Sodalite solid solution systems

Diese Arbeit über "Sodalite Solid Solution Systems" befasst sich mit der Synthese und topotaktischen Umwandlungen einer besonderen Form von Festen Lösungen und deren Untersuchung mittels Festkörper Kernspinresonanz (Solid State NMR) und Röntgen-Pulverdiffraktometrie. In Sodalithen {Na6[Al3Si3O12]2*(A,B)2} sind die Gast-spezies (A,B) bei denen es sich sowohl um Salze des Typs NaX als auch um Wasser oder basische Zentren handeln kann statistisch in den Aluminosilikat- Käfigen verteilt. Der nichtlineare Zusammenhang zwischen den Gastionen- Konzentrationen im Synthesegel und Sodalith wurde untersucht für die Systeme (NaX, NaY) mit X,Y = Cl-, Br-, I-, O2H3- und durch ein empirisches Modell beschrieben. Basische Zentren können topotaktisch durch Wasser ersetzt werden, welches den Sodalith bei 400°C verlässt. Durch Bedampfen des trockenen Sodaliths mit elementarem Natrium können (Na4)3+ Farb-Zentren (F-centers) erzeugt werden. Zusammenhänge zwischen NMR Parametern von 1H, 23Na, 27Al, 29Si, 35Cl, 81Br und 127I Kernen und ihrer lokalen Umgebung konnten aufgezeigt und zur Charakterisierung genutzt werden. Schließlich geben temperaturabhängige NMR Untersuchungen Aufschluss über die elektrostatischen und magnetischen Wechselwirkungen zwischen den paramagnetischen Elektronen der F-Zentren

NMR investigations on the lithiation and delithiation of nanosilicon-based anodes for Li-ion batteries

Lithiation and delithiation of nanosilicon anodes of 100-200 nm diameter have been probed by ex situ solid-state high-resolution 7Li nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM) methods. Samples were charged within pouch cells up to capacities of 1,500 mAh/g at 0.1 C, and subsequently discharged at the same rate. The NMR spectra reveal important quantitative information on the local lithium environments during the various stages of the charging/discharging process. The TEM experiments show that the electrochemical lithiation of nanosilicon particles results in core-shell materials, consisting of Li xSi shells surrounding a core of residual silicon. The NMR spectra yield approximate Li/Si ratios of the lithium silicides present in the shells, based on the distinct local environments of the various types of 7Li nuclei present. The combination of NMR with TEM gives important quantitative conclusions about the nature of the electrochemical lithiation process: Following the initial formation of the solid electrolyte interphase layer, which accounts for an irreversible capacity of 240 mAh/g, lithium silicide environments with intermediate Li concentrations (Li 12Si 7, Li 7Si 3, and Li 13Si 4) are formed at the 500 to 1,000 mAh/g range during the charging process. At a certain penetration depth, further lithiation does not progress any further toward the interior of the silicon particles but rather leads to the formation of increasing amounts of the lithium-richest silicide, Li 15Si 4-type environments. Delithiation does not result in the reappearance of the intermediate-stage phases but rather only changes the amount of Li 15Si 4 present, indicating no microscopic reversibility. Based on these results, a detailed quantitative model of nanophase composition versus penetration depth has been developed. The results indicate the power and potential of solid-state NMR spectroscopy for elucidating the charging/discharging mechanism of nano-Si anodes. © 2010 Springer-Verlag

The duration of sociosexual behaviors in male meadow voles Microtus pennsylvanicus varies before, during, and after copulation

The behaviors that surround copulation are characterized as sociosexual behaviors. These behaviors displayed by males that are directed at females may include allogrooming, wrestling, chasing, approach, and time spent together. The data supported the hypothesis that the duration of sociosexual behaviors differs during the pre-copulatory, peri-copulatory, and post-copulatory phases of the mating bout in meadow voles. Voles spent more time approaching conspecifics during the pre- and peri-copulatory phases than during the post-copulatory phase. Voles spent more time allogrooming, wrestling, and chasing during the pre-copulatory phase than during the peri- and post-copulatory phases. Voles spent similar amounts of time together during the pre-, peri-, and post-copulatory phases. The data suggest that sociosexual behaviors displayed by males may be involved in setting the pace and temporal components of the mating bout. During the pre-copulatory phase particular behaviors by male voles may attract females, during the peri-copulatory phase some of these behaviors may stimulate or motivate the female to mate, and during the post-copulatory phase certain behaviors may prepare the male to mate again [Current Zoology 57 (1): 43–49, 2011]