Synthesis and characterization of a series of nickel(II) alkoxide precursors and their utility for Ni(0) nanoparticle production

A series of nickel(ii) aryloxide ([Ni(OAr)2(py)x]) precursors was synthesized from an amide-alcohol exchange using [Ni(NR2)2] in the presence of pyridine (py). The H-OAr selected were the mono- and di-ortho-substituted 2-alkyl phenols: alkyl = methyl (H-oMP), iso-propyl (H-oPP), tert-butyl (H-oBP) and 2,6-di-alkyl phenols (alkyl = di-iso-propyl (H-DIP), di-tert-butyl (H-DBP), di-phenyl (H-DPhP)). The crystalline products were solved as solvated monomers and structurally characterized as [Ni(OAr)2(py)x], where x = 4: OAr = oMP (1), oPP (2); x = 3: OAr = oBP (3), DIP (4); x = 2: OAr = DBP (5), DPhP (6). The excited states (singlet or triplet) and various geometries of 1-6 were identified by experimental UV-vis and verified by computational modeling. Magnetic susceptibility of the representative compound 4 was fit to a Curie Weiss model that yielded a magnetic moment of 4.38(3)μB consistent with a Ni2+ center. Compounds 1 and 6 were selected for decomposition studied under solution precipitation routes since they represent the two extremes of coordination. The particle size and crystalline structure were characterized using transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD). The materials isolated from 1 and 6 were found by TEM to form irregular shape nanomaterials (8-15 nm), which by PXRD were found to be Ni0 hcp (PDF: 01-089-7129) and fcc (PDF: 01-070-0989), respectively

Magnetic and electrical properties of flux grown single crystals of Ln 6M 4Al 43 (Ln=Gd, Yb; M=Cr, Mo, W)

Millimeter-sized single crystals of Ln 6M 4Al 43 (Ln=Gd, Yb; M=Cr, Mo, W) were successfully grown with a molten aluminum flux. Synthetic conditions and physical properties for single crystals of all six analogs are discussed. The compounds exhibit metallic resistivity with room temperature values between 0.1 and 0.6 mΩ-cm. The Yb analogs are Pauli paramagnets with the Yb ion adopting the nonmagnetic divalent configuration (Yb 2). Gd 6Cr 4Al 43, Gd 6Mo 4Al 43, and Gd 6W 4Al 43 appear to order antiferromagnetically at 19, 15, and 15 K, respectively. © 2012 Elsevier Inc. All rights reserved

Substitution studies of Mn and Fe in Ln6W4Al 43 (Ln=Gd, Yb) and the structure of Yb6Ti 4Al43

The synthesis and characterization of Mn- and Fe-substituted Ln 6W4Al43 (Ln=Gd, Yb) and Yb6Ti 4Al43 are reported. The compounds adopt the Ho 6Mo4Al43 structure type with lattice parameters of a~11 Å and c~17.8 Å with structural site preferences for Mn and Fe. The magnetization of Yb6W4Al43 is sensitive to Mn and Fe doping, which is evident by an increase in the field dependent magnetization. Gd6W4Al43, Gd6W 4Al42.31(11)Mn0.69(11), and Gd 6W4Al41.69(12)Fe1.30(12) order antiferromagnetically in the ab- and c-directions at 15, 14, and 13 K, respectively, with positive Weiss constants, suggesting the presence of ferromagnetic exchange interactions. Anisotropic magnetization data of Gd 6W4Al43-yTy (T=Mn, Fe) analogs are discussed. © 2013 Published by Elsevier Inc

Serendipitous growth of single crystals with silicon incorporation

The self-flux method for crystal growth is a highly versatile technique which can be used to grow single crystals of congruently melting, incongruently melting, and even metastable phases. However, the growth of a single phase using the self-flux technique can be challenging yet rewarding, especially when one compound in a phase space is considerably more stable than the others. Herein, the synthesis, structure and properties of two competing metal silicide phases, Ru 23(Al,Si) 97 and CeRu 4(Al,Si) 15.58, and two competing polymorphs of CeAg ySi xGa 2-x-y, are discussed to provide an insight into the methods which can be used to target a single phase using the selfflux technique. © 2012 Taylor & Francis

Fabrication of Tantalum and Hafnium Carbide Fibers via ForcespinningTM for Ultrahigh-Temperature Applications

In this work, a novel method for producing ultrafine tantalum and hafnium carbide fibers using the ForcespinningTM technique via a nonhalide-based sol-gel process was investigated. An optimal solution viscosity range was systematically determined via rheological studies of neat PAN/DMF as a function of fiber formation. Subsequently, ForcespinningTM parameters were also systemically studied to determine the optimal rotational velocity and spinneret-to-collecting rod distance required for ideal fiber formation. TaC and HfC fibers were synthesized via ForcespinningTM utilizing a mixture of PAN and refractory transition metal alkoxides (i.e., tantalum (V) ethoxide and hafnium (IV) tert-butoxide) in DMF solution based on optimal conditions determined from the neat PAN/DMF. In all instances after calcination, powder X-ray diffraction (PXRD) and energy dispersive spectroscopy (EDS) indicated that TaC and HfC fibers were produced. TGA/DSC confirmed the chemical stability of the resulting fibers

Investigation of Fe incorporation in LnCr2Al20 (Ln = La, Gd, Yb) with 57Fe Mössbauer and Single Crystal X-ray Diffraction

International audienc

Investigation of Mn, Fe, and Ni Incorporation in CeCo₂Al₈

Single crystals of CeCo_2–<i>x</i>M_<i>x</i>Al₈ (M = Mn, Fe, Ni; 0 ≤ <i>x</i> < 1) were grown and characterized by X-ray diffraction and magnetic susceptibility. The unit cell volumes of Mn-doped compounds increase and those of Ni-doped compounds decrease with increasing dopant concentration. All samples display a magnetic ordering near 6 K with magnetic moments of the analogues ranging from 2.61 to 2.81 μ_B/mol Ce and slightly higher than Ce³⁺ only magnetic moment. The unit cell volumes of Fe-doped compounds also increase with increasing Fe concentration. However, the cell volume of CeCo_2–<i>x</i>Fe_<i>x</i>Al₈ decreases for <i>x</i> = 1.00 and is not Curie–Weiss possibly because of valence fluctuation

Investigation of Fe incorporation in LnCr₂Al₂₀ (Ln = La, Gd, Yb) with ⁵⁷Fe Mössbauer and Single Crystal X‑ray Diffraction

Crystal growth, structure determination, and magnetic properties of LnCr₂Al_{20‑<i>x</i>}Fe_<i>x</i> (Ln = La, Gd, Yb) adopting the CeCr₂Al₂₀ structure type with space group <i>Fd</i>3̅<i>m</i>, <i>a</i> ∼ 14.5 Å, are reported. Single crystal X-ray diffraction and Mössbauer spectroscopy are employed to fully characterize the crystal structure of LnCr₂Al_{20‑<i>x</i>}Fe_<i>x</i> (Ln = La, Gd, Yb). LnCr₂Al_{20‑<i>x</i>}Fe_<i>x</i> (Ln = La, Gd, Yb) are the first pseudoternaries adopting the CeCr₂Al₂₀ structure type with a transition metal occupying the main group site. The Yb analogues are Pauli paramagnets with the Yb ion adopting an electronic configuration close to Yb²⁺, while the Gd analogues show paramagnetic behavior with no magnetic order down to 3 K