Publications

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An evaluation of calcium tungsten oxide (CaWO4) nanoparticles' properties was conducted using the powders generated from an all-alkoxide solvothermal (SOLVO) route. The reaction involved a toluene/pyridine mixture of tungsten(V) ethoxide ([W(OEt)5]) with calcium bis(trimethyl silyl) amide ([Ca(N(Si(CH3)3)2]) modified in situ by a series of alcohols (H-OR) including neo-pentanol (H-OCH2C(CH 3)3 or H-ONep) or sterically varied aryl alcohols (H-OC6H3R2-2,6 where R = CH3 (H-DMP), CH(CH3)2 (H-DIP), C(CH3)3 (DBP))]. Attempts to identify the intermediates generated from this series of reactions led to the crystallographic identification of [(OEt) 4W(μ-OEt)2Ca(DBP)2] (1). Each different SOLVO generated "initial" powder was found by transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) to be nanomaterials roughly assigned as the scheelite phase (PDF 00-041-1431); however, these initial powders displayed no luminescent behavior as determined by photoluminescence (PL) measurements. Thermal processing of these powders at 450, 650, and 750 C yielded progressively larger and more crystalline scheelite nanoparticles. Both PL and cathodoluminescent (CL) emission (422-425 and 429 nm, respectively) were observed for the nanomaterials processed at 750 C. Ion beam induced luminescence (IBIL, 478 nm) appeared to be in agreement with these PL and CL measurements. Further processing of the materials at 1000 C, led to a coalescence of the particles and significant improvement in the observed PL (445 nm) and CL measurements; however, the IBIL spectrum of this material was significantly altered upon exposure. These data suggest that the smaller nanoparticles were more stable to radiation effects possibly due to the lack of energy deposits based on the short track length; whereas the larger particles appear to suffer from radiation induced structural defects. © 2013 American Chemical Society.

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The first step in an attempt to isolate Sco from a Wo crucible was explored by soaking the samples in a series of organic (HOAc) and inorganic (HCl, H2SO4, H3PO4, HNO3) acids. All samples, except the HOAc, yielded a powder. The weight loss suggests that HNO3 is the most efficient solvent; however, the powders were tentatively identified by PXRD and found to contain both W and Sc by-products. The higher weight loss may also indicate dissolution of the Wo crucible, which was further evidenced upon visual inspection of the crucible. The H3PO4 acid soak yielded the cleanest removal of Sc from the crucible. More work to understand the separation of the Sco from the Wo crucible is necessary but the acid routes appear to hold promise under not as of yet established criteria.

Lithium iron double aryloxides ([Li2Fe(OAr)4]) were synthesized, characterized, and investigated for use as precursors to LiFeO 2 nanomaterials. From the reaction of iron mesityl, two equivalents of lithium bis(trimethylsilyl) amide, and a series of monosubstituted [HOC 6H4(R)-2 where R = CH3 (oMP), CH(CH 3)2 (oPP), C(CH3)3 (oBP)] or disubstituted [HOC6H3(R)2-2,6 where R = CH 3 (DMP), CH(CH3)2 (DIP), C(CH3) 3 (DBP), C6H5 (DPhP)] aryl alcohols (H-OAr) in tetrahydrofuran (THF) or pyridine (py) were isolated. The mixed-cation Li-Fe precursors that were successfully isolated from this reaction were crystallographically identified as the double aryloxides [Fe((μ-OAr) 2Li(solv)2)2] (OAr = oPP: solv = THF (1), py (2); DMP/THF (3)) and the unusual salt [Li(THF)4][Fe(DBP) 3] (4). For the other OAr/solvent systems investigated, previously published Li or Fe alkoxide compounds or oils were isolated. Compounds 1-4 were further characterized using a variety of analytical methods but the paramagnetic nature of the Fe prevented NMR analyses. The mixed-cation precursors were used for production of nanomaterials following a solvothermal route using dioxane (in place of THF) or pyridine as the solvent. The final materials generated were characterized as the substituted lithium iron oxide structure (LiFeO 2; PDF 01-073-6306). Attempts to cycle the Li in these materials failed to demonstrate appreciable mobile capacity at reasonable potentials; however, a capacity of 87 mAh/g that quickly faded during cycling was observed at very low potentials (start: ∼0.6 V; end: 0.5 V versus Li). © 2013 Elsevier Ltd. All rights reserved.

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