Kishida Kyosuke, Goto Kengo, Inui Haruyuki
Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto, 606-8501, Japan.
Acta Crystallogr B. 2009 Aug;65(Pt 4):405-15. doi: 10.1107/S0108768109016243. Epub 2009 Jun 13.
It is shown that 21 ABX(3) perovskites with tilted BX(6) octahedra and layered ordering of A cations can be generated on the basis of group-subgroup relations. These structures (with 16 different space groups) are classified into ten diffraction types in terms of the conditions for superstructure reflections caused by the ordering of A cations, tilting of BX(6) octahedra and structural absences. SAED (selected-area electron diffraction) allows the distinction of seven of the 21 different perovskites, while additional symmetry analysis by CBED (convergent-beam electron diffraction) is needed for the remaining 14 structures. The space groups of lithium lanthanum titanate pseudomorphs (with discrete chemical compositions) are successfully deduced by electron diffraction experiments.
结果表明，基于群-子群关系可以生成21种具有倾斜BX(6)八面体和A阳离子层状有序排列的ABX(3)钙钛矿。根据由A阳离子有序排列、BX(6)八面体倾斜和结构消光引起的超结构反射条件，这些结构（具有16种不同的空间群）被分为十种衍射类型。选区电子衍射（SAED）能够区分这21种不同钙钛矿中的七种，而其余14种结构则需要通过会聚束电子衍射（CBED）进行额外的对称性分析。通过电子衍射实验成功推导出了具有离散化学成分的钛酸锂镧假晶的空间群。
