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首页> 外文期刊>International Journal of Quantum Chemistry >An electron diffraction and bond valence sum study of the space group symmetries and structures of the photocatalytic 1 : 2 B site ordered A(3)CoNb(2)O(9)perovskites (A = Ca2+, Sr2+, Ba2+)
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An electron diffraction and bond valence sum study of the space group symmetries and structures of the photocatalytic 1 : 2 B site ordered A(3)CoNb(2)O(9)perovskites (A = Ca2+, Sr2+, Ba2+)

机译：电子衍射和键价和研究光催化1：2 B位的有序A（3）CoNb（2）O（9）钙钛矿（A = Ca2 +，Sr2 +，Ba2 +）的空间群对称性和结构

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A careful investigation has been carried out into the space group symmetries, structures and crystal chemistries of the 1:2 B-site ordered triple perovskites A(3)Co(2+)Nb5/2(+)O(9) (A = Ca2+, Sr2+, Ba (2+)) using a combination of bond valence sum calculations, powder XRD and electron diffraction. A recent investigation of these compounds by Yin et al. reported a random distribution of Co2+ and Nb5+ ions onto the perovskite B-site positions and hence Pm3m (a = a(p), subscript p for parent perovskite sub-structure) space group symmetry for the A= Ba and Sr compounds and a monoclinically distorted variant thereof (although no space group was given) in the case of the A = Ca compound. An electron diffraction study, however, shows that the A = Ba compound occurs in a 1:2 B site ordered trigonal P3m1, a(h) = b(p) - c(p), b(h) = c(p) - a(p), c(h) = a(p) + b(p) + c(p) structure type while both the A = Ca and Sr compounds occur at room temperature in monoclinic P12(1) /cl, a(m) = [112](p), b(m) = [110](p), c(m) = 3 [110](p), perovski-related structure types. The latter monclinic structure type can be described as a modulated variant of the 1:2 B site ordered trigonal P3m1 structure type with the additional modulations associated with a b(-)b(-)c(+) octahedral tilt sequence. Bond valence sum calculations are used to explain why this should be so as well as to provide a useful zeroth-order approximation to the structures of each of the compounds. (C) 2004 Elsevier Inc. All rights reserved.
机译：仔细研究了空间组的对称性，结构和晶体化学的1：2 B站点有序三重钙钛矿A（3）Co（2+）Nb5 / 2（+）O（9）（A = Ca2 +，Sr2 +，Ba（2+））使用结合价和计算，粉末XRD和电子衍射的组合。 Yin等人最近对这些化合物的研究。报道了Co2 +和Nb5 +离子在钙钛矿B位上的随机分布，因此Pm3m（a = a（p），母钙钛矿亚结构的下标p）对A = Ba和Sr化合物的空间群对称性和单临床在A = Ca化合物的情况下，其变形形式（尽管未提供空间基团）。然而，电子衍射研究表明，A = Ba化合物以1：2 B位置出现在有序三角形P3m1中，a（h）= b（p）-c（p），b（h）= c（p） -a（p），c（h）= a（p）+ b（p）+ c（p）结构类型，而A = Ca和Sr化合物均在室温下在单斜晶P12（1）/ cl中出现（m）= [112]（p），b（m）= [110]（p），c（m）= 3 [110]（p），与钙钛矿有关的结构类型。后者的单斜结构类型可以描述为1：2 B位置有序三角P3m1结构类型的调制变体，具有与b（-）b（-）c（+）八面体倾斜序列相关的其他调制。结合价合计计算用于解释为什么应该如此，并为每种化合物的结构提供有用的零阶近似。 （C）2004 Elsevier Inc.保留所有权利。

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