Spectral-optical-electrical-thermal properties of deposited thin films of nano-sized calcium(II)-8-hydroxy-5,7-dinitroquinolate complex

Spectral–optical–electrical–thermal properties of deposited thin films of nano-sized calcium(II)-8-hydroxy-5,7-dinitroquinolate complex, Ca[((NO₂)₂-8HQ)₂], were explored, studied and evaluated in this work. Thin films of Ca[((NO₂)₂-8HQ)₂] were assembled by using a direct, simple and efficient layer-by-layer (LBL) chemical deposition technique. The optical properties of thin films were investigated by using spectrophotometric measurements of transmittance and reflectance at normal incidence in the wavelength range 200–2500 nm. The refractive index, n, and the absorption index, k, of Ca[((NO₂)₂-8HQ)₂] films were determined from the measured transmittance and reflectance. The real and imaginary dielectric constants were also determined. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region reveals a direct allowed transition with band gaps of 1.1 eV and 2.4 eV for the optical and transport energy gaps, respectively. The current–voltage characteristics of Ca[((NO₂)₂-8HQ)₂] showed a trap-charge limited conduction in determining the current at the intermediate and high bias regimes. Graphical representation of the current–voltage characteristics yields three distinct linear parts indicating the existence of three conduction mechanisms. Structural characterization and identification were confirmed by using Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy (SEM) was also used to image the surface morphology of the deposited nano-sized metal complex and such study revealed a high homogeneity in surface spherical particle distribution with average particles size in the range 20–40 nm. Thermal gravimetric analysis (TGA) was also studied for [(NO₂)₂-8HQ] and Ca[((NO₂)₂-8HQ)₂] to evaluate and confirm the thermal stability characteristics incorporated into the synthesized nano-sized Ca[((NO₂)₂-8HQ)₂] complex.     

Mechanosynthesis of spinel ferrite nanoparticles followed by Mössbauer spectroscopy

The single-step synthesis of nanosized MgFe₂O₄ and NiFe₂O₄ via mechanochemical processing of binary oxide precursors is followed by ⁵⁷Fe Mössbauer spectroscopy. Quantitative information is provided on both ionic and spin configurations in mechanosynthesized spinels. The response of the mechanosynthesized ferrite nanoparticles to changes in temperature is also studied.     

Fe valence state at the surface of the Fe0.5Cu0.5Cr2S4 spinel

Here we present X‐ray absorption measurements of a vacuum cleaved Fe_0.5Cu_0.5Cr₂S₄ single crystal. Measurements at different positions on the cleaved sample surface clearly reveal a difference between the valence state of the Fe ions in the sur‐ face layers and the valency of the Fe ions present in the bulk. These results confirm the findings of recent measurements outlined previously. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Adsorption of Nin (n=1 -4) clusters on perfect and O-defective CuAl2O4 surfaces: A DFT study

The adsorption energies for single Ni atom on CuAl₂O₄(100) and (110) surfaces are 5.30 and 4.08 eV, respectively. The growth and aggregation of Ni can be effectively inhibited on the perfect CuAl₂O₄(100) surface. The adsorption of Ni on the spinel surface is accompanied by charge transfer. The interaction of Ni with CuAl₂O₄ surface is stronger than with the γ-Al₂O₃(110) surface.     

Location of the Spinel Vacancies in γ‐Al2O3

A non‐spinel model for the structure of γ‐Al₂O₃, with 25 % of the Al³⁺ cations at tetrahedral positions, has been the subject of wide interest. However, ¹⁷O NMR measurements and, more recently, ²⁷Al NMR measurements have shown that there are considerably more Al³⁺ cations at tetrahedral positions. This means that the Al³⁺ vacancies in γ‐Al₂O₃ are not at tetrahedral but at octahedral positions, as in isostructural γ‐Fe₂O₃ and in accordance with density functional theory predictions. This has consequences with regard to the surface structure of γ‐Al₂O₃, and thus, for catalysis.     

Micro‐Raman investigation of nanosized zinc ferrite: effect of crystallite size and fluence of irradiation

Zinc ferrite nanoparticles of different sizes ranging from 12 to 62 nm were synthesized by using the nitrate route. These nanoparticles were irradiated by a 100 MeV oxygen beam at two fluences: 1 × 10¹³ and 5 × 10¹³ ions/cm². It was observed that modes corresponding to cubic spinel phase were retained after the irradiation in all the systems. The variation in the parameters of various modes follows phonon confinement, while this effect seems to violate in irradiated specimen. It was found that the irradiation‐induced changes in the modes F_2g(2) and F_2g(3) depend on whether the crystallite size of the pristine sample is less than, equal to or greater than the phonon confinement length, while this length is not dominant for the irradiation‐induced changes in the mode A_1g. The changes in various parameters of the modes are attributed to the combined effect of the restructuring of the chemical species and ion‐induced defects. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantum mechanical modeling of Zn-based spinel oxides: Assessing the structural,vibrational, and electronic properties

The structural, electronic, and vibrational properties of two leading representatives of the Zn-based spinel oxides class, normal ZnX₂O₄ (X = Al, Ga, In) and inverse Zn₂MO₄ (M = Si, Ge, Sn) crystals, were investigated. In particular, density functional theory (DFT) was combined with different exchange-correlation functionals: B3LYP, HSE06, PBE0, and PBESol. Our calculations showed good agreement with the available experimental data, showing a mean percentage error close to 3% for structural parameters. For the electronic structure, the obtained HSE06 band-gap values overcome previous theoretical results, exhibiting a mean percentage error smaller than 10.0%. In particular, the vibrational properties identify the significant differences between normal and inverse spinel configurations, offering compelling evidence of a structure-property relationship for the investigated materials. Therefore, the combined results confirm that the range-separated HSE06 hybrid functional performs the best in spinel oxides. Despite some points that cannot be directly compared to experimental results, we expect that future experimental work can confirm our predictions, thus opening a new avenue for understanding the structural, electronic, and vibrational properties in spinel oxides.     

纳米尺度NiLa2O4尖晶石催化NaBH4还原亚胺制仲胺

由溶胶-凝胶法制得的Ni-La化合物经热分解制备了纳米尺度NiLa2O4尖晶石，在750 oC焙烧后形成了结晶良好的尖晶石结构.采用差热分析、X射线衍射、透射电镜、扫描电镜和粒度分布分析等手段表征了该尖晶石的物理化学性质.结果表明，该纳米颗粒有规则的外形和确定的晶面，由平均粒径为40 nm的规整半球晶粒组成.精修的晶胞参数a=3.861205?和c=12.6793?.在NaBH4选择还原亚胺制相应仲胺的反应中，该新型纳米NiLa2O4尖晶石可用作高效多相催化剂，得到了较高的产物产率.所有反应可在室温和相对较短的时间内完成.在优化的反应条件下，均可得到带有不同芳基的，包括带有吸电子和供电子基团的仲胺.该催化剂回收简便，重复使用4次，其催化活性未见明显下降.     

Preparation and performance of (Co,Mn)3O4 spinel coating on Crofer alloy by composite electrodeposition and step-heating thermal conversion

The preparation and performance improvement of the spinel coating on the surface of ferritic alloy is of wide interest for its application in the metallic interconnects of the solid oxide fuel cells (SOFCs). The Co Mn₂O₃ composite coating is prepared on the surface of the Crofer alloy by the composite electrodeposition method. A step-heating thermal conversion process is subsequently used to convert the composite coating into a spinel coating, while a direct-heating process is implemented as the control experiment. Isothermal oxidation tests are then carried out for the prepared samples in order to present the high temperature performance. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and area-specific resistance (ASR) are used to analyze the properties of the matrix and coatings. The experimental results reveal that the coatings by step-heating thermal conversion exhibit better performance of electrical conductivity and oxidation resistance than the coatings by direct-heating process. Furthermore, with the increase of oxidation time, the atomic proportion of Cr element diffusing to the surface of the matrix is maintained at about 3%–4% for the samples with spinel coatings by step heating, which effectively prevent the Cr volatilization in the matrix. The preparation of spinel coatings on the ferritic alloy by composite electrodeposition and step-heating thermal conversion is helpful to stimulate new ideas for the development of reliable and cost-effective metallic interconnect.