Department of Chemistry, University Science Site, Durham University , South Road, Durham DH1 3LE, United Kingdom.
Department of Physics & Astronomy, Brigham Young University , Provo, Utah 84602, United States.
J Am Chem Soc. 2016 Jun 29;138(25):8031-42. doi: 10.1021/jacs.6b04947. Epub 2016 Jun 15.
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.
许多材料的可利用性质与其对称性降低的结构相变密切相关。我们提出了一种自动化和详尽的对称模式方法，用于系统地探索和解决这些结构，该方法将广泛适用于一系列功能材料。我们以 Bi2Sn2O7 钙钛矿的研究为例，该材料已被证明在冷却过程中从母体 γ 立方相经历到 β 和 α 结构的转变。结果包括 β-Bi2Sn2O7（正交 Aba2，a = 7.571833(8)，b = 21.41262(2)，c = 15.132459(14) Å）的第一个可靠结构模型，以及对 α-Bi2Sn2O7（单斜 Cc，a = 13.15493(6)，b = 7.54118(4)，c = 15.07672(7) Å，β = 125.0120(3)°）的描述比以前更为简单。我们使用对称模式基来描述相变，即 Bi2O'反尖晶石骨架的耦合旋转，这允许 Bi 原子采用孤对阳离子有利于的低对称性配位环境。
