A computer study of the Raman spectra of the (GaN)<Subscript>129</Subscript>, (SiO<Subscript>2</Subscript>)<Subscript>86</Subscript>, and (GaN)<Subscript>54</Subscript>(SiO<Subscript>2</Subscript>)<Subscript>50</Subscript> nanoparticles

The Raman spectra of the (GaN)₁₂₉, (SiO₂)₈₆, and (GaN)₅₄(SiO₂)₅₀ nanoparticles were calculated using the molecular dynamics method. The spectrum of (SiO₂)₈₆ had three broad bands only, whereas the Raman spectrum of (GaN)₁₂₉ contained a large number of overlapping bands. The form of the Raman spectrum of (GaN)₅₄(SiO₂)₅₀ was determined by the arrangement of the GaN and SiO₂ components in it. The nanoparticle with a GaN nucleus had a continuous fairly smooth spectrum over the frequency range 0 ≤ ω ≤ 600 cm⁻¹, whereas the spectrum of the nanoparticle with a SiO₂ nucleus contained well-defined bands caused by vibrations of groups of atoms of different kinds and atoms of the same kind.     

Inelastic neutron scattering in Zr<Subscript>2</Subscript>NiH<Subscript>1.9</Subscript> and Zr<Subscript>2</Subscript>NiH<Subscript>4.6</Subscript>

In this paper we report the results obtained from inelastic neutron scattering measurements on Zr₂NiH_1.9 and Zr₂NiH_4.6 using triple-axis spectrometer at Dhruva reactor, Trombay. The spectrum up to 35 meV represents largely the lattice modes of Zr and Ni atoms. The vibrational frequencies of hydrogen atoms are expected predominantly at higher energies. The phonon spectra from 35–180 meV were recorded using a Be filter as analyser. In order to analyse the observed neutron spectra, we assume a set of Ein-stein modes due to the hydrogen atoms which are delta functions in energy. These delta functions are broadened by the resolution of the instrument. The vibrational frequencies obtained from the fitting of the observed phonon spectra have been assigned to various tetrahedral sites in both the compounds.     

Bandgap-width correction for luminophores CaMoO<Subscript>4</Subscript> and CaWO<Subscript>4</Subscript>

Submicron-powder luminophores CaMoO₄ and CaWO₄ obtained via solid-phase reactions have been studied using diffuse-reflection (DR) spectroscopy and photoluminescence (PL) spectroscopy. It is found that the diffuse-reflection spectrum in the range of a fundamental absorption edge of <300 nm is distorted by PL overlapping, so that subsequent calculations of optical band gap E _g of luminophores CaMoO₄ and CaWO₄ result in an overestimation of this value. An algorithm for the correct processing of diffuse-reflection spectra is described. It is based on a subtraction of the photoluminescence spectrum in the range of fundamental absorption. The correct E _g values and energy values for the defect levels in the bandgap of CaWO₄ and CaMoO₄ are determined to amount to 4.78, 4.83, and 4.86 ± 0.01 eV and 3.97, 4.07, 4.16 ± 0.01 eV, respectively.     

Photoaccumulating film systems based on TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript> and TiO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript>:V<Subscript>2</Subscript>O<Subscript>5</Subscript> nanoheterostructures

The thin-film photocatalysts TiO₂/MoO₃ and TiO₂/MoO₃:V₂O₅ obtained by a combination of sol–gel and sintering techniques were studied using the photooxidation of probing dyes, EPR spectroscopy, X-ray diffraction analysis, and electron microscopy. It was shown that due to charge accumulation caused by UV irradiation, these photocatalysts retain their oxidative activity and ability for self-sterilization in the dark for a long time after irradiation was terminated (up to 5 h for TiO₂/MoO₃:V₂O₅).     

Raman scattering by Hg<Subscript>2</Subscript>F<Subscript>2</Subscript> polycrystals

The Raman spectra of Hg₂F₂ polycrystals are experimentally measured for the first time. The spectra of Hg₂F₂ are interpreted using X-ray diffraction analysis and group-theoretical treatment. The results obtained are discussed in comparison with the spectra of Hg₂Hal₂ crystals.     

Raman and FTIR spectroscopy study of LiFeTiO<Subscript>4</Subscript> and Li<Subscript>2</Subscript>FeTiO<Subscript>4</Subscript>

We report the Fourier transform infrared (FTIR)–Raman spectroscopy study of spinel Li–Fe–Ti–O oxides viz., LiFeTiO₄ and Li₂FeTiO₄ in order to probe structural details such as type of bonding networks viz., octahedral and tetrahedral, and type of different atomic bonds present in those materials. Both the samples were prepared through solid-state reaction route prior to high-energy ball-milling. All the phases prepared through solid-state reaction and ball-milled were probed using X-ray diffraction, field emission scanning electron microscopy, and FTIR–Raman spectroscopy. X-ray diffraction study indicates spinel phase formation with Fd3m space group symmetry for both LiFeTiO₄ and Li₂FeTiO₄. However, pure phase of Li₂FeTiO₄ was not achieved in these preparation routes, rather mixed phases of Li₂FeTiO₄ and Fe₂TiO₄ were achieved. Field emission scanning electron microscopy (FESEM) analysis indicated porous microstructure for LiFeTiO₄ while more agglomerated microstructure for Li₂FeTiO₄. Ball-milling reduces the grain size partly for both the samples. FTIR–Raman spectroscopy indicates the presence of LiO₄ tetrahedral, LiO₆ and TiO₆ octahedral in the spinel network. Presence of Li–Li–O type bonding was also indicated from spectroscopy analysis. Existence of Fe₂TiO₄ phase with Li₂FeTiO₄ was also identified from both FTIR and Raman spectrum. Effect of ball-milling on the spectrum has been exhibited by broadening and peak shifting the FTIR–Raman spectrum, arising from the enhanced lattice strain and structural disorder.     

Structural Aspects of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Magnetic Nanoparticles According to X-Ray and Neutron Scattering

Structural aspects of powders containing magnetic nanoparticles Fe₃O₄/CoFe₂O₄ with the anticipated “core-shell” structure are considered by means of comparative analysis with individual particles of Fe₃O₄, CoFe₂O₄ in accordance of data obtained from X-ray powder diffraction and small-angle scattering of X-ray (synchrotron) radiation and neutrons. It is shown that magnetic particles in the powders under study have a strong polydispersity and form complex aggregates. Characteristic sizes of the crystallites, as well as a ratio of magnetite to cobalt-ferrite in the composition of the Fe₃O₄/CoFe₂O₄ particles were evaluated from the analysis of the diffraction peaks. Аnalyzing the data on small-angle scattering, the dimensional characteristics of particles and aggregates, as well as the volume fraction of the last ones in the powders, have been obtained. Fractal dimensions of aggregates are determined. A significant difference is observed in the scattering on Fe₃O₄/CoFe₂O₄ particles and the total scattering consisting of partial contributions to scattering on individual magnetite (Fe₃O₄) and cobalt-ferrite (CoFe₂O₄) powders, which does not exclude the formation of the “core-shell” structure.     

Synthesis and electrocatalytic activities of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocubes

In this article, a hydrothermal method was developed to synthesize Co₃O₄ nanocubes using hydrogen peroxide (H₂O₂) as oxidant, Co(NO₃)₂·6H₂O as a cobalt source. The products are characterized in detail by multiform techniques including X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the obtained products are Co₃O₄ nanocubes with size ranging between 20 and 40 nm. The effects of the hydrogen peroxide concentration on the size of the products have been studied. The electrocatalytic activities of H₂O₂ reduction on Co₃O₄ nanocubes in phosphate buffer were also evaluated.     

Li<Superscript>+</Superscript> ion conductivity and transport properties of LiYP<Subscript>2</Subscript>O<Subscript>7</Subscript> compound

A lithium yttrium diphosphate LiYP₂O₇ was prepared by a solid-state reaction method. Rietveld refinement of the X-ray diffraction pattern suggests the formation of the single phase desired compound with monoclinic structure at room temperature. The infrared and Raman spectrum of this compound was interpreted on the basis of P₂O₇ ^4? vibrations. The AC conductivity was measured in the frequency range from 100 to 10⁶ Hz and temperatures between 473 and 673 K using impedance spectroscopy technique. The obtained results were analyzed by fitting the experimental data to the equivalent circuit model. The Cole–Cole diagram determined complex impedance for different temperatures. The angular frequency dependence of the AC conductivity is found to obey Jonscher’s relation. The temperature dependence of σ _AC could be described in terms of Arrhenius relation with two activation energies, 0.87 eV in region I and 1.36 eV in region II. The study of temperature variation of the exponent(s) reveals two conduction models: the AC conduction dependence upon temperature is governed by the correlated barrier hopping (CBH) model in region I (T < 540 K) and non-overlapping small polaron tunneling (NSPT) model in region II (T > 540 K). The near value of activation energies obtained from the equivalent circuit and DC conductivity confirms that the transport is through ion hopping mechanism dominated by the motion of the Li⁺ ion in the structure of the investigated material.     

Solid state synthesis of nonstoichiometric Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> composites as visible-light photocatalyst

Nonstoichiometric Bi₂WO₆ photocatalyst with the composition of Bi_2?+?x WO_6?+?1.5x (?0.25 ≤ x ≤ 1) wa synthesized by a facile solid state reaction method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The Bi_2.5WO_6.75 photocatalyst showed excellent visible-light-driven photocatalytic performance; nearly 100 % of RhB (10 ppm, pH?=?3?~?4) was decomposed within 25 min, which demonstrated that nonstoichiometric semiconductors could be an efficient visible-light-driven photocatalyst.     

Synthesis,characterization, and cell performance of Li<Subscript>0.5</Subscript>FeV<Subscript>1.5</Subscript>O<Subscript>4</Subscript>

A Li_0.5FeV_1.5O₄ sample was synthesized using sol-gel route. The X-ray diffraction study indicates formation of spinel phase (with Fd3m space group) for this sample. LiO₄, LiO₆, and V-O bonds were identified from the Raman spectrum, while LiO₄ and Fe-O bonds were identified from the FTIR spectrum of this sample phase. The FESEM study indicates formation of inhomogeneous grains. The surface area of 74.39 m²/g was estimated from the Brunauer-Emmett-Teller (BET) surface area analysis technique. The cyclic voltammetry study of Li_0.5FeV_1.5O₄ indicates an anodic peak at 2.1 V while a cathodic peak at 1.98 V. The charge-discharge study exhibits two voltage plateaus respectively at 2.1 and at 4 V. Stable electrochemical capacity of 40 mAh/g for Li_0.5FeV_1.5O₄ was found for 30 cycles. The electrochemical impedance spectroscopy study indicates smaller bulk resistance and higher ionic diffusion, i.e., less Warburg impedance for this phase. An energy density of 89 Wh/kg, a power density of 33 W/kg, and a 90% Coulombic efficiency was achieved with relatively good cyclic stability from Li_0.5FeV_1.5O₄.     

Optical phonons in Rb<Subscript>2</Subscript>TeBr<Subscript>6</Subscript> and Cs<Subscript>2</Subscript>TeBr<Subscript>6</Subscript> crystals

Raman scattering in Rb₂TeBr₆ and Cs₂TeBr₆ crystals is studied. The phonon spectra of the crystals are calculated using the factor group method. The number of Raman-active modes, their symmetries, and selection rules are found. Observed Raman spectrum lines are identified with atomic vibration modes of the crystal.     

Effect of thermal strain on structure and polarization fatigue of CSD-derived PbZr<Subscript>0.53</Subscript>Ti<Subscript>0.47</Subscript>O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> hetero-structures

PbZr_0.53Ti_0.47O₃/LaNiO₃ (PZT/LNO) hetero-structures have been successfully deposited on MgO, SrTiO₃, Al₂O₃ and Si substrate by chemical solution routes, respectively. The X-ray diffraction measurements show that out-of-plane lattice parameters of PZT increase as increase of thermal expansion coefficient of substrate. Polarization fatigues of Pt/PZT/LNO capacitors are strongly affected by the thermal strain caused by difference of thermal expansion coefficient between PZT and substrate materials. High fatigue resistance of Pt/PZT/LNO can be obtained by using substrate with similar thermal expansion coefficient as PZT. PACS 77.84.Dy; 78.20.Ci; 81.20.Fw     

Preparation of RE<Subscript>2</Subscript>O<Subscript>2</Subscript>SO<Subscript>4</Subscript> (RE=La,Pr-Lu) microspheres from rare-earth-based infinite coordination polymers

Rare-earth-based infinite coordination polymer (RE-ICP) spheres with diameters ranging from 50 nm to 2 μm have been prepared using meso-2,3-dimercaptosuccinic acid (DMSA) as ligand under hydrothermal conditions. RE₂O₂SO₄ microspheres with similar morphology were obtained by calcining the corresponding RE-ICP spheres. However, as for Ce-ICP and Sc-ICP, CeO₂ and Sc₂O₃ were obtained. The products were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy, laser Raman spectrometry, and energy-dispersive X-ray spectrum. Elemental analysis and inductive coupled plasma atomic emission spectrometer were adopted to study the composition of the Eu-ICP. To explore their potential applications, several samples of the products were selected and their properties were investigated. The Eu-ICP and Eu₂O₂SO₄ microspheres give strong red emissions when excited with a 394-nm ultraviolet light. Furthermore, the Eu-ICP displays a high selectivity for Fe(III). The obtained CeO₂ has a strong absorption in the UV region and the Gd₂O₂SO₄ microspheres show paramagnetic behavior.

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Graphical abstract A series of RE₂O₂SO₄ microspheres were prepared using a coordination polymer precursor method.

     

Structural disorder in the paraelectric phase of the Fe<Subscript>3</Subscript>B<Subscript>7</Subscript>O<Subscript>13</Subscript>Br boracite

A structural model of the cubic paraelectric phase of a Fe₃B₇O₁₃Br crystal belonging to the boracite family has been developed using the data obtained by single-crystal X-ray diffraction with due regard for the results of extended X-ray absorption fine structure (EXAFS) spectroscopy. It has been shown that the best agreement between the data obtained by these two methods is achieved within a model assuming a disorder in the arrangement of both the Fe and Br atoms and a high degree of correlation of their displacements. It has been found that, during the phase transition from the rhombohedral ferroelectric phase to the cubic paraelectric phase, no significant transformation of the structure is observed on a local level. In this case, a change in the macroscopic symmetry occurs predominantly as a result of the variation in the set of possible spatial orientations of stable structural fragments, which is characteristic of order-disorder phase transitions.     

Structure and lattice dynamics of PrFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>: Ab initio calculation

The crystal structure and phonon spectrum of PrFe₃(BO₃)₄ are ab initio calculated in the context of the density functional theory. The ion coordinates in the unit cell of a crystal and the lattice parameters are evaluated from the calculations. The types and frequencies of the fundamental vibrations, as well as the line intensities of the IR spectrum, are determined. The elastic constants of the crystal are calculated. A “seed” frequency of the vibration strongly interacting with the electron excitation on the praseodymium ion is obtained for low-frequency A₂ mode. The calculated results are in agreement with the known experimental data.     

Dilute ferrimagnetism of ilmenites Mn<Subscript>3</Subscript>FeTiSbO<Subscript>9</Subscript> and Mn<Subscript>4</Subscript>FeTi<Subscript>2</Subscript>SbO<Subscript>12</Subscript>

Metastable solid solutions (SS) Mn₃FeTiSbO₉ and Mn₄FeTi₂SbO₁₂ with the ilmenite structure (space group R\(\bar 3\)) have been prepared by quenching at normal conditions. The compositions of the compounds have been justified using EDX spectroscopy and X-ray diffraction. The magnetic properties of SSs have been analyzed by comparison with ferrimagnetic ilmenite Mn₂FeSbO₆ (T_N = 269 K) as a natural mineral and ceramics obtained at high pressure and high temperature. The solid solutions have been characterized as dilute magnetic systems formed as a result of substitution of nonmagnetic cations Ti⁴⁺ for a part of Fe³⁺ and Sb⁵⁺ cations. Mn₃FeTiSbO₉ is considered as a ferromagnetic with T_N = 171 K and Mn₄FeTi₂SbO₁₂ as a magnetic with the concentration of magnetic clusters below the percolation threshold.     

Synthesis,crystal structure,Hirshfeld surface analysis,and vibrational and DFT investigation of [C<Subscript>6</Subscript>H<Subscript>10</Subscript>(NH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>3</Subscript>CuBr<Subscript>4</Subscript>.3Br

Single crystal of a new organic–inorganic hybrid material [C₆H₁₀(NH₃)₂]₃CuBr₄.3Br was synthesized by the slow evaporation method at room temperature and characterized by X-ray diffraction, FTIR, Raman spectroscopy, UV–Vis, dielectric measurements, and Hirschfield surface analysis. The title compound crystallizes in trigonal system \( P\overline{3} \).The crystal packing is governed by the N-H…Br and non-classical C-H…Br hydrogen-bonding interactions between the 1, 2-diamoniumcyclohexane cations, the tetrahedral [CuBr₄]^3? anions, and the isolated ion Br^?. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra, and optical properties of the investigated molecule in the ground state. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The optical properties were investigated by optical absorption and show two bands at 260 and 305 nm.     

Specific features of the electronic structure of the CeCu<Subscript>6</Subscript>, CePd<Subscript>3</Subscript>, CeSi<Subscript>2</Subscript>, and CeF<Subscript>3</Subscript> systems

The electronic structure of cerium systems, the hybridization of 4 f and outer-shell electrons, and the influence of the position of the localized 4 f level with respect to the Fermi level E _F in the conduction band have been investigated. The CeCu₆, CePd₃, CeSi₂, and CeF₃ systems have been studied using X-ray photoelectron spectroscopy. The densities of states have been calculated by the tight-binding linearized muffin-tin orbital method within the atomic sphere approximation, which takes into account the covalent character of bonds and the nonspherical distribution of the electron density. The results obtained from the calculations of the total density of states are in good agreement with the valence band X-ray photoelectron data for the systems under investigation. It has been shown that the differences in the properties of the cerium systems are determined by the specific features of their electronic structure. A strong interatomic interaction is characteristic of heavy-fermion systems.     

Evolution in shapes of a series of (111)-based In<Subscript>2</Subscript>O<Subscript>3</Subscript> particles

In₂O₃ particles with different morphology were controllably synthesized on silicon substrates by thermal evaporation of In grains at 900 °C. The structure and morphology of the In₂O₃ particles were evaluated using X-ray diffraction, and scanning and transmission electron microscopies. The evolution in shapes as the ratio of {100} relative to {111} increases is clearly observed. The photoluminescence spectrum of the obtained In₂O₃ structures exhibits UV emission centered at about 378 nm and wide-band emission covering the green and orange regions with three peaks around 525, 572, and 604 nm. PACS 81.05.Hd; 81.07.Bc; 81.16.-c; 61.46.-w; 81.40.Gh