| 1. |
- Lund, Kristina, et al.
(författare)
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Accidental extinction in powder XRD intensity of porous crystals : Mesoporous carbon crystal CMK-5 and layered zeolite-nanosheets
- 2010
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 128:03-jan, s. 71-77
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Tidskriftsartikel (refereegranskat)abstract
- CMK-5 mesoporous carbon crystals with p6mm symmetry and different carbon-wall thicknesses were prepared using furfuryl alcohol. We clearly observed that the XRD intensity of the 10 reflection diminishes at a certain thickness of carbon-wall, i.e., an ""accidental extinction"" happens in CMK-5. In order to make clear the condition of the ""accidental extinction"", XRD intensity is analytically formulated/calculated for two-dimensional system with p6mm symmetry. The conditions for the ""accidental extinction"" for the I I and 20 reflections as well as for the 10 reflection in CMK-5 were clarified. Pore diameter and carbon wall thickness were measured independently by N-2 gas adsorption isotherm and TEM images as a function of the carbon-loading, and we confirmed internal consistency between the observations and calculation for the ""accidental extinction"". Similarly it was pointed out through analytical formulation for one-dimensional system such as layered zeolite-nanosheets that the ""accidental extinction"" could be observed for the order (I > I) at the certain conditions. It was shown as a whole that knowledge of occurrence of the ""accidental extinction"" not only will prevent from determining false symmetry but also will provide internal structural information.
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| 2. |
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| 3. |
- Muroyama, Norihiro, et al.
(författare)
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Argon adsorption on MCM-41 mesoporous crystal studied by in situ synchrotron powder X-ray diffraction
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:29, s. 10803-10813
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Tidskriftsartikel (refereegranskat)abstract
- Equilibrium argon adsorption from the gas phase on mesoporous MCM-41 silica of hexagonal structure is directly studied by in situ synchrotron powder X-ray diffraction (XRD) measurements at SPring-8. The diffraction intensity data is analyzed by extending the previously developed analytical formula for the crystal structure factors of MCM-41 to account for argon adsorbed in the pores. It is clearly observed that argon adsorbs in layers on the pore walls at low gas pressures and exhibits sudden capillary condensation as the gas pressure increased. The proposed method of interpretation of XRD data allows one to calculate the density ratio between the silica wall and condensed argon, the pore size, and the pore wall fluctuation/roughness, together with the thickness of the adsorbed layer as a function of the gas pressure. The results of in situ XRD experiments are compared with the results of argon adsorption volumetric experiments. The adsorption data are interpreted with the quench solid density functional theory (QSDFT), which takes into account the pore wall roughness. The perfect agreement of the QSDFT isotherm predicted from the adsorption data and the XRD recalculated isotherm suggests that the adsorption porosimetry and XRD measurements can be reconciled provided a proper interpretation of the experimental data.
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| 4. |
- Muroyama, Norihiro, 1980-
(författare)
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Studies of inorganic crystal structures and gas adsorption process in mesoporous crystals : New approach through analysis of electron charge distribution by synchrotron powder X-ray diffraction
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Using synchrotron powder XRD experiments, I studied (i) structures of silica mesoporous MCM-41 and MCM-48 crystals, (ii) gas adsorption processes of Ar and N2 in the mesopores of the mesoporous crystals, and (iii) bonding features of CaAl2-xZnx crystals through the analysis of electron charge density distributions. In the case of mesoporous crystals, the following two different approaches were taken depending on the number of observed X-ray reflections1. The analytical expression was chosen and further developed to study the size and shape of the mesopores with the plane group of p6mm by powder XRD experiments. For MCM-41, following the determination of the mesopores’ size and shape, and the thickness of the adsorbed gas layer as a function of the gas pressure were successfully observed. In addition, for carbon pipe mesoporous crystals CMK-5, the carbon pipe thickness was determined and the diffraction pattern was discussed quantitatively focusing on the “accidental extinction.” 2. Maximum entropy method (MEM) was used for the structural study of MCM-48 (3D bicontinuous Ia-3d ) and for the gas adsorption process within the mesopores.By adopting the MEM approach, the study of “bonding electrons” and associated atomic displacements from the ideal Kagome net in the Laves phase CaAl2-xZnx were observed. In particular, the two Kagome nets in the C36 structure showed different feature in the electron density distributions between each other.
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| 5. |
- Söderberg, Karin, et al.
(författare)
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Electron charge distribution of CaAl2−xZnx : Maximum Entropy Method combined with Rietveld analysis of High-resolution-synchrotron X-ray powder diffraction data
- 2008
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 181:8, s. 1998-2005
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Tidskriftsartikel (refereegranskat)abstract
- Using short wavelength X-rays from synchrotron radiation (SPring-8), high-resolution powder diffraction patterns were collected. In order to study both the structural relationship and the mechanism of stability in the CaAl2−xZnx system, among the Laves phases (MgCu2 and MgNi2 type) and KHg2-type structures, the charge density distribution of CaAl2−xZnx as a function of x was obtained from the diffraction data by Rietveld analysis combined with the maximum entropy method (MEM). In the MEM charge density maps overlapping electron densities were clearly observed, especially in the Kagomé nets of the Laves phases. In order to clarify the charge redistribution in the system, the deformation charge densities from the densities formed by the constituent free atoms are discussed. In the ternary MgNi2-type phase, partial ordering of Al and Zn atoms is observed, a finding that is supported by ab-initio total energy calculations.
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| 6. |
- Zhang, Qing, et al.
(författare)
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Andersson-Magnéli Phases TinO2n-1 : Recent Progress Inspired by Swedish Scientists
- 2021
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Ingår i: Zeitschrift für Anorganische und Allgemeines Chemie. - : Wiley. - 0044-2313 .- 1521-3749. ; 647:2-3, s. 126-133
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Tidskriftsartikel (refereegranskat)abstract
- Among homologous series of metal oxides, Andersson-Magneli phases TinO2n-1 (n=4-10) have attracted renewed scientific attention because of their behaviour in electrical conductivity and chemical/thermal stability. Various applications have also been reported for the phases with different values of n, or slightly reduced rutile (TiO2). The characteristic properties of these materials depend strongly on the compositional deviation from TiO2 and the way in which the structure accommodates the deviation. Thus, an urgent requirement is to overcome difficulties in characterizing such materials at atomic resolution. Here, we trace the discovery of the Andersson-Magneli phases, and report the application of recent developments in electron microscopy to reveal the relation, at the local level, between structural characteristics and electronic states, specifically for the materials TinO2n-1 with n=4-8. The electrical conductivity of Ti4O7 has been reported previously to show three clearly distinct states on decreasing temperature from 300 K. For this reason, we focus on Ti4O7 as a representative example of the TinO2n-1 phases and report structural characteristics at temperatures corresponding to each of the three different phases, focusing on the distribution of Ti3+ and Ti4+ cations from analysis of single-crystal XRD data. Electron diffraction experiments and electrical conductivity measurements are also reported.
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