An exhaustive symmetry approach to structure determination: phase transitions in Bi2Sn2O7
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The exploitable properties of many materials are intimately linked to symmetry-lowering structural phase transitions. We present an automated and exhaustive symmetry-mode method for systematically exploring and solving such structures which will be widely applicable to a range of functional materials. We exemplify the method with an investigation of the Bi2Sn2O7 pyrochlore, which has been shown to undergo transitions from a parent γ cubic phase to β and α structures on cooling. The results include the first reliable structural model for β-Bi2Sn2O7 (orthorhombic Aba2, a = 7.571833(8), b = 21.41262(2), and c = 15.132459(14) Å) and a much simpler description of α-Bi2Sn2O7 (monoclinic Cc, a = 13.15493(6), b = 7.54118(4), and c = 15.07672(7) Å, β = 125.0120(3)°) than has been presented previously. We use the symmetry-mode basis to describe the phase transition in terms of coupled rotations of the Bi2O′ anti-cristobalite framework, which allow Bi atoms to adopt low-symmetry coordination environments favored by lone-pair cations.
Lewis , J W , Payne , J L , Evans , I R , Stokes , H T , Campbell , B J & Evans , J S O 2016 , ' An exhaustive symmetry approach to structure determination: phase transitions in Bi2Sn2O7 ' Journal of the American Chemical Society , vol 138 , no. 25 , pp. 8031-8042 . DOI: 10.1021/jacs.6b04947
Journal of the American Chemical Society
Copyright © 2016 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
B.J.C. would like to acknowledge the US-UK Fulbright commission for a research fellowship and the University of Durham for hosting his research leave. J.W.L. would like to thank the EPSRC for a Ph.D. scholarship.
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