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Pyrochlore to Fluorite Transitions – Ordering in Fluorites?

Published online by Cambridge University Press:  20 February 2017

Karl R. Whittle,
Lachlan M. Cranswick,
Simon A.T. Redfern,
Ian P. Swainson and
Gregory R. Lumpkin
Karl R. Whittle
Affiliation:
Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB1, Menai, NSW 2234, AustraliaDepartment of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
Lachlan M. Cranswick
Affiliation:
Canadian Neutron Beam Centre, Chalk River National Laboratories, Ontario, Canada
Simon A.T. Redfern
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, United Kingdom
Ian P. Swainson
Affiliation:
Canadian Neutron Beam Centre, Chalk River National Laboratories, Ontario, Canada
Gregory R. Lumpkin
Affiliation:
Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB1, Menai, NSW 2234, Australia
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Abstract

Two systems have been studied La2-xYxZr2O7 and La2-xYxHf2O7, as part of an on-going study of radiation tolerance in nuclear waste forms and related oxide materials. The structural effects of increasing Y content in La based zirconate and hafnate pyrochlores have been studied with neutron diffraction and electron microscopy. Results have shown a difference in structural stability for both the pyrochlore and fluorite phases within each system, including the presence of two-phase regions in both systems. In the zirconate, the two-phase region lies in the range x = 0.9-1.6. This is shifted to higher Y content in the hafnate system and lies in the range of x = 1.5 to approximately 1.8-1.9. In addition to the differences in phase stability, electron diffraction, predominantly down the [110] zone axis, has shown evidence for ordering in the form of structured diffuse scattering within the fluorite phases.

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