Jones Daniel M
School of Physics, The University of Western Australia, Crawley 6009, Australia.
Acta Crystallogr B. 2007 Feb;63(Pt 1):69-74. doi: 10.1107/S0108768106045381. Epub 2007 Jan 15.
Convergent-beam electron diffraction (CBED) patterns tilted away from major zone axes have been used to re-examine the space groups of LaAlO3 and GdAlO3 perovskites. The higher-order Laue zones (HOLZ) in CBED patterns at such tilted orientations have been found to have high sensitivity to the presence of mirror symmetry. This sensitivity has enabled the space group of LaAlO3, previously claimed to be cubic (Fm3c), to be confirmed as rhombohedral R3c by CBED. It is clear that patterns of sufficient tilt will be more sensitive for distinguishing between screw axes and glide planes than the observation of HOLZ deficit lines in zero-order Laue zone reflections. No symmetry degrading effects due to the influence of tilted crystal surfaces could be observed.
倾斜于主要晶带轴的会聚束电子衍射（CBED）图案已被用于重新研究钙钛矿LaAlO₃和GdAlO₃的空间群。发现在这种倾斜取向的CBED图案中的高阶劳厄区（HOLZ）对镜面反射对称性的存在具有高灵敏度。这种灵敏度使得先前声称是立方晶系（Fm3c）的LaAlO₃的空间群通过CBED被确认为菱面体R3c。显然，与在零阶劳厄区反射中观察HOLZ缺失线相比，足够倾斜的图案对于区分螺旋轴和滑移面更敏感。未观察到由于倾斜晶体表面的影响而产生的对称性降低效应。
