Mineralogisch-Petrographisches Institut, Universität Hamburg, 20146 Hamburg, Germany.
J Phys Condens Matter. 2011 Jan 26;23(3):035902. doi: 10.1088/0953-8984/23/3/035902. Epub 2011 Jan 5.
The structural evolution of PbSc(0.5)Nb(0.5)O(3) (PSN) under pressure has been studied by in situ powder neutron diffraction. Rietveld refinements to the data show that the continuous phase transition detected by x-ray diffraction at p(c) = 4.1 GPa (Maier et al 2010 Phys. Rev. B 81 174116) is associated with long-range ordering of antiphase octahedral tilts and local ordering of ferroic Pb displacements. Similar to PbSc(0.5)Ta(0.5)O(3) (PST) (Maier et al 2010 Acta Crystallogr. 66 280-91), antiphase octahedral tilting even exists below the critical pressure in a regime in which the structure retains a cubic metric. In contrast to PST, in which the Pb atomic displacement parameters (DPs) form ellipsoids elongated along the cubic {111} directions, the atomic DPs of Pb in PSN form flattened discs parallel to the cubic {111}-planes. This indicates that in PST the Pb displacements are along the cubic {111} directions, whereas in PSN the local Pb displacements are randomly distributed along the cubic {110} directions. The latter can be explained by the abundance of underbonded oxygen atoms associated with the chemical B-site disorder.
通过原位粉末中子衍射研究了 PbSc(0.5)Nb(0.5)O(3) (PSN) 在压力下的结构演变。对数据的 Rietveld 精修表明，在 p(c) = 4.1 GPa 时通过 x 射线衍射检测到的连续相变（Maier 等人，2010 年，Phys. Rev. B 81，174116）与反相八面体倾斜的长程有序和铁电 Pb 位移的局部有序有关。类似于 PbSc(0.5)Ta(0.5)O(3) (PST)（Maier 等人，2010 年，Acta Crystallogr. 66，280-91），即使在结构保留立方度量的临界压力以下的区域中，反相八面体倾斜也存在。与 PST 不同，在 PST 中，Pb 原子位移参数 (DP) 形成沿立方 {111} 方向拉长的椭球，而 PSN 中 Pb 的原子 DP 形成平行于立方 {111} 平面的扁平圆盘。这表明在 PST 中，Pb 位移沿立方 {111} 方向，而在 PSN 中，局部 Pb 位移沿立方 {110} 方向随机分布。后者可以通过与化学 B 位无序相关的缺电子氧原子的丰富来解释。
