short range ordering in Dy{sub 2}Hf{sub 2}O{sub 7} and Tb{sub 2}Hf{sub 2}O{sub 7}. Black-Right-Pointing-Pointer Break down of pyrochlore ordering due to antiphase boundaries. Black-Right-Pointing-Pointer Rest of the series showed fluoritic structure.« less
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