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Motivated by the need of new red phosphor for white - light - emitting diodes (WLEDs) application, Eu3+ doped Sc2-xInx(WO4)3 (x = 0, 1, 2) solid solutions were synthesized by high temperature solid - state reaction. Structural and luminescent properties were obtained by using X - ray diffraction (XRD), infrared and photoluminescence spectroscopic techniques. IR spectrum of the ScIn(WO4)3 doped with Eu3+ contains the characteristic vibrations of the WO4 and MeO6, (Me = Sc, In) polyhedral, building the Sc2(WO4)3 and In2(WO4)3 structures. An effective energy transfer from the tungstate matrix to the active Eu3+ ion was observed. Intense red luminescence was obtained in these samples under excitation at 394 nm using the sharp 7F0 → 5L6 transition of Eu3+. The calculated asymmetric ratio (5D0 → 7F2 / 5D0 → 7F1) was about 7.5, suggesting that the obtained materials are characterized with distorted environment around the rare earth ion and with high red emission intensity. The prepared ScIn(WO4)3 solid solution demonstrates the highest emission intensity. The obtained chromaticity coordinates of the Eu3+ doped Sc2-xInx(WO4)3 solid solutions were very close to the red standard recommended by National Television Standards Committee (NTSC). [ABSTRACT FROM AUTHOR]

CaWO4 nanoparticles were obtained by facile mechanochemical synthesis at room temperature, applying two different milling speeds. Additionally, a solid-state reaction was employed to assess the phase composition, structural, and optical characteristics of CaWO4. The samples were analyzed by X-ray diffraction (XRD), transition electron microscopy (TEM), and Raman, infrared (IR), ultraviolet–visible (UV–Vis) reflectance, and photoluminescence (PL) spectroscopies. The phase formation of CaWO4 was achieved after 1 and 5 h of applied milling speeds of 850 and 500 rpm, respectively. CaWO4 was also obtained after heat treatment at 900 °C for 12 h. TEM and X-ray analyses were used to calculate the average crystallite and grain size. The Raman and infrared spectroscopies revealed the main vibrations of the WO4 groups and indicated that more distorted structural units were formed when the compound was synthesized by the solid-state method. The calculated value of the optical band gap of CaWO4 significantly increased from 2.67 eV to 4.53 eV at lower and higher milling speeds, respectively. The determined optical band gap of CaWO4, prepared by a solid-state reaction, was 5.36 eV. Blue emission at 425 (422) nm was observed for all samples under an excitation wavelength of 230 nm. CaWO4 synthesized by the solid-state method had the highest emission intensity. It was established that the intensity of the PL peak depended on two factors: the morphology of the particles and the crystallite sizes. The calculated color coordinates of the CaWO4 samples were located in the blue region of the CIE diagram. This work demonstrates that materials with optical properties can be obtained simply and affordably using the mechanochemical method. [ABSTRACT FROM AUTHOR]

In this paper, the crystallization behavior of 50ZnO:47B2O3:3Nb2O3:0.5Eu2O3 (G-0 h) glass has been investigated in detail by DSC, XRD and TEM analysis. The luminescent properties of the resulting glass-ceramics were also investigated. By XRD and TEM analysis, crystallization of several crystalline phases has been proved (α-Zn3B2O6, β-Zn3B2O6 and ZnNb2O6). By calculating crystal parameters, it was found that europium ions are successfully incorporated in the β-Zn3B2O6. Photo-luminescent spectra showed increased emission in the resulting glass-ceramic samples compared to the parent glass sample due to higher asymmetry of Eu3+ ions in the obtained crystalline phases. It was established that the optimum emission intensity is registered for glass-ceramic samples obtained after 25 h heat treatment of the parent glass. [ABSTRACT FROM AUTHOR]

Inspired by our finding that metallic Ni particles could be uniformly distributed on a reduced CeO2 surface and stabilized on Ce3+ sites, we suppose a possible improvement in the activity and selectivity of the MgNi/SiO2 vegetable oil hydrogenation catalyst by increasing the surface metal Ni availability via modification by ceria. The proposed approach involved the addition of a CeO2 modifier to the SiO2 carrier and as a catalyst component. Evaluation of the structure, reducibility, and surface and electronic states of the CeO2-doped MgNi/SiO2 catalyst was performed by means of the Powder X-ray diffraction (PXRD), Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS) combined with High-resolution transmission electron microscopy (HRTEM), Temperature-programmed reduction with hydrogen (H2-TPR), and H2-chemisortion techniques. So far, no studies related to this approach of designing Ni/SiO2 catalysts for the partial hydrogenation of vegetable oil have been reported. The added ceria impact was elucidated by comparing fatty acid compositions obtained by the catalysts at an iodine value of 80. In summary, tuning the hydrogenation performance of Ni-based catalysts can be achieved by structural reconstruction using 1 wt.% CeO2. The introduction mode changed the selectivity towards C18:1-cis and C18:0 fatty acids by applying ceria as a carrier modifier, while hydrogenation activity was improved upon ceria operation as the catalyst dopant. [ABSTRACT FROM AUTHOR]

Sand-rose shaped β-Ni(OH)2 submicron particles were successfully synthesized by a simple wet-chemistry process. The influence of the as-prepared material on the thermal decomposition of ammonium perchlorate (AP) was explored by thermogravimetry and differential scanning calorimetry analyses. The in-situ formation of active NiO species in the AP/β-Ni(OH)2 system is beneficial for electron transfer in the decomposition steps of AP, leading to the acceleration of its thermal decomposition. In particular, the addition of 5 wt. % β-Ni(OH)2 to AP lowers the decomposition temperature of the latter by 68.5°C and, moreover, the apparent heat of decomposition is increased almost twofold compared to that of pure AP. [ABSTRACT FROM AUTHOR]

In this work, a novel approach is suggested to grow bilayer fibers by combining electrospinning and atomic layer deposition (ALD). Polyvinyl alcohol (PVA) fibers are obtained by electrospinning and subsequently covered with thin Al2O3 deposited at a low temperature by ALD. To burn the PVA core, the fibrous structures are subjected to high-temperature annealing. Differential scanning calorimetry (DSC) analysis of the PVA mat is performed to establish the proper annealing regime for burning off the PVA core and obtaining hollow fibers. The hollow fibers thus formed are covered with a ZnO layer deposited by ALD at a higher temperature within the ALD window of ZnO. This procedure allows us to prepare ZnO films with better crystallinity and stoichiometry. Different characterization methods—SEM, ellipsometry, XRD, and XPS—are performed at each step to investigate the processes in detail. [ABSTRACT FROM AUTHOR]

The hydrogen sorption of materials based on 80 wt.% MgH2 with the addition of 15 wt.% Ni or V and 5 wt.% activated carbons synthesized from polyolefin wax, a waste product from polyethylene production (POW), walnut shells (CAN), and peach stones (CPS) prepared by milling under an inert Ar atmosphere for a period of 1 h, is investigated. All precursors are submitted to pyrolysis followed by steam activation in order to obtain the activated carbons. The hydrogen sorption evaluations are carried out for absorption at 473 and 573 K with pressure of 1 MPa and for desorption at 623 and 573 K with pressure of 0.15 MPa. The composition of the samples after milling and hydrogenation is monitored by X-ray diffraction analyses. The 80 wt.% MgH2–15 wt. %Ni–5 wt.% POW or CAN after absorption–desorption cycling and in a hydrogenated state at 573 K and 1 MPa are analyzed by TEM. [ABSTRACT FROM AUTHOR]

Powder samples of Li2CaGeO4, Ca2GeO4, and Ca5Ge3O11 doped by 0.5, 1, 2, 3, 4 and 5 at% Eu3+ relative to the Ca2+, were prepared using a conventional solid‐state synthesis technique. X‐ray diffraction (XRD) analyses confirmed obtaining the pure phases at all dopant concentrations. In parallel, single crystals of the three compounds with the experimentally found optimal Eu3+ concentration were grown using a flux method. Structural investigation on the single crystals were done with a special attention to the form of the Ca–O polyhedron, the mean Ca–O distance, the Ca–Ca distance in the structure, the distortion degree of the polyhedron, as well as the Eu–Ca substitution site. The main spectral characteristics were analyzed and several relationships between the structural and spectra features were found. The optimal dopant concentration was 3 at% for Ca2GeO4 and 4at% for Ca5Ge3O11 and Li2CaGeO4. Commission Internationale de l'éclairage coordinates of the samples showed emission colours in the red region close to the standard red coordinates and slightly influenced by the active ion concentration. The obtained results showed that europium‐doped Li2CaGeO4, Ca2GeO4, and Ca5Ge3O11 could be used as red phosphors. [ABSTRACT FROM AUTHOR]

The effect of nickel content on the structure and activity of co-precipitated Ni–Al layered double hydroxides (LDHs) as catalyst precursors for CO 2 removal by methanation was studied by variation of the Ni 2+/Al 3+ molar ratio (Ni 2+/Al 3+ = 3.0, 1.5 and 0.5), and of the reduction and reaction temperatures as well as of the space velocities. Powder X-ray diffraction (PXRD), H 2 chemisorption, and temperature programmed reduction (TPR) techniques were applied for physicochemical characterization of the samples. It was specified that the nano-scaled dimensions of the as-synthesized samples also generate nano-metrical metallic nickel particles (PXRD). The existence of readily and hardly reducible Ni 2+–O species in the studied samples (TPR), affects catalytic performance. The studied catalysts hydrogenate CO 2 effectively to residual concentrations of the latter in the range of 0–10 ppm at reaction temperatures from 400 to 220 °C and space velocities between 22,000 and 3000 h −1. The variation of the CO 2 methanation activity with the changes of space velocities depends on the nickel content, and reduction and reaction temperatures. After reduction at 400 and 450 °C, a sample of Ni 2+/Al 3+ = 3.0 has demonstrated the highest conversion degree at all the reaction temperatures and space velocities, while a catalyst of Ni 2+/Al 3+ = 0.5 dominated in the methanation activity after reduction within 530–600 °C. The Ni 2+/Al 3+ = 1.5 catalyst data take intermediate position between Ni 2+/Al 3+ = 3.0 and Ni 2+/Al 3+ = 0.5 often closer to Ni 2+/Al 3+ = 3.0 ones. The studied Ni–Al LDH systems are found to be promising catalyst precursors for fine CO 2 removal from hydrogen-rich gas streams through the methanation reaction, depending on the technological regime of catalyst activation. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper we report the combustive synthesis of a series of polycrystalline compounds with the general formula Pb1.33Sr0.67−x Ba x Fe2O5 (0≤ x ≤0.67). They belong to a new class of materials derived from perovskite by crystallographic shear planes, which changes the iron coordination from corner-shared octahedra to edge-shared trigonal bipyramids at the shear planes. These materials are considered to be prospective candidates for multiferroics. The samples were characterized by thermal analysis (TG-DTA), X-ray diffraction and scanning electron microscopy. The crystal structure parameters were refined using the TOPAS 3 program. The observed structural changes were related to the substitution of Sr2+ by Ba2+ within a limited part of the structure. It may be concluded that the “inflation” of the perovskite blocks provoke corresponding changes within the double-chain layers. As a result, the structure appears to be very flexible and adaptive towards cation substitutions. [Copyright &y& Elsevier]

BiFeO3 is an interesting material due to its multiferroic properties. It attracts attention due to its potential applications in spintronics and in microelectronics for data storage, among others. Single-phase bulk material from BiFeO3 is difficult to synthesize. The kinetics of perovskite phase formation most often leads to the presence of impurity phases. It has been shown that low levels of replacement of Bi with rare earth ions lead to stabilization of the perovskite phase. In the present work, Rietveld refinement of the crystal structure based on powder X-ray diffraction patterns was applied to study the influence of partial substitution of Bi by rare-earth (RE) elements with different ionic radii on structural and morphological properties of the ferrite phase. Substitution by large RE ions was found to preserve the rhombohedral symmetry of BiFeO3, whereas substitution by smaller RE ions led to the coexistence of two polymorphic perovskite phases with rhombohedral R3c and orthorhombic Pnma symmetries. The unit cell parameters as well as the interatomic distances and angles, not only around the A cation but also around the iron ions, were influenced by the substitution. The mean crystallite and particle size decreased with the decrease of ionic radius of substituting RE ion. [ABSTRACT FROM AUTHOR]