Spin-glass-like behavior of uncompensated surface spins in NiO nanoparticulated powder

Nickel oxide nonoparticles successfully synthesized by a polymer percursor method are studied in this work. The analysis of X-ray powder diffraction data provides a mean crystallite size of 22 +/- 2 nm which is in a good agreement with the mean size estimated from transmission electron microscopy images. Whereas the magnetization (M) vs. magnetic field (H) curve obtained at 5 K is consistent with a ferromagnetic component which coexists with an antiferromagnetic component, the presence of two peaks in the zero-field-cooled trace suggests the occurrence of two blocking process. The broad maximum at high temperature was associated with the thermal relaxation of uncompensated spins at the particle core and the low temperature peak was assigned to the freeze of surface spins clusters. Static and dynamic magnetic results suggest that the correlations of surface spins clusters show a spin-glass-like below T-g = 7.3 +/- 0.1 K with critical exponents zv = 9.7 +/- 0.5 and beta = 0.7 +/- 0.1, which are consistent with typical reported for spin-glass systems. (C) 2012 Elsevier B.V. All rights reserved.

X-ray absorption spectroscopy study on La0.6Sr0.4CoO3 and La0.6Sr0.4Co1¡yFeyO3 nanotubes and nanorods for IT-SOFC cathodes.

In the last years, extensive research has been devoted to develop novel materials and structures with high electrochemical performance for intermediate-temperatures solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of La0:6Sr0:4CoO3 (LSCO) and La0:6Sr0:4Co1¡yFeyO3 (LSCFO) nanostructured cathodes, finding that they exhibit excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples were calcined at 1000oC in order to produce materials with the desired perovskite-type crystal structure. In this work, we analyze the oxidation states of Co and Fe and the local atomic order of LSCO and LSCFO nanotubes and nanowires for various compositions. For this pur- pose we performed XANES and EXAFS studies on both Co and Fe K edges. These measurements were carried out at the D08B-XAFS2 beamline of the Brazilian Synchrotron Light Laboratory (LNLS). XANES spectroscopy showed that Co and Fe only change slightly their oxidation state upon Fe addition. Surprisingly, XANES results indicated that the content of oxygen vacancies is low, even though it is well-known that these materials are mixed ionic-electronic conductors. EXAFS results were consistent with those expected according to the rhombohedral crystal structure determined in previous X-ray powder dffraction investigations. [1] M.G. Bellino et al, J. Am. Chem. Soc. 129 (2007) 3066 [2] J.G. Sacanell et al., J. Power Sources 195 (2010) 1786

Chiral Templating Activity of Tris(bipyridine)ruthenium(II) Cation in the Design of Three-Dimensional (3D) Optically Active Oxalate-Bridged {[Ru(bpy) 3 ][Cu 2 x Ni 2(1 - x ) (C 2 O 4 ) 3 ]} n (0 ≤ x ≤ 1; bpy = 2,2‘-bipyridine): Structural, Optical, and Magnetic Studies

Three-dimensional oxalate-based {[Ru(bpy)3][Cu2xNi2(1-x)(ox)3]}n (0≤ x ≤ 1, ox = C2O42-, bpy = 2,2‘bipyridine) were synthesized. The structure was determined for x = 1 by X-ray diffraction on single crystal. The compound crystallizes in the cubic space group P4132. It shows a three-dimensional 10-gon 3-connected (10,3) anionic network where copper(II) has an unusual tris(bischelated) environment. X-ray powder diffraction patterns and their Rietveld refinement show that all the compounds along the series are isostructural and single-phased. According to X-ray absorption spectroscopy, copper(II) and nickel(II) have an octahedral environment, respectively elongated and trigonally distorted. As shown by natural circular dichroism, the optically active forms of {[Ru(bpy)3][CuxNi2(1-x)(ox)3]}n are obtained starting from resolved Δ- or Λ-[Ru(bpy)3]2+. The Curie−Weiss temperatures range between −55 (x = 1) and −150 K (x = 0). The antiferromagnetic exchange interaction thus decreases when the copper contents increases in agreement with the crystallographic structure of the compounds and the electronic structure of the metal ions. At low temperature, the compounds exhibit complex long-range ordered magnetic behavior.

Bioactive glass sol-gel foam scaffolds:evolution of nanoporosity during processing and in situ monitoring of apatite layer formation using small- and wide-angle X-ray scattering

Recent work has highlighted the potential of sol-gel-derived calcium silicate glasses for the regeneration or replacement of damaged bone tissue. The work presented herein provides new insight into the processing of bioactive calcia-silica sol-gel foams, and the reaction mechanisms associated with them when immersed in vitro in a simulated body fluid (SBF). Small-angle X-ray scattering and wide-angle X-ray scattering (diffraction) have been used to study the stabilization of these foams via heat treatment, with analogous in situ time-resolved data being gathered for a foam immersed in SBF. During thermal processing, pore sizes have been identified in the range of 16.5-62.0 nm and are only present once foams have been heated to 400 degrees C and above. Calcium nitrate crystallites were present until foams were heated to 600 degrees C; the crystallite size varied from 75 to 145 nm and increased in size with heat treatment up to 300 degrees C, then decreased in size down to 95 rim at 400 degrees C. The in situ time-resolved data show that the average pore diameter decreases as a function of immersion time in SBF, as calcium phosphates grow on the glass surfaces. Over the same time, Bragg peaks indicative of tricalcium phosphate were evident after only 1-h immersion time, and later, hydroxycarbonate apatite was also seen. The hydroxycarbonate apatite appears to have preferred orientation in the (h,k,0) direction.

Deformation microstructure under nanoindentations in Cu using 3D x-ray structural microscopy

We have used a recently developed x-ray structural microscopy technique to make nondestructive, submicron-resolution measurements of the deformation microstructure below a 100mN maximum load Berkovich nanoindent in single crystal Cu. Direct observations of plastic deformation under the indent were obtained using a ~0.5 µm polychromatic microbeam and diffracted beam depth profiling to make micron-resolution spatially-resolved x-ray Laue diffraction measurements. The local lattice rotations underneath the nanoindent were found to be heterogeneous in nature as revealed by geometrically necessary dislocation (GND) densities determined for positions along lines beneath a flat indent face and under the sharp Berkovich indent blade edges. Measurements of the local rotation-axes and misorientation-angles along these lines are discussed in terms of crystallographic slip systems.

Vibrational spectroscopy of intercalated kaolinites. Part I

The industrial application of kaolinite is closely related to its reactivity and surface properties. The reactivity of kaolinite can be tested by intercalation, i.e. via the insertion of low molecular weight organic compounds between the kaolinite layers resulting in the formation of a nano-layered organo-complex. Although intercalation of kaolinite is an old and ongoing research topic, there is a limited knowledge available on the reactivity of different kaolinites, the mechanism of complex formation as well as on the structure of the complexes formed. Grafting and incorporation of exfoliated kaolinite in polymer matrices and other potential applications can open new horizons in the study of kaolinite intercalation. This paper attempts to summarize (without completion) the most recent achievements in the study of kaolinite organo-complexes obtained with the most common intercalating compounds like urea, potassium acetate, dimethyl sulphoxide, formamide and hydrazine using vibrational spectroscopy combined with X-ray powder diffraction and thermal analysis.

Development of descriptor tools for the characterization of Australian sugar mill evaporator scale

Cleaning of sugar mill evaporators is an expensive exercise. Identifying the scale components assists in determining which chemical cleaning agents would result in effective evaporator cleaning. The current methods (based on x-ray diffraction techniques, ion exchange/high performance liquid chromatography and thermogravimetry/differential thermal analysis) used for scale characterisation are difficult, time consuming and expensive, and cannot be performed in a conventional analytical laboratory or by mill staff. The present study has examined the use of simple descriptor tests for the characterisation of Australian sugar mill evaporator scales. Scale samples were obtained from seven Australian sugar mill evaporators by mechanical means. The appearance, texture and colour of the scale were noted before the samples were characterised using x-ray fluorescence and x-ray powder diffraction to determine the compounds present. A number of commercial analytical test kits were used to determine the phosphate and calcium contents of scale samples. Dissolution experiments were carried out on the scale samples with selected cleaning agents to provide relevant information about the effect the cleaning agents have on different evaporator scales. Results have shown that by simply identifying the colour and the appearance of the scale, the elemental composition and knowing from which effect the scale originates, a prediction of the scale composition can be made. These descriptors and dissolution experiments on scale samples can be used to provide factory staff with an on-site rapid process to predict the most effective chemicals for chemical cleaning of the evaporators.

Formation of thermodynamically unstable calcium oxalate dihydrate in sugar mill evaporators

Calcium oxalate (CaOX) is the most intractable scale component to remove in sugar mill evaporators by either mechanical or chemical means. The operating conditions of sugar mill evaporators should preferentially favour the formation of the thermodynamically stable calcium oxalate monohydrate (COM), yet analysis of scale deposit from different sugar factories have shown that calcium oxalate dihydrate (COD) is usually the predominant phase, and in some cases is the only hydrate formed. The effects of trans-aconitic, succinic and acetic acids, all of which are present in sugarcane juice, and ethylenediamine tetraacetic acid disodium salt (EDTA) on the growth of CaOX crystals have been examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and thermogravimetric analysis (TGA). trans-Aconitic acid, which constitutes two-thirds of the organic acid component in sugarcane juice, in the presence of sugar resulted in the formation of COD and COM in a 3:1 ratio. EDTA was the most effective acid to promote the formation of COD followed by trans-aconitic acid, then acetic acid and lastly succinic acid.

High-pressure Raman spectroscopic and other structural studies of hydrotalcites containing intercalated dicarboxylic acid anions

The results of pressure-tuning Raman spectroscopic, X-ray powder diffraction and solid-state 13C-NMR studies of selected dicarboxylate anions intercalated in a Mg-Al layered double hydroxide (talcite) lattice are reported. The pressure dependences of the vibrational modes are linear for pressures up to 4.6 GPa indicating that no phase transitions occur. The interlayer spacings show that the oxalate, malonate and succinate dianions are oriented perpendicular to the layers, but the glutarate and adipate are tilted. The solid-state 13C-NMR spectra of these materials show full chemical shift anisotropy and, therefore, the anions are not mobile at room temperature.

Hydrothermal synthesis of single crystallin strontium titanate nanocubes

Strontium titanate nanocubes with an average edge length of 150mm have been successfully synthesized from a simple hydrothermal system. Characterization techniques such as X-ray powder diffraction analysis, scanning electron microscopy and energy-dispersive analysis of X-rays were used to investigate the products. The results showed that as-prepared powders are pure SrTiO3 with cubic shape, which consists with the growth habit of its intrinsic crystal structure. These uniform nanocubes with high crystallinity will exhibit superior physical properties in the practical applications. Furthermore, during the experimental process, it has been found that the dilute acid washing process is very important to obtain high pure SrTiO3.

Moisture uptake and tensile properties of starch-sugar cane fibre films

THERE is an increasing need for biodegradable plastics because they are environmentally friendly and can replace petroleum-based non-degradable plastics which pollute the environment. Starch-derived films reinforced with sugar cane bagasse fibre, which are biodegradable, have been prepared and characterised by gravimetric analysis for moisture uptake, X-ray powder diffraction for crystallinity, and tensile testing for mechanical properties. Results have shown that the addition of bagasse fibre (5 wt%, 10 wt% or 20 wt%) to either (modified) potato starch (Soluble starch) or hydroxypropylated maize starch reduced moisture uptake by up to 30% at 58% relative humidity (RH). Also, the tensile strength and the Young’s Modulus increased up to 63% and 80% respectively, with the maximum value obtained with 5 wt% fibre at 58% RH. However, the tensile strain of the films significantly decreased by up to 84%. The results have been explained based on the crystallinity of the films and the intrinsic properties of starch and bagasse fibres.

Alumino-silicate derivatives

The formation of new materials in the form of alumino-silicate derivatives from 2:1 layer clay materials which are obtained by the chemical modification of 2:1 layer clay minerals by reaction with a salt having the formula MX wherein M is ammonium ion or alkali metal cation and X is a halide. The new materials have the following characteristics: (a) an amorphous x-ray diffraction signal manifest as a broad hump using x-ray powder diffraction between 22.degree. and 32.degree. 2.theta. using CuK.alpha. radiation; and (b) the presence of primarily tetrahedrally coordinated aluminum.

Stichtite : a review

Stichtite is a naturally occurring layered double hydroxide (LDH) with the ideal chemical formula Mg6Cr2CO3(OH)16·4H2O. It has received less attention in the literature than other LDHs and is often described as a rare mineral; however, abundant deposits of the mineral do exist. In this article we aim to review a number of significant publications concerning the mineral stichtite, including papers covering the discovery, geological origin, synthesis and characterizsation of stichtite. Characterization techniques reviewed include powder X-ray diffraction (XRD), infrared spectroscopy (IR), near infrared spectroscopy (NIR), Raman spectroscopy (Raman), thermogravimetry (TG) and electron microprobe analysis.

Electrochemically-induced TCNQ/Mn TCNQ 2 (H2O) 2 (TCNQ= 7, 7, 8, 8-Tetracyanoquinodimethane) solid-solid interconversion : two voltammetrically distinct processes that allow selective generation of nanofiber or nanorod network morphologies

Unlike the case with other divalent transition metal M\[TCNQ](2)(H(2)O)(2) (M = Fe, Co, Ni) analogues, the electrochemically induced solid-solid phase interconversion of TCNQ microcrystals (TCNQ = 7,7,8,8-tetracyanoquinodimethane) to Mn\[TCNQ](2)(H(2)O)(2) occurs via two voltammetrically distinct, time dependent processes that generate the coordination polymer in nanofiber or rod-like morphologies. Careful manipulation of the voltammetric scan rate, electrolysis time, Mn(2+)((aq)) concentration, and the method of electrode modification with solid TCNQ allows selective generation of either morphology. Detailed ex situ spectroscopic (IR, Raman), scanning electron microscopy (SEM), and X-ray powder diffraction (XRD) characterization clearly establish that differences in the electrochemically synthesized Mn-TCNQ material are confined to morphology. Generation of the nanofiber form is proposed to take place rapidly via formation and reduction of a Mn-stabilized anionic dimer intermediate, \[(Mn(2+))(TCNQ-TCNQ)(2)(*-)], formed as a result of radical-substrate coupling between TCNQ(*-) and neutral TCNQ, accompanied by ingress of Mn(2+) ions from the aqueous solution at the triple phase TCNQ/electrode/electrolyte boundary. In contrast, formation of the nanorod form is much slower and is postulated to arise from disproportionation of the \[(Mn(2+))(TCNQ-TCNQ)(*-)(2)] intermediate. Thus, identification of the time dependent pathways via the solid-solid state electrochemical approach allows the crystal size of the Mn\[TCNQ](2)(H(2)O)(2) material to be tuned and provides new mechanistic insights into the formation of different morphologies.

Mechanism of the α-to-β phase transformation in the LaNi5–H2 system

High-energy synchrotron in situ X-ray powder diffraction has been used to elucidate the mechanism of the hydriding phase transformation in a LaNi5 model hydrogen storage intermetallic in real time. The transformation proceeds at 10 °C via the transient growth of an interfacial phase, the γ phase, with lattice parameters intermediate between those of the α (dilute solid solution) and β (concentrated hydride) phases. The γ phase forms to partially accommodate the 24% change in unit cell volume between the α and β phases during hydriding and dehydriding. The α, γ and β phases coexist at the nanoscopic level.