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Covalency is frustrating: La 2 Sn 2 O 7 and the nature of bonding in pyrochlores under high pressure-temperature conditions

DOI: 10.1021/acs.inorgchem.8b01419 DOI Help

Authors: Christian Childs (University of Nevada Las Vegas) , Keith V. Lawler (University of Nevada Las Vegas) , Andrew L. Hector (University of Southampton) , Sylvain Petitgirard (University of Bayreuth) , Ori Noked (Harvard University) , Jesse S. Smith (Carnegie Institution of Washington) , Dominik Daisenberger (Diamond Light Source) , Lucile Bezacier (European Synchrotron Radiation Facility) , Marek Jura (ISIS) , Chris J. Pickard (University of Cambridge; Tohoku University) , Ashkan Salamat (University of Nevada Las Vegas)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Inorganic Chemistry

State: Published (Approved)
Published: July 2018

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.

Subject Areas: Chemistry

Instruments: I15-Extreme Conditions

Other Facilities: European Synchrotron Radiation Facility; Advanced Photon Source