An Exhaustive Symmetry Approach to Structure Determination: Phase Transitions in Bi2Sn2O7

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• 作者：James W. Lewis ; Julia L. Payne ; Ivana Radosavljevic Evans ; Harold T. Stokes ; Branton J. Campbell ; John S. O. Evans
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：June 29, 2016
• 年：2016
• 卷：138
• 期：25
• 页码：8031-8042
• 全文大小：804K
• 年卷期：0
• ISSN：1520-5126

文摘

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.