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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Superspace crystal symmetry of thermoelectric misfit cobalt oxides and predicted structural models
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Superspace crystal symmetry of thermoelectric misfit cobalt oxides and predicted structural models

机译:热电失配钴氧化物的超空间晶体对称性和预测的结构模型

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Single crystals of thermoelectric misfit lamellar cobalt oxide phases in the Bi-Ca-Co-O and I-Bi-Ca-Co-O systems were synthesized. They are characterized by aperiodic structures involving two partially independent sublattices: a CdI2-type pseudohexagonal CoO2 layer and a rocksalt-type BiCaO2 slab allowing the intercalation of iodine. The crystal symmetry of these structures is discussed using the four-dimensional superspace formalism. The superspace Lane classes of the iodine-free and the intercalated compounds are P2/m(0 delta 1/2) (a(1) = 4.901, b(1) = 4.730, b(2) = 2.80, c(1) = 14.66 angstrom, beta = 93.49 degrees) and A2/m(0 delta 1) (a(1)' = 4.903, b(1)' = 4.742, c(1)' = 36.51 angstrom, beta = 87.30 degrees), respectively. A comparison is given with the related Bi-SrCo-O misfit compounds. The present structures are compatible with the presence of an intrinsic modulation with a wavelength matching the misfit aperiodicity in the b direction. Preliminary partial structure refinements confirm the layer stacking of the structure and the intercalation of I between the Bi-O layers for the second phase. A comparison with other cobalt oxide phases, as well as symmetry and metric considerations allow us to predict average structures for these new phases and to describe the common structural features assumed for all these lamellar misfit cobalt oxides.
机译:合成了Bi-Ca-Co-O和I-Bi-Ca-Co-O-O体系中热电失配层状钴氧化物的单晶。它们的特征是包括两个部分独立的亚晶格的非周期性结构:CdI2型伪六方CoO2层和允许嵌入碘的岩盐型BiCaO2平板。这些结构的晶体对称性是使用四维超空间形式主义讨论的。无碘和插层化合物的超空间Lane类为P2 / m(0 delta 1/2)(a(1)= 4.901,b(1)= 4.730,b(2)= 2.80,c(1) = 14.66埃,贝塔= 93.49度)和A2 / m(0增量1)(a(1)'= 4.903,b(1)'= 4.742,c(1)'= 36.51埃,贝塔= 87.30度),分别。与相关的Bi-​​SrCo-O失配化合物进行了比较。本结构与固有调制的存在兼容,该固有调制的波长在b方向上与失配非周期性匹配。初步的部分结构改进证实了该结构的层堆叠以及第二阶段Bi-O层之间的I嵌入。与其他氧化钴相的比较以及对称性和度量标准的考虑,使我们能够预测这些新相的平均结构,并描述所有这些层状错配钴氧化物假定的常见结构特征。

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