Institut des Sciences Chimiques de Rennes, Université de Rennes 1, UMR CNRS-UR1 6226, Campus de Beaulieu, Bât 10B, 35042 Rennes Cedex, France.
Inorg Chem. 2012 Sep 17;51(18):9789-98. doi: 10.1021/ic301165a. Epub 2012 Sep 5.
We report a combined synchrotron X-ray and neutron diffraction study on as-grown La(2)CoO(4.14) single-crystal from 10 to 470 K. Unprecedented structural features in terms of a (3 + 2)D incommensurate modulation have been detected and characterized in the Low Temperature Orthorhombic (LTO) phase already at room temperature despite the complex twinning that was unravelled. A new intermediate phase between the LTO and High Temperature Tetragonal (HTT) phases has been observed for the first time (in the range of 413-433 K). The transformation from LTO to this so-called HTLO (High Temperature Less Orthorhombic) phase is associated to a lowering of orthorhombicity and a loss of one modulation vector, yielding a (3 + 1)D incommensurate modulation. Conversely, above 433 K the HTT phase appears as nonmodulated but exhibits a strong dynamic disorder of CoO(6) octahedra, which has been characterized in detail by reconstruction of nuclear densities via the Maximum Entropy Method (MEM).
我们报道了一个在 10 到 470 K 下生长的 La(2)CoO(4.14)单晶的同步加速器 X 射线和中子衍射联合研究。尽管已经解开了复杂的孪晶，但在室温下已经检测到并描述了低温正交相（LTO）中前所未有的（3 + 2）D 非共格调制的结构特征。首次观察到 LTO 和高温四方相（HTT）之间的新中间相（在 413-433 K 范围内）。从 LTO 到所谓的 HTLO（高温非正交相）的转变与正交度的降低和一个调制矢量的损失有关，导致（3 + 1）D 非共格调制。相反，高于 433 K 时，HTT 相表现为非调制，但表现出 CoO(6)八面体的强烈动态无序，这已经通过最大熵法（MEM）重建核密度进行了详细描述。
