Crystal structure of Pb2V3O9: Rietveld refinement and electron lone-pair localization. The magnetic susceptibility of Sr2+-substituted phases
Crystal structure of Pb2V3O9: Rietveld refinement and electron lone-pair localization. The magnetic susceptibility of Sr2+-substituted phases
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Pb2V3O9 的晶体结构：Rietveld 精修和电子孤对定位。
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
H. Steinfink
中科院分区：
文献类型：
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作者：
O. Mentré;A. Dhaussy;F. Abraham;E. Suard;H. Steinfink
收集 Pb{sub 2}V{sub 3}O{sub 9} 的粉末中子和 X 射线衍射数据并用于结构细化。报告了中子数据的三斜晶格参数。选择非标准晶胞是为了与 Sr{sub 2}V{sub 3}O{sub 9} 的单斜结构进行比较，其几乎是同构的。 PB{sup 2+}的6s{sup 2}电子导致对称性降低并扭曲Sr{sub 2}V{sub 3}P{sub 9}中V-O骨架中存在的氧钒键的协同排列。两个晶体学独立的 Pb{sup 2+} 之一处于由七个带有 Pb-O 键的氧原子形成的扭曲、封端的八面体环境中。另一个 Pb{sup 2+} 被九个氧原子包围，与 Pb-O 形成扭曲的三顶三棱柱。孤对 6s{sup 2} 电子已定位，距原子核约 0.58 {埃}。在四个晶体学独立的钒原子中，两个处于四面体配位，平均氧化数+5。另外两个为八面体配位，氧化数为+4。八面体通过角共享连接成平行于[101]的无限链。四面体与八面体共享角，形成二维片，然后通过铅离子连接成三维结构。一个八面体 V{sup 4+} 阳离子显示出从其多面体中心向八面体链中共享角的氧的位移，产生短氧钒键 1.67(4) {埃} 和长键 2.18(4) {埃}。铅和钒酸锶骨架之间的主要区别在于第二个 V{sup 4+} 离子向与四面体共享角的氧移动。这里，短键长为 1.72(8) {埃}，而相对顶点的短键长为 2.21(7) {埃}。因此，Sr{sub 2}V{sub 3}O{sub 9}链中V{双{下划线}键}O键的协同位移被三斜转变破坏，导致更无序的V{sup 4+}排列。这是观察到Pb{sup 2+} 和Sr{sup 2+} 相磁化率差异的主要原因。交替 J{sub 1} - J{sub 2} 链模型对于 Pb{sub 2}V{sub 3}O{sub 9} 的拟合效果令人满意，而常规链模型则与 Sr{sub 2}V{sub 3}O{sub 9} 的数据匹配。« less
Powder neutron and X-ray diffraction data from Pb{sub 2}V{sub 3}O{sub 9} were collected and used for structure refinement. The triclinic lattice parameters from neutron data are reported. The nonstandard unit cell was chosen for comparison with the monoclinic structure of Sr{sub 2}V{sub 3}O{sub 9} with which it is nearly isostructural. The 6s{sup 2} electrons of PB{sup 2+} cause the lowering of the symmetry and distort the cooperative arrangement of the vanadyl bonds existing in the V-O framework of Sr{sub 2}V{sub 3}P{sub 9}. One of the two crystallographically independent Pb{sup 2+} is in a distorted, capped, octahedral environment formed by seven oxygen atoms with Pb-O bonds. The other Pb{sup 2+} is surrounded by nine oxygen atoms that form a distorted, tricapped, trigonal prism with Pb-O. The lone-pair 6s{sup 2} electrons were located and are about 0.58 {angstrom} from the nucleus. Of the four crystallographically independent vanadium atoms, two are in tetrahedral coordination with a mean oxidation number +5. The other two are in octahedral coordination with oxidation number +4. The octahedra link by corner sharing into an infinite chain parallel to [101]. The tetrahedra share corners with the octahedra to form two-dimensional sheets that are then joined by the Pb ionsmore » into a three-dimensional structure. One octahedral V{sup 4+} cation shows displacement from its polyhedral center toward an oxygen that is corner-shared in the octahedral chain, giving rise to a short vanadyl bond, 1.67(4) {angstrom}, and a long bond of 2.18(4) {angstrom}. The main difference between the lead and strontium vanadate framework is in the displacement of the second V{sup 4+} ion toward an oxygen that is corner-shared with a tetrahedron. Here the short bond length is 1.72(8) {angstrom} while it is 2.21(7) {angstrom} to the opposite apex. Thus, the cooperative displacement of the V{double{underscore}bond}O bond in the Sr{sub 2}V{sub 3}O{sub 9} chains is broken by the triclinic transformation, leading to a more disordered V{sup 4+} arrangement. This is the main reason for the observed differences in the magnetic susceptibilities of the Pb{sup 2+} and Sr{sup 2+} phases. An alternating J{sub 1} - J{sub 2} chain model was satisfactorily fitted for Pb{sub 2}V{sub 3}O{sub 9} while a regular chain model matched the data for Sr{sub 2}V{sub 3}O{sub 9}.« less