Title: Covalency is Frustrating: La₂Sn₂O₇ and the Nature of Bonding in Pyrochlores under High Pressure–Temperature Conditions

Abstract

Natural specimens of the pyrochlore (A₂B₂O₇) compounds have been found to retain foreign actinide impurities within their parent framework, undergoing metamictization to a fully amorphous state. The response to radionuclide decay identifies pyrochlore systems with having high radiation tolerance and tailored use in radioactive waste applications and radionuclide sequestration. High pressure is a powerful pathway to high density states and amorphization with parallels to radiation-induced processes. Here, La₂Sn₂O₇ is evaluated under extreme conditions via the combination of laser heating in a diamond anvil cell with X-ray diffraction and Raman spectroscopy. The measurements are supported by ab initio random structure searching and molecular dynamics calculations. A new ground state at 70 GPa is revealed, and high temperature annealing is fundamental to access its crystalline ground state and fully determine the structure. This crystalline phase (P2₁/c) retains its structural integrity during decompression and is fully recoverable to ambient conditions. The final state of the system is shown to be highly pathway dependent due to the covalent nature of the Sn-O bonding. The Tc pyrochlore, La₂Tc₂O₇, is analyzed for similarities in the bonding to determine the likelihood of an analogous pathway dependency to a final state

Authors:

Childs, Christian ^[1]; Lawler, Keith V.  ^[2];

• Search DOE PAGES for author "Lawler, Keith V."
• Search DOE PAGES for ORCID "0000-0003-1087-5815"

Hector, Andrew L.  ^[3];

• Search DOE PAGES for author "Hector, Andrew L."
• Search DOE PAGES for ORCID "0000-0002-9964-2163"

Petitgirard, Sylvain ^[4]; Noked, Ori ^[5]; Smith, Jesse S. ^[6]; Daisenberger, Dominik ^[7]; Bezacier, Lucile ^[8]; Jura, Marek ^[9]; Pickard, Chris J. ^[10]; Salamat, Ashkan ^[1]

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+ Show Author Affiliations

1. Department of Physics and Astronomy and HiPSEC, University of Nevada Las Vegas, Las Vegas, Nevada 89154, United States
2. Department of Chemistry and Biochemistry and HiPSEC, University of Nevada Las Vegas, Las Vegas, Nevada 89154, United States
3. Department of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom
4. Bayerisches GeoInstitut (BGI), University of Bayreuth, 95444 Bayreuth, Germany
5. Lyman Laboratory of Physics, Harvard University, Cambridge, Massachusetts 02138, United States
6. High Pressure Collaborating Access Team at Advanced Photon Source, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, Illinois 60439, United States
7. Diamond Light Source Ltd., Didcot, Oxfordshire OX11 0DE, United Kingdom
8. European Synchrotron Radiation Facility, BP 220, 38043 Grenoble, Cedex 9, France
9. ISIS, STFC, Harwell Innovation Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom
10. Department of Materials Science &, Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

Publication Date:

Mon Jul 02 00:00:00 EDT 2018

Research Org.:

Univ. of Nevada, Las Vegas, NV (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES); Engineering and Physical Sciences Research Council (EPSRC)

OSTI Identifier:

1461560

Alternate Identifier(s):

OSTI ID: 1508588; OSTI ID: 1771008

Grant/Contract Number:  

NA0001982; NA0001974; FG02-99ER45775; AC02-06CH11357; EP/P022596/1

Resource Type:

Published Article

Journal Name:

Inorganic Chemistry

Additional Journal Information:

Journal Name: Inorganic Chemistry Journal Volume: 57 Journal Issue: 24; Journal ID: ISSN 0020-1669

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE