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14 citations found for barrier, n

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Acta Cryst. (2019). A75, e204
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Neodymium molybdenum oxide, NdMo7.7O14, crystallizes in the orthorhombic space group Aba2. Its crystal structure derives from the NdMo8O14 type which contains bicapped octahedral Mo8 clusters. Because of the non-stoichiometry on the capping Mo sites and the absence of satellite reflections, Mo6, Mo7 and Mo8 clusters are expected to co-exist randomly.

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The solid-state compound Sn4.4Mo24O38 is the first reduced molybdenum oxide in which infinite oxygen-molybdenum chains based on two different trans-edge-shared Mo6 octahedral clusters, i.e. dioctahedral Mo10 and trioctahedral Mo14 clusters, are present. The Sn2+ cations statistically occupy channels delimited by the Mo-O chains.

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The title compound is isomorphous with the La and Pr members of the Ln3MoO7 series. However, a splitting of one of the lanthanide sites into two positions is observed in Sm3MoO7.

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Praseodymium molybdenum oxide, PrMo7.6O14, is isostructural with LaMo7.7O14 and NdMo7.7O14. Their crystal structures derive from the NdMo8O14 type, which contains cis-edge-sharing bi-face-capped octahedral Mo8 clusters. Because of the non-stoichiometry on the capping Mo sites and the absence of satellite reflections, Mo6, Mo7 and Mo8 clusters are believed to co-exist randomly.

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Tripraseodymium molybdenum heptaoxide, Pr3MoO7, is isostructural with La3MoO7. Its crystal structure consists of chains of corner-linked MoO6 octahedra that are parallel with the b axis and separated from each other by seven-coordinate Pr-O polyhedra.

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The title compound, praeseodymium hexamolybdenum dodecaoxide, PrMo6O12, crystallizes in the tetragonal space group I4/m and is isostructural with NdMo6O12. Both compounds adopt a hollandite-related structure with a tripled c axis compared to the mineral hollandite. Within the double chains of edge-sharing MoO6 octahedra, the Mo atoms form infinite chains of Mo3 triangular clusters. Another dominant feature of the structure is the ordering of the Pr3+ cations within the square-shaped channels delimited by the Mo-O double strings.

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Acta Cryst A. (2013). A69, s103-s104
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Acta Cryst. (2014). A70, C1194
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Can we solve aperiodic structures using intensities from electron diffraction? Yes! How? No mystery about it: the data analysis and the tools used for structure solution are essentially the same as the ones used in X-ray crystallography. The trick actually lies in new approaches used in electron crystallography. In analogy to X-ray diffraction, the so-called Electron Diffraction Tomography (EDT) [1] corresponds to a phi-scan data collection on a single crystal. There lies one major advantage of this technique: a powder sample is easily converted to infinitely large number of single crystals for electron diffraction. In case of aperiodic crystals this makes the difference over X-ray or neutron powder diffraction where, often, the lack of peaks clearly assignable to satellite reflections prevents any indexation and further analysis of the structure [2]. EDT allows for an accurate estimation of the modulation vector and a good guess of the super space group. These informations can be advantageously used as an input for X-ray or neutron powder diffraction. Not limited to indexation, EDT combined with Precession Electron Diffraction (PED) [3], offers a unique tool for solving modulated structures when crystals suitable for X-ray diffraction are missing. By limiting the paths for multiple scattering, PED makes the diffracted intensities closer to kinematical approximation so that they can be used efficiently for structure solution. Regarding aperiodic crystals, the superspace electron density map, generated as an output of the charge flipping algorithm used in Superflip, can be interpreted to obtain a structural model. This will be illustrated on a series of layered materials closely related to the Aurivillius phases belonging to the pseudo-binary Bi5Nb3O15-ABi2Nb2O9 (A=Pb, Sr, Ca, Ba). Limitations and possible combination with powder diffraction patterns will be discussed.


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Acta Cryst. (2005). A61, c396
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Acta Cryst. (2007). A63, s94-s95
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Acta Cryst. (2018). A74, e326
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An X-ray transparent electrochemical cell with dense glassy carbon windows (Sigradur-G) for operando bench-top X-ray diffraction in reflection geometry is demonstrated.

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