Friday, April 16, 2010

Journal of Physical Chemistry B and C, Vol. 114, Issues 14 and 15

7Li NMR Knight Shifts in Li−Sn Compounds: MAS NMR Measurements and Correlation with DFT Calculations

Emilie Bekaert†, Florent Robert‡, Pierre Emmanuel Lippens‡ and Michel Mntrier*†

J. Phys. Chem. C, 2010, 114 (14), pp 6749–6754
DOI: 10.1021/jp100365u

Abstract: Several Li−Sn crystalline phases, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2, and Li22Sn5, were prepared by ball-milling and studied by 7Li MAS NMR spectroscopy with silica as a diluting agent to avoid field penetration limitations. All phases except for LiSn exhibit exchanged NMR signals at room temperature for the various types of Li present in the unit cells, in the 10 to 100 ppm range. Electronic structure calculations based on first-principles method led to a rather good correlation between the participation of the Li 2s orbital to the density of states (DOS) at the Fermi level and the corresponding NMR Knight shift for the two Li crystallographic types in the case of LiSn, and for the weighted average of the different crystallographic types in the case of the NMR-exchanged signals for the other compounds.

A Novel Phase Transformation Phenomenon in Mesostructured Aluminophosphate

Wanling Shen†, Shenhui Li†, Jun Xu†, Hailu Zhang†, Wei Hu†, Dan Zhou‡, Jianan Zhang‡, Jihong Yu‡, Wujun Xu§, Yao Xu§ and Feng Deng*†

J. Phys. Chem. C, 2010, 114 (15), pp 7076–7084
DOI: 10.1021/jp911959u

Abstract: A novel phase transformation phenomenon that involves two successive phase transformation events was found for the first time in the synthesis of mesostructured aluminophosphate and studied by XRD, TEM, and multinuclear solid-state NMR techniques. The results showed that a hexagonal phase Hex and two lamellar phases, L1 and L2, were formed after hydrothermal treatment for 1, 3, and 50 h, respectively. The status of the surfactant was found to be arrayed interdigitated in a bilayer with a tilt angle in L1 phase but upright in L2 phase. A mechanism that the exciting of the alkane tail of the surfactant together with the condensation of aluminophosphate cooperatively promoted the phase transformation was proposed for the observed phenomenon. Additionally, a ZON microporous structure was found for the first time existing in the framework of the mesostructured aluminophosphate.

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