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ABSTRACT: The sintering temperature of the LiAlSiO4(LAS) ceramics, which exhibited the microwave dielectric properties of εr = 4.8, Q × f = 36 000GHz, and τf=8.0 ppm/°C, decreased below 960°C when B2O3 was added. The B2O3-related liquid phase was formed and assisted the densification of the LAS ceramics at low temperatures. The average grain size of the specimen sintered at 950°C increased with the addition of B2O3 but decreased when B2O3 exceeded 12.0 mol%, probably due to the presence of a large amount of liquid phase. The LAS ceramics containing 12.0 mol% of B2O3 sintered at 950°C exhibited the excellent microwave dielectric properties of εr = 5.3, Q×f = 212 000GHz and τf =-7.7 ppm/°C.
Journal of the American Ceramic Society 05/2011; 94(7):1995 - 1998. · 2.27 Impact Factor
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ABSTRACT: The preparation of gold nanoparticle (AuNP) assemblies was conducted by the synthesis and dipolar assembly of ferromagnetic core-shell nanoparticles composed of AuNP cores and cobalt NP shells. Dissolution of metallic Co phases with mineral acids afforded self-assembled AuNP chains and bracelets.
Chemical Communications 11/2010; 47(3):890-2. · 6.17 Impact Factor
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ABSTRACT: The preparation of cobalt oxide nanowires with gold nanoparticle (AuNP) inclusions (Au−Co3O4 nanowires) via colloidal polymerization of dipolar core−shell NPs is reported. Polystyrene-coated ferromagnetic NPs composed of a dipolar metallic cobalt shell and a gold NP core (PS−AuCoNPs) were synthesized by thermolysis of octacarbonyldicobalt [Co2(CO)8] in the presence of AuNP seeds and polymeric ligands. The colloidal polymerization process of these dipolar PS−AuCoNPs comprises dipolar nanoparticle assembly and solution oxidation of preorganized NPs to form interconnected cobalt oxide nanowires via the nanoscale Kirkendall effect, with AuNP inclusions in every repeating unit of the one-dimensional mesostructure. Calcination of the polymer-coated nanowires afforded polycrystalline Au−Co3O4 nanowires that were determined to be electroactive. Nanocomposite materials were characterized by transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, and cyclic voltammetry. We demonstrate that the optical and electrochemical properties of Au−Co3O4 nanowires are significantly enhanced in comparison with hollow Co3O4 nanowires prepared via colloidal polymerization.
02/2010;
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ABSTRACT: The preparation of cobalt oxide nanowires with gold nanoparticle (AuNP) inclusions (Au-Co(3)O(4) nanowires) via colloidal polymerization of dipolar core-shell NPs is reported. Polystyrene-coated ferromagnetic NPs composed of a dipolar metallic cobalt shell and a gold NP core (PS-AuCoNPs) were synthesized by thermolysis of octacarbonyldicobalt [Co(2)(CO)(8)] in the presence of AuNP seeds and polymeric ligands. The colloidal polymerization process of these dipolar PS-AuCoNPs comprises dipolar nanoparticle assembly and solution oxidation of preorganized NPs to form interconnected cobalt oxide nanowires via the nanoscale Kirkendall effect, with AuNP inclusions in every repeating unit of the one-dimensional mesostructure. Calcination of the polymer-coated nanowires afforded polycrystalline Au-Co(3)O(4) nanowires that were determined to be electroactive. Nanocomposite materials were characterized by transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, and cyclic voltammetry. We demonstrate that the optical and electrochemical properties of Au-Co(3)O(4) nanowires are significantly enhanced in comparison with hollow Co(3)O(4) nanowires prepared via colloidal polymerization.
Journal of the American Chemical Society 02/2010; 132(10):3234-5. · 9.91 Impact Factor
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ABSTRACT: The synthesis and electrochemical characterization of ferrocene functional polymethacrylate brushes on indium tin oxide (ITO) electrodes using surface-initiated atom transfer radical polymerization (SI-ATRP) is reported. SI-ATRP of ferrocene-containing methacrylate (FcMA) monomers from a phosphonic acid initiator-modified ITO substrate yielded well-defined homo- and block (co)polymer brushes of varying molar mass (4,000 to 37,000 g/mol). Correlation of both electrochemical properties and brush thicknesses confirmed controlled SI-ATRP from modified ITO surfaces. The preparation of block copolymer brushes with varying sequences of FcMA segments was conducted to interrogate the effects of spacing from the ITO electrode surface on the electrochemical properties of a tethered electroactive film.
Langmuir 12/2009; 26(3):2083-92. · 4.19 Impact Factor
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Pei Yuin Keng, Bo Yun Kim,
In-Bo Shim,
Rabindra Sahoo,
Peter E Veneman,
Neal R Armstrong,
Heemin Yoo,
Jeanne E Pemberton,
Mathew M Bull,
Jared J Griebel,
Erin L Ratcliff,
Kenneth G Nebesny,
Jeffrey Pyun
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ABSTRACT: The preparation of polystyrene-coated cobalt oxide nanowires is reported via the colloidal polymerization of polymer-coated ferromagnetic cobalt nanoparticles (PS-CoNPs). Using a combination of dipolar nanoparticle assembly and a solution oxidation of preorganized metallic colloids, interconnected nanoparticles of cobalt oxide spanning micrometers in length were prepared. The colloidal polymerization of PS-CoNPs into cobalt oxide (CoO and Co(3)O(4)) nanowires was achieved by bubbling O(2) into PS-CoNP dispersions in 1,2-dichlorobenzene at 175 degrees C. Calcination of thin films of PS-coated cobalt oxide nanowires afforded Co(3)O(4) metal oxide materials. Transmission electron microscopy (TEM) revealed the formation of interconnected nanoparticles of cobalt oxide with hollow inclusions, arising from a combination of dipolar assembly of PS-CoNPs and the nanoscale Kirkendall effect in the oxidation reaction. Using a wide range of spectroscopic and electrochemical characterization techniques, we demonstrate that cobalt oxide nanowires prepared via this novel methodology were electroactive with potential applications as nanostructured electrodes for energy storage.
ACS Nano 10/2009; 3(10):3143-57. · 10.77 Impact Factor
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ABSTRACT: Novel complexes 1 and 2 based on N-heterocyclic carbenes, which are analogous to Ru(bpy)(3)(2+) and Ru(terpy)(2)(2+), respectively, were synthesized. The complex, which is analogous to Ru(terpy)(2)(2+), exhibited promising photoluminescence properties with a long lifetime of 820 ns in acetonitrile and 3100 ns in water at room temperature, respectively. In addition, ab initio calculations were carried out.
Inorganic Chemistry 12/2004; 43(22):6896-8. · 4.60 Impact Factor
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ABSTRACT: A novel coordination polymer containing Co(NCS)2 and a rigid ligand, 2,5-bis(4-pyridylethynyl)-thiophene showing unusual flexibility was synthesized.
Chemical Communications 11/2003; · 6.17 Impact Factor
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ABSTRACT: Chiral ferrocenyl imidazolium salts were obtained from optically pure ferrocenyl alcohols or acetates by substitution with retention of configurations. Their rhodium and iridium complexes were synthesized and applied to asymmetric hydrogenations. The benzimidazolylidene−iridium complex showed up to 52.6% ee in the transfer hydrogenation of 4‘-methylacetophenone.
10/2003;
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ABSTRACT: Three cylindrical nanotubular supramolecular structures (S1, S2, and S3) were synthesized by self-assembly of Co(NCS)2 with 1,3-diimidazolyl benzene (L1), 1,2-diimidazolyl benzene (L2), or 2,6-diimidazolyl pyridine (L3), respectively. They all showed similar top views. Columnar packing or assembly of helices was used to explain the construction of tubular materials with bent ligands. The supramolecular material, S1, derived from L1 was a tubular structure based on columnar packing, and others formed from L2 or L3 were similar structures based on the assembly of helices and were a rare example of Meso-helical architectures. These three tubular materials showed interesting 3-D-packing features because of various π−π interactions between 2-D supramolecules. The free heteroatom, nitrogen, in L3 plays an important role in determining the supramolecular structures. The structures show very high thermal stability up to 291 °C for Co(NCS)2(L1)2, 300 °C for Co(NCS)2(L2)2, and 256 °C for Co(NCS)2(L3)2, respectively. Crystal data for the three structures: Co(NCS)2(L1)2, monoclinic, C2/m, a = 7.403(1) Å, b = 17.561(1) Å, c = 10.275(1) Å, β = 107.201(4)°, V = 1276.0(2) Å3, Z = 4; Co(NCS)2(L2)2, orthorhombic, Cmca, a = 7.868(1) Å, b = 18.614(1) Å, c = 7.794(1) A, V = 2592.2(4) Å3, Z = 8; Co(NCS)2(L3)2, monoclinic, P21/n, a = 11.1230(1) Å, b = 9.2170(1) Å, c = 12.8680(1) Å, β = 95.967(2)°, V = 1312.1(2) Å3, Z = 4.
05/2003;
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ABSTRACT: Chiral imidazolium salts bearing sulfide and phosphine have been synthesized from chiral ferrocenylamine, and their rhodium and iridium complexes have been characterized by an X-ray diffraction study.
01/2003;
