Formation Of Nanocrystalline Materials Research Articles

Oxidative Addition to SnII Guanidinate Complexes: Precursors to Tin(II) Chalcogenide Nanocrystals

SnS, SnSe and SnTe are potentially important semiconductor materials. Here, we describe the application of chalcogen containing SnIV guanidinate precursors for the production of tin(II) chalcogenide nanocrystals. Reaction of the stannylene(II) guanidinate complex [{Me2NC(NCy)2}2Sn] (1) with Ph2E2 (E = S, Se, Te), and CBr4 forms the SnIV complexes [{Me2NC(NCy)2}2Sn(Ch‐Ph)2] (2–4) and [{Me2NC(NCy)2}2SnBr2] (5), respectively. Complex 5 has been subsequently used for the synthesis of the corresponding SnIV mono chalcogenide complexes, [{Me2NC(NCy)2}2Sn = E] (6–8) by the reaction of 5 with Li2E systems. Isolated tin complexes have characterized by elemental analysis, NMR spectroscopy, and the molecular structures of complexes 2–5 determined by single‐crystal X‐ray diffraction. TG analysis showed that complexes 2–4 and 6–8 all have residual masses close to those expected for the formation of the corresponding “SnE” systems. Complexes 6–8 were assessed for their utility in the formation of nanocrystalline materials. The materials obtained were characterized by powder X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM) and energy dispersive X‐ray analysis (EDX). Analysis showed formation of SnSe and SnTe from complexes 7 and 8, respectively.

Microstructures and mechanical properties of nanocrystalline NiTi intermetallics formed by mechanosynthesis

The formulation of nanocrystalline NiTi shape memory alloys has potential effects in mechanical stimulation and medical implantology. The present work elucidates the effect of milling time on the product’s structural characteristics, chemical composition, and microhardness for NiTi synthesized by mechanical alloying for different milling durations. Increasing the milling duration led to the formation of a nanocrystalline NiTi intermetallic at a higher level. The formation of nanocrystalline materials was directed through cold fusion, fracturing, and the development of a steady state, which were influenced by the accumulation of strain energy. In the morphological study, uninterrupted cold diffusion and fracturing were visualized using transmission electron microscopy. Particle size analysis revealed that the mean particle size was reduced to ~93 μm after 20 h of milling. The mechanical strength was enhanced by the formation of a nanocrystalline intermetallic phase at longer milling time, which was confirmed by the results of Vickers hardness analyses.

Sol-Gel Synthesis and Characterization of Nanoparticles

The nanoparticles have been synthesized by sol-gel technique. X-ray diffraction, scanning electron microscopy, optical absorption spectroscopy, and electron paramagnetic resonance spectroscopy were used to characterize the sample. The X-ray diffraction results indicate the formation of nanocrystalline materials in tetragonal lattice with P42/nnm space group. The identical distribution of elements were confirmed by scanning electron microscopy with energy dispersive X-ray spectrometry and X-ray mapping. Electron paramagnetic resonance lineshapes of the samples are obtained at various (13 K, 77 K, and 300 K) temperatures. The isotropic lineshapes of the sample B1 are attributed to dipole-dipole interaction of Ti3+ ions. The incorporation of Al3+ ions into the sample B2–B5 the isotropic nature of the lineshapes are collapsed due to the distraction in crystal field. Optical absorption spectra results reveal the presence of Ag-TiO2 nanoparticles.

Nanocrystalline LiCo 1− xNi xO 2 (0≤ x≤0.3) for Li-ion batteries

Nanocrystalline LiCo 1− x Ni x O 2 (0≤ x≤0.3)—a promising cathode material for rechargeable lithium batteries has been successfully prepared by a novel soft chemical route. Both the formation of the metal–glycine complex and subsequent decomposition of the same at low temperatures under carefully controlled oxygen flow play a critical role in the formation of nanocrystalline material. The thermal history of the as-prepared gel is established by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm the formation of layered α-NaFeO 2 structure at temperature as low as 330 °C. The exothermic combustion reaction of the organic precursors, which generates high temperature, should be avoided as it results in the spontaneous growth of large crystals. High-resolution transmission electron microscopy (HRTEM) investigation reveals that the particle size of LiCo 0.7Ni 0.3O 2 heated at 400 °C is in the range of 10–15 nm. Substitution of nickel retards the crystal growth. Solid state 6Li-Magic Angle Spinning (MAS) NMR investigation reveals that the micro-structural short range ordering of nickel ions in LiCo 1− x Ni x O 2 (0≤ x≤0.3) is minimum at lower processing temperatures. 6Li-MAS NMR studies show that considerable amount of short range ordering of nickel ions is observed when the calcination temperature is raised beyond 800 °C indicating that the upper limit for processing temperature is around 750 °C. These materials were fabricated into thin electrodes using polyvinylidene fluoride (PVDF) as polymer binder and the electrochemical properties such as charge/discharge and impedance were evaluated. The electrodes cycled well with a coulombic efficiency of close to one.

Formation of Nanocrystalline Materials by Crystallization of Metallic Glasses

Formation of Nanocrystalline Materials by Crystallization of Metallic Glasses