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

Published version
Peer-reviewed

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Type

Article

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Authors

Childs, Christian 
Petitgirard, Sylvain 
Noked, Ori 

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.

Description

Keywords

34 Chemical Sciences, 3406 Physical Chemistry

Journal Title

Inorg Chem

Conference Name

Journal ISSN

0020-1669
1520-510X

Volume Title

57

Publisher

American Chemical Society (ACS)
Sponsorship
Royal Society (WM150023)
Engineering and Physical Sciences Research Council (EP/P022596/1)
Royal Society