title: An Exhaustive Symmetry Approach to Structure Determination: Phase Transitions in Bi2Sn2O7.
abstract: 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.
authors.affiliation: Department of Chemistry, University Science Site, Durham University , South Road, Durham DH1 3LE, United Kingdom.
authors.forename: James W
authors.initials: JW
authors.lastname: Lewis
authors.affiliation: Department of Chemistry, University Science Site, Durham University , South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Julia L
authors.initials: JL
authors.lastname: Payne
authors.affiliation: Department of Chemistry, University Science Site, Durham University , South Road, Durham DH1 3LE, United Kingdom.
authors.forename: Ivana Radosavljevic
authors.initials: IR
authors.lastname: Evans
authors.affiliation: Department of Physics & Astronomy, Brigham Young University , Provo, Utah 84602, United States.
authors.forename: Harold T
authors.initials: HT
authors.lastname: Stokes
authors.affiliation: Department of Physics & Astronomy, Brigham Young University , Provo, Utah 84602, United States.
authors.forename: Branton J
authors.initials: BJ
authors.lastname: Campbell
authors.affiliation: Department of Chemistry, University Science Site, Durham University , South Road, Durham DH1 3LE, United Kingdom.
authors.forename: John S O
authors.initials: JS
authors.lastname: Evans