Powder Spectra Research Articles

Application of the Mössbauer effect to the study of subnanometer harmonic displacements in thin solids

We measure subnanometer displacements of thin samples vibrated by piezotransducer. Samples contain $^{57}$Fe nuclei, which are exposed to 14.4 keV $\gamma$-radiation. Vibration produces sidebands from a single absorption line of the sample. The sideband intensities depend on the vibration amplitude and its distribution along the sample. We developed a model of this distribution, which adequately describes the spectra of powder and stainless steel (SS) absorbers. We propose to filter $\gamma$-radiation through a small hole in the mask, placed before the absorber. In this case only a small spot of the vibrated absorber is observed. We found for SS foil that nuclei, exposed to $\gamma$-radiation in this small spot, vibrate with almost the same amplitudes whose difference does not exceed a few picometers.

Spin-gapped Mott insulator with the dimeric arrangement of twisted molecules Zn(tmdt) 2

$^{13}$C nuclear magnetic resonance measurements were performed for a single-component molecular material Zn(tmdt)$_{2}$, in which tmdt's form an arrangement similar to the so-called ${\kappa}$-type molecular packing in quasi-two-dimensional Mott insulators and superconductors. Detailed analysis of the powder spectra uncovered local spin susceptibility in the tmdt ${\pi}$ orbitals. The obtained shift and relaxation rate revealed the singlet-triplet excitations of the ${\pi}$ spins, indicating that Zn(tmdt)$_{2}$ is a spin-gapped Mott insulator with exceptionally large electron correlations compared to conventional molecular Mott systems.

Mössbauer and XRD characterization of the effect of heat treatment and the tribological test on the physical and mechanical properties of a Fe-Mn-Al-C alloy

In this study, a Fe-29.0Mn-6.0Al–0.9C-1.8Mo-1.6Si-0.4Cu (Wt. %) alloy was prepared in an induction furnace. The as-cast sample was submitted to homogenization at 1050 °C over 8 hours, which was followed by quenching, and an aging heat treatment at 500 °C for 12 h. Wear tests were performed by using a Pin on Disk Tribometer (ASTM G99) at room temperature to evaluate the mass loss. Optical Microscopy, X-Ray Diffraction, and Transmission Mossbauer Spectroscopy were used to characterize the microstructure and structural properties of the samples. The obtained microstructure of the heat-treated samples was of the austenitic type, and their XRD patterns were refined with the lines of the austenite, martensite, galaxite, and FeO structures. Mossbauer spectra of powders, obtained from the surface of the samples, showed the presence of a broad doublet, which corresponded to the disordered austenite; and a small hyperfine magnetic field distribution associated with the disordered and ferromagnetic martensite. After the tribology test, the surface of the sample was examined, and it was obderved that the austenite, martensite, and galaxite phases were present. The martensite quantity increased and, those of galaxite and austenite decreased, but that of austenite appeared to have larger lattice parameter. The decrease in the galaxite content was a direct consequence of the wear test, which removed matter from the sample surface. The appearance of additional martensite was due to the transformation of the austenite by mechanical work. The additional presence of a new austenite with a bigger lattice parameter and of the Fe oxide was the consequence of the heating process of the sample during the tribological test. The Mossbauer spectrum of this sample confirms the increase of the martensite content. The mechanical properties increased with the heat treatment.

A comparative study on the experimental and calculated results of mid-infrared and Raman vibrational modes of nucleic acid bases

The MIR (mid-infrared) and Raman spectra of the nucleic acid base powders were tested by Fourier transform infrared spectroscopy and laser Raman spectroscopy. The vibrational modes of nucleic acid base crystals were simulated by the generalized energy-based fragmentation approach under periodic boundary conditions (hereinafter referred as PBC-GEBF) together with Guassian09 software. Taking into account the intermolecular hydrogen bonds in the unit cell and the weak interactions between the unit cells, the PBC-GEBF method adopted by our group was for the first time used for calculating nucleic acid base crystals in the 400–2000cm−1 band. The theoretical and experimental spectra turn out to be in good agreement with each other. Compared with the calculated results of the nucleic acid base monomer, the calculated results of crystals appear to be in better agreement with the experimental results. Some weak vibration peaks were reproduced by simulation, and the positions of the vibration peaks agree well. By analyzing the vibrational modes, it can be observed that the vibrational modes below 1000 cm−1 are mainly characterized by the collective vibrations involving all the molecules in the unit cell. In addition to intramolecular interactions, weak intermolecular interactions (including Van der Waals force and weak hydrogen bond) and the lattice stacking force also contribute to the overall vibrations. This study is of great importance to the analysis of the stability of RNA/DNA structures and their genetic properties.

Radiation stability of TiO2 hollow particles pigments and coatings synthesis by hydrothermal methods from TTIP

The effect of protons (E = 100 keV and F = 5 × 1015 cm−2) exposure on the diffuse reflectance spectra of the TiO2 hollow particles powders and coatings based on them in wavelength range from 250 to 2500 nm have been investigated. The synthesis of the hollow particles was carried out by the hydrothermal method using chemicals TTIP and TBAH. The coatings were prepared from a mixture of hollow particles and organosilicon binder (polydimethylsiloxane). Evaluating the changes of the solar absorptance it was found that the radiation stability of the TiO2 hollow particles and coatings based on them is higher than the radiation stability of the powder and coatings based on microparticles. The low radiation stability of the hollow particles is due to a decrease in the concentration of radiation-induced defects.

Preparation and characterization of thulium doped yttrium oxide (Tm:Y 2 O 3 ) powders

Abstract In the presented work 2 at% thulium doped yttrium oxide precursor powders were synthesized by the co-precipitation method using ammonium bicarbonate as a precipitation agent. The main aim of this work was to investigate the influence of co-precipitation parameters such as the process temperature (25°C–70 °C) and molar concentration of reagents on the morphology and luminescence properties of Tm:Y 2 O 3 . The lowest average particle size of about 20 nm and the highest value of the specific surface of 55.2 m 2 /g were obtained for powder co-precipitated at a temperature of 70 °C at a molar concentration of 0.1 M for thulium and yttrium nitrate. The emission spectra of the outcome powders were measured and compared and fluorescence dynamics behavior was presented and discussed.

Assessing sulfur redox state and distribution in abyssal serpentinites using XANES spectroscopy

Sulfur is one of the main redox sensitive and volatile elements involved in chemical transfers between earth surface and the deep mantle. At mid-oceanic ridges, sulfur cycle is highly influenced by serpentinite formation which acts as a sink of sulfur under various oxidation states (S2−, S−, S0 and S6+). Sulfur sequestration in serpentinites is usually attributed to the crystallization of secondary minerals, such as sulfides (e.g. pyrite, pyrrhotite) or sulfates (e.g. anhydrite). However, the role of serpentine minerals as potential sulfur carriers is not constrained. We investigate the distribution and redox state of sulfur at micro-scale combining in situ spectroscopic (X-ray absorption near-edge structure: XANES) and geochemical (SIMS) measurements in abyssal serpentinites from the SWIR (South West Indian Ridge), the Rainbow and the MARK (Mid-Atlantic Ridge, Kane Fracture Zone) areas. These serpentinites are formed in different tectono-metamorphic settings and provide a meaningful database to understand the fate of sulfur during seafloor serpentinization. XANES spectra of serpentinite powders show that the sulfur budget of the studied samples is dominated by oxidized sulfur (S6+/∑S=0.6–1) although sulfate micro-phases, such as barite and anhydrite, are absent. Indeed, μ-XANES analyses of mesh, bastite and antigorite veins in thin sections and of serpentine grains rather suggest the presence of S6+ ions incorporated into serpentine minerals. The structural incorporation of S in serpentine minerals is also supported by X-ray fluorescence mapping revealing large areas (1600 μm2) of serpentinite where S is homogeneously distributed. Our observations show that serpentine minerals can incorporate high S concentrations, from 140 to 1350 ppm, and that this can account for 60 to 100% of the sulfur budget of abyssal serpentinites. Serpentine minerals thus play an important role in S exchanges between the hydrosphere and the mantle at mid-oceanic ridges and may participate to S recycling in subduction zones.

Probing the interaction of the potassium channel modulating KCNE1 in lipid bilayers via solid-state NMR spectroscopy.

KCNE1 is known to modulate the voltage-gated potassium channel α subunit KCNQ1 to generate slowly activating potassium currents. This potassium channel is essential for the cardiac action potential that mediates a heartbeat as well as the potassium ion homeostasis in the inner ear. Therefore, it is important to know the structure and dynamics of KCNE1 to better understand its modulatory role. Previously, the Sanders group solved the three-dimensional structure of KCNE1 in LMPG micelles, which yielded a better understanding of this KCNQ1/KCNE1 channel activity. However, research in the Lorigan group showed different structural properties of KCNE1 when incorporated into POPC/POPG lipid bilayers as opposed to LMPG micelles. It is hence necessary to study the structure of KCNE1 in a more native-like environment such as multi-lamellar vesicles. In this study, the dynamics of lipid bilayers upon incorporation of the membrane protein KCNE1 were investigated using 31 P solid-state nuclear magnetic resonance (NMR) spectroscopy. Specifically, the protein/lipid interaction was studied at varying molar ratios of protein to lipid content. The static 31 P NMR and T1 relaxation time were investigated. The 31 P NMR powder spectra indicated significant perturbations of KCNE1 on the phospholipid headgroups of multi-lamellar vesicles as shown from the changes in the 31 P spectral line shape and the chemical shift anisotropy line width. 31 P T1 relaxation times were shown to be reversely proportional to the molar ratios of KCNE1 incorporated. The 31 P NMR data clearly indicate that KCNE1 interacts with the membrane. Copyright © 2017 John Wiley & Sons, Ltd.

Nonclassical dynamics of the methyl group in 1,1,1-triphenylethane. Evidence from powder 1H NMR spectra.

According to the damped quantum rotation (DQR) theory, hindered rotation of methyl groups, evidenced in nuclear magnetic resonance (NMR) line shapes, is a nonclassical process. It comprises a number of quantum-rate processes measured by two different quantum-rate constants. The classical jump model employing only one rate constant is reproduced if these quantum constants happen to be equal. The values of their ratio, or the nonclassicallity coefficient, determined hitherto from NMR spectra of single crystals and solutions range from about 1.20 to 1.30 in the latter case to above 5.0 in the former, with the value of 1 corresponding to the jump model. Presently, first systematic investigations of the DQR effects in wide-line NMR spectra of a powder sample are reported. For 1,1,1-triphenylethane deuterated in the aromatic positions, the relevant line-shape effects were monitored in the range 99-121 K. The values of the nonclassicality coefficient dropping from 2.7 to 1.7 were evaluated in line shape fits to the experimental powder spectra from the range 99-108 K. At these temperatures, the fits with the conventional line-shape model are visibly inferior to the DQR fits. Using a theoretical model reported earlier, a semiquantitative interpretation of the DQR parameters evaluated from the spectra is given. It is shown that the DQR effects as such can be detected in wide-line NMR spectra of powdered samples, which are relatively facile to measure. However, a fully quantitative picture of these effects can only be obtained from the much more demanding experiments on single crystals.

Red-brown ceramic pigments based on chromium doped ferrian armalcolite, effect of mineralizers

A new red-brown ceramic pigment based on chromium-doped ferrian armalcolite have been synthesized and characterized. (MgFe)(CrxTi3−xFe)O10 powders (x=0–0.3) fired at 1200°C crystallize ferrian armalcolite as the only crystalline phase detected. Samples fired at 1000°C show red-brown shades in glazes that darken and bluish (b* turns to negative values) at 1200°C. The x=0.2 sample fired at 1000°C shows the best red colour (L*a*b*=49.5/15.2/10.3). Assignment of bands in the UV–Vis–NIR spectra is difficult due to the overlapping of Cr3+, Cr4+ and Fe3+ absorptions in octahedral coordination. Analysis of UV–Vis–NIR spectra of powders shows that these spectra are dominated by the strong absorption associated to Fe3+ ions in octahedral sites. In contrast, an intense band at 520nm dominates the UV–Vis–NIR spectra of glazed samples, which should be associated to Cr4+ in octahedral coordination. This absorption increases when the amount of chromium increases, indicating that chromium is the real chromophore of the system. Finally, the weak shoulder at 600nm and the double weak band at 700nm, detected more evidently when chromium amount in sample increases, indicate the progressive presence of Cr3+ in octahedral sites. The entrance of Cr4+ in x=0.1 sample shrinks the crystalline cell, but when chromium amount in the samples increases, both Cr4+ and Cr3+enter simultaneously and the unit cell remains practically stable. The microstructure of the powders analysed by SEM microscopy indicates aggregates of 6–10 fine particles of 200–400nm of diameter. The addition of mineralizers (boric acid, sodium perborate, NaF and a mixture BaF2.4MgF2) does not modify significantly the reactivity of the system; at 1000°C hematite and rutile remain as residual crystalline phases, except in NaF additions where the crystallization of NaFeTi3O8 is detected. SEM-EDX mapping analyses of pigment powders confirm in all cases a homogeneous distribution of ions in the particles.

Vibrational Spectroscopy of Binary Titanium Borides: First-Principles and Experimental Studies

Vibrational dynamics of binary titanium borides is studied from first-principles. Polarized and unpolarized Raman spectra of TiB, TiB2, and Ti3B4 are reported along with the experimental spectra of commercial powder and bulk TiB2 containing less than 1 wt.% of impurity phases. The X-ray diffraction spectroscopy, applied for phase composition examination of both bulk and powder materials, identifies only the TiB2 phase. The simulated Raman spectra together with literature data support interpretation and refinement of experimental spectra which reveal components arising from titanium dioxide (TiO2) and amorphous boron carbide (B4C) impurity phases as well as graphitic carbon. These contaminations are the by-products of synthesis, consolidation, and sintering aids employed to fabricate powder and bulk titanium diboride.

Enhanced visible light absorption and reduced charge recombination in AgNP plasmonic photoelectrochemical cell

In this research work, silver nanoparticles (AgNP) were synthesized using a simple solvothermal technique, the obtained AgNP were used to prepare a titania/silver (TiO2/Ag) nanocomposites with varied amount of Ag contents and used to fabricated a photoanode of dye-sensitized solar cell (DSSC). X-ray photoelectron spectroscopy (XPS) was used to ascertain the presence of silver in the nanocomposite. A photoluminance (PL) spectra of the nanocomposite powder shows a low PL activity which indicates a reduced election- hole recombination within the material. UV–vis spectra reveal that the Ag in the DSSC photoanode enhances the light absorption of the solar cell device within the visible range between λ=382nm and 558nmnm owing to its surface plasmon resonance effect. Power conversion efficiency was enhanced from 4.40% for the pure TiO2 photoanode based device to 6.56% for the device fabricated with TiO2/Ag due to the improvement of light harvesting caused by the localized surface plasmonic resonance effect of AgNP. The improvement of power conversion was also achieved due to the reduced charge recombination within the photoanode.

Conformer of the peroxynitrite ion formed under photolysis of crystalline alkali nitrates – cis or trans?

The optical and infrared reflectance spectra of the crystalline powders prepared by co-crystallization of caesium nitrate, nitrite, and peroxynitrite from alkali solution have been studied. We find that the trans conformer forms under photolysis of crystalline pure caesium nitrate. Under its dissolution the trans conformer transforms to the cis conformer.

Synthesis, characterization, electrical and luminescence performance of novel copolymer of anthracene/pyrrole

A novel copolymer of anthracene/pyrrole at their different mole ratios has been prepared by facile oxidative coupling of anthracene and pyrrole using FeCl3 as a catalyst in nitrobenzene/n-hexane. The prepared copolymers were analyzed by using FTIR, 1HNMR, XRD, GPC and thermogravimetric techniques. The SEM photographs of copolymers exhibit uniform morphology and their crystallites arranged with random orientations. The temperature dependent electrical conductivity of copolymers was changed with respect to pyrrole concentration. The observed red shift in UV–Visible and excitation spectra of copolymers with pyrrole contents indicates the formation of large conjugation in their main chain. The fluorescence spectra of solid powder of copolymers was observed in the green region at maximum wavelength 518 nm with the addition of anthracene contents. However, the copolymer in the solution of concentrated sulphuric acid exhibited tuning of emission towards the red side. Furthermore, the copolymer excited at the maximum absorption wavelength (340 nm) of the pyrrole shows same emission band, indicating efficient energy transfer between pyrrole and anthracene units. Therefore, the present study shows improved thermal, electrical and optical properties of copolymers, which have practical applications in the fields of optoelectronic devices such as organic light emitting diode, conducting devices, solar cells etc.

Factors controlling the thermoluminescence spectra of rare earth doped calcium fluoride

Thermoluminescence spectra of rare earth doped calcium fluoride samples, both powder and single crystal, were recorded over the temperature range from 25K to 673K. Although some broad band features exist, the spectra are dominated by the rare earth line transitions. The glow peak temperatures are slightly sensitive both to the ionic size of the dopants and the dopant concentration. By contrast, very considerable differences are generated by heat treatments, such as annealing followed by either fast or slow cooling. Comments are included on the reasons for such sensitivity in terms of association of dopant and intrinsic defect sites and why the results of dosimetry powder differ from those from single crystals.

Synthesis, structure and physicochemical characterization of the hybrid material [C6H16N2O]2 SnCl6·2Cl·2H2O

The current study reports the chemical preparation, crystal structure, Hirshfeld surface analysis and spectroscopic characterization of the novel compound [C6H16N2O]2SnCl6·2Cl·2H2O. This compound crystallizes in the triclinic system (space group P − 1, Z = 1) with the following unit cell dimensions: a = 7.9764(9), b = 8.2703(9), c = 12.1103(14)Å, α = 84.469(6), β = 75.679(6), and γ = 64.066(5)°. The structure was solved using 3093 independent reflections down to R = 0.020. The atomic arrangement shows alternation of organic and inorganic entities. The cohesion between these entities is ensured by NH…Cl and OH…Cl hydrogen bonds that build a three-dimensional network. The 3D Hirshfeld surfaces and the associated 2D fingerprint plots were investigated for intermolecular interactions. The 13C and 15N CP-MAS NMR spectra are in agreement with the X-ray structure. The vibrational absorption bands were identified by infrared spectroscopy. DFT calculations allowed the attribution of the IR and NMR bands. X-ray powder, XPS and UV spectrum have been carried out. The DSC profile shows that the title material exhibits dehydration at 339 K.

Exciting Wide NMR Spectra of Static Solid Samples with Weak Radiofrequency Fields

Abstract Trains of short pulses in the manner of ‘delays alternating with nutations for tailored excitation’ (DANTE) have been applied to the Pake patterns of protons of water molecules trapped in a static powdered sample of barium chlorate monohydrate. The spin dynamics in the course of such experiments have been investigated by means of numerical simulations and compared with the ideal refocusing that can be achieved under magic-angle spinning (MAS). Solid echoes yield essentially undistorted lineshapes, in contrast to direct excitation without refocusing that leads to severe dispersions of the phases because of inhomogeneous interactions such as homonuclear dipolar couplings and anisotropic chemical shifts. The selectivity of DANTE sequences allows one to access ‘slices’ of the Pake pattern that can be related to particular crystallite orientations. Single-crystal spectra can therefore be extracted from powder spectra. A similar behavior is expected for both dipolar and quadrupolar echoes.

Hydrothermal Synthesis of Flower-Like α-Quartz Nanostructures from Iran Kaolin

Over the past many years, synthesized silica (SiO2) has attracted wide attention because of its unique characteristics, such as low density, low thermal conductivity, high surface area, high thermal shock resistance and high specific strength. In this study, Flower-like α-quartz nano-structures have been synthesized through the hydrothermal method. The synthetic α-quartz powder was obtained using the feedstock of locally kaolin after 15 h. reaction at 180°C. The characterization of the product was investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform InfraRed (FT-IR) spectrometer. The FT-IR spectrum of the nano-crystalline powders confirms the presence of silica. SEM studies have revealed flower-like structures consisting of nano-sheets. In the synthetic quartz, most of the population is of nano-sized and lies between 1 µm to 15 µm. This developed method has many advantages such as synthesis at low temperature and desired pH to yield superior product of desired specification.

Investigating the Influence of Transition Metal Composition on High-Voltage Cathodes Performance By Using Magnetic Susceptibility

High-voltage cathodes are indispensable to enable the high-energy-density batteries. This work demonstrates the effect of Ni/Mn composition on structure of pristine and cycled layered Li-Ni-Mn/Al-Co oxide (NMC and NCA) during high-voltage operation (4.75V vs. Li). Particle morphology and elemental composition of all material was investigated by using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) analysis. Among the various materials NMC622 had the best uniformity in particle size at ~10um while the other materials ranged from ~5-10um. X-ray diffraction (XRD) spectra of the as-obtained powders showed little variation in the structure of layered oxide with different transition metal ion compositions. Temperature dependent magnetic susceptibility results show that NMC622 (with 60% Ni) is layered with less magnetic ordering which was very similar to that of NCA811 (80% Ni) while NMC442 (40% Ni) showed strong magnetic ordering, which suggests exchange of strong magnetic interaction among transition metal ions in NMC442 material. The structural differences that were observed from magnetic susceptibility results were correlated with the electrochemical performance. The detailed pristine structure and structural evolution in layered oxides varying the Ni concentration in the light of magnetic susceptibility will be presented.

Investigation of the spectral–luminescent properties of the threonine molecule

We have investigated the laser-excited photoluminescence spectra of powder and aqueous solution threonine. The spectral ranges of the photoluminescence and its intensity maxima have been determined. We have measured the spectral dependence of the molar extinction coefficient of an aqueous solution of threonine. Using quantum-chemical methods, we have calculated the electron absorption spectrum, the dipole moment, and the distributions of charges on individual atoms of the threonine molecule. The calculated electron absorption spectrum has been compared with experiment.