Structural and compositional analyses of nanocrystalline diamond/β-SiC composite films

Nanocrystalline diamond/β-SiC composite films are synthesized by microwave plasma chemical vapor deposition using a gas mixture of H₂, CH₄, and tetramethylsilane (Si(CH₃)₄, TMS) in a single process step. Structural and compositional analyses revealed that the films consist of a mixture of diamond and β-SiC nanocrystalline phases in a desired volume fraction combinatorial form. Transmission electron microscopy analysis confirmed the X-ray diffraction results and showed that the major diffraction lines corresponded to a two-component nanocrystalline composite film. Infrared spectroscopic analysis showed that the content of β-SiC in the films can be increased by increasing the TMS concentration. This correlated very well with electron probe microanalysis and Rutherford backscattering analysis that showed an almost linear correspondence of β-SiC content in the films with the TMS concentration in the gas phase. The phase purity of the diamond crystallites decreased with increase in the β-SiC content in the films, as shown by micro Raman scattering studies. Smooth surface morphologies are measured for these films by using atomic force microscopy; the root mean square roughness was 12 ± 1 nm. The β-SiC volume fraction (vol. %) was identified as an important compositional factor to determine any mechanical and frictional properties of these films. PACS 68.55.-a; 68.55.Nq; 68.60.-p     

Terfenol-D/Pb(Zr,Ti)O3 Disk-Ring Multiferroic Heterostructures Coupled Through Normal Stresses

Disk-ring multiferroic heterostructures composed of Terfenol-D and Pb(Zr,Ti)O₃ (PZT) were prepared and characterized, for which the ferromagnetic and ferroelectric phases were coupled through normal stresses instead of the shear stresses that acted in most of the previous multiferroic heterostructures. High low-frequency magnetoelectric coefficients of 0.10–0.75 V cm⁻¹ Oe⁻¹ were attained for the disk-ring heterostructures, which indicated the strong magnetoelectric coupling. Moreover, a symmetrical resonant peak was observed for dE ₃/dH ₃ in the frequency range of 1–200 kHz, while another weak peak with asymmetrical shape also existed at a lower frequency for dE ₃/dH ₁, which was due to the combination of two vibration modes.     

Synthesis and characterization of Bi-doped zirconia for solid electrolyte

(100-x)ZrO₂(x)Bi₂O₃ (x = 5, 10, 15) system has been synthesized by solid-state reaction technique. Tetragonal Bi_7.38Zr_0.62O_12.31 phase has formed in all the samples after sintering at 850 °C for 24 h. Apart from this, ZrO₂ and Bi₂O₃ are also identified as minority phases. The volume fraction of Bi_7.38Zr_0.62O_12.31 phase increases with increasing concentration of Bi₂O₃. The AC conductivity plots exhibit phase transition at 570 °C and 460 °C for x = 10 and x = 15 samples, respectively. The maximum conductivity is observed (1.60 mS/cm) in x = 15 sample. These results are correlated and supported with microstructural and thermal analysis.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

PEO electrolytes containing dioctyl phthalate (DOP) for dye-sensitized nanocrystalline TiO2 solar cells

In this paper, we aim to prepare polymer electrolytes consisting of NaI and I₂ dissolved in poly(ethylene oxide) (PEO) and dioctyl phthalate (DOP) as an additive and apply the electrolytes to dye-sensitized solar cells (DSSC). Upon the incorporation of salt, the phthalic-stretching C=O bands of DOP in Fourier transform infrared spectra shifted to a lower wave number (Δf = 93 cm⁻¹), confirming the unusual strong complex formation between sodium ions and phthalic oxygen. Coordinative interactions and structural changes of PEO/NaI/I₂/DOP electrolytes have also been characterized by wide angle X-ray scattering, presenting an almost amorphous structure of the polymer electrolytes. The ionic conductivity of the polymer electrolytes reached ∼10^–4 S/cm at room temperature at the mole ratio of [EO]:[Na]:[DOP] = 10:1:0.5, as determined by the four-probe method. DSSC using the polymer electrolytes and conductive indium tin oxide glasses exhibited 2.9% of overall energy conversion efficiency (=P _max/P _in × 100) at one sun condition (100 mW/cm²). The good interfacial contact between the electrolytes and the dye-attached nanocrystalline TiO₂ layers were verified by field-emission scanning electron microscopy.     

Elastic properties of TeO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Ag<Subscript>2</Subscript>O glasses

A series of glasses [(TeO₂) _x (B₂O₃)_1−x ]_1−y [Ag₂O] _y with x = 70 and y = 10, 15, 20, 25 and 30 mol% were synthesised by rapid quenching. Longitudinal and shear ultrasonic velocity were measured at room temperature and at 5 MHz frequency. Elastic properties, Poisson's ratio, microhardness, softening temperature and Debye temperature have been calculated from the measured density and ultrasonic velocity at room temperature. The experimental results indicate that the elastic constants depend upon the composition of the glasses and the role of the Ag₂O inside the glass network is discussed. Estimated parameters based on Makishima–Mackenzie theory and bond compression model were calculated in order to analyse the experimental elastic moduli. Comparison between the experimental elastic moduli data obtained in the study and the calculated theoretically by the mentioned above models has been discussed.     

Ionic conductivity and structural properties of MnO-doped Bi4V2O11 system

Bi₄V₂O₁₁ exists in three phases viz. α, β, and γ. High temperature γ-phase can be stabilized to room temperature owing to its higher conductivity by the partial substitution of metallic cations for vanadium in Bi₄V₂O₁₁. Phase transitions from α → β and β → γ are composition and temperature-dependent. Mn²⁺-doped compounds Bi₄V_2−x Mn _x O_{11− δ} (0 ≤ x ≤ 0.4) have been synthesized by solid state reaction technique and investigated by X-ray diffraction and ionic conductivity measurement. High ionic conducting γ-phase is stabilized for x ≥ 0.2. The ionic conductivity of the series of Bi₄V_2−x Mn _x O_{11− δ} samples has been measured by using ac impedance spectroscopy technique. The conductivity data do show departure from its simple Arrhenius behavior for all of the compositions. The highest conductivity observed for x = 0.2 sample can be attributed to lower activation energy.     

Statistical theory of forming structural vacancies in palladium hydride

Based on molecular-kinetic representations, the theory of forming structural vacancies and vacant-ordered superstructure of Cu₃Au type in palladium hydride is developed. Free energies of PdH and Pd₃VH₄ phases are calculated. The constitution diagram is constructed that determines ranges of temperature and concentration in which phases with A1 and L1₂ structures are formed and regions of two A1 + L1₂ phases are realized. Results of theoretical calculations are in agreement with the available experimental data.     

Phase transformations and thermal stability of the structure of Ti<Subscript>3</Subscript>Al intermetallic compound at deuteration and plastic deformation

The structural transformations in Ti₃Al intermetallic compound at deuteration with concentrations x = 1.2 and 1.7, heating at 100–400°C, and shear deformation under pressure have been studied. It is established that at a given deuterium concentration deuterides with fcc and orthorhombic lattices are formed; under severe shear deformation, nanocrystalline and amorphous (or close to amorphous) deuterides arise. The reasons for the structure amorphization at deuteration and subsequent plastic deformation are discussed.     

Structural and dehydriding properties of Ca(BH<Subscript>4</Subscript>)<Subscript>2</Subscript>

We have investigated the structural and dehydriding properties of Ca(BH₄)₂. It was found that Ca(BH₄)₂ undergoes a structural phase transformation from an orthorhombic low-temperature (LT) modification into a tetragonal high-temperature (HT) modification between 433 K and 523 K. The amount of hydrogen desorbed from Ca(BH₄)₂ during the pressure–composition (p–c) isotherm measurement was 5.9 mass%. This hydrogen desorption is caused by the partial dehydrogenation of Ca(BH₄)₂ accompanied by the formation of CaH₂ and orthorhombic intermediate phases.     

Plastic-strain localization in barium fluoride single crystals at elevated temperatures

The strain distribution is studied in BaF₂ crystals subjected to compression tests along [110] and [112] at a constant strain rate in the temperature range T = (0.22–0.77)T _m. At T > 0.5T _m, the plastic strain in deformed samples is found to be strongly localized in narrow bands, where the shear strain reaches several hundred percent. The degree of localization increases with temperature. Localized-shear microbands are shown to be oriented along {001}〈110〉 slip systems. The phenomenon of serrated yielding is detected, and stress jumps (serrations) are established to correlate with the formation of shear zones.     

Structural and magnetic phases of Bi<Subscript>1−x</Subscript>A<Subscript>x</Subscript>FeO<Subscript>3−</Subscript><Subscript>δ</Subscript> (A = Sr,Pb) perovskites

The Bi_1−xA_xFeO_{3− δ} (A = Sr, Pb) systems have been studied using the X-ray, neutron powder diffraction and magnetization measurements in a magnetic field up to 14 T. It was found that around x ∼ 0.06 the crystal symmetry changes from a rhombohedral (space group R3c) to pseudo-tetragonal. In the composition range 0.07 ≤ x ≤ 0.14 the phases with different symmetry of the unit cell coexist independent of synthesis conditions. The neutron powder diffraction shows that the iron ions have average oxidation state close to 3+. The magnetic structure for Bi_0.5Sr_0.5FeO_{3− δ} is found to be G-type antiferromagnetic with magnetic moment of about 3.8 μ_B/Fe³⁺. The weak ferromagnetic state due to magnetoelectric interactions was revealed in the lightly doped rhombohedrally distorted compositions. No evidence for a spontaneous magnetization was observed for the pseudo-tetragonal phases. These compositions show irreversible nonlinear magnetization vs. field behavior apparently due to small local deviations from the collinearity of the magnetic moments.     

An EIS study of La2 − x Sr x NiO4 + δ SOFC cathodes

La_2 − x Sr _x NiO_{4 +  δ} materials were investigated as cathodes for the electrochemical reduction of oxygen on a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte using cone-shaped electrodes together with electrochemical impedance spectroscopy. The area-specific resistance (ASR) of the La_2 − x Sr _x NiO_{4 +  δ} nickelates towards the reduction of oxygen is equal to the ASR of perovskites; however, it is not as low as for the best Fe–Co-based perovskites. The lowest ASR is found for the compound La_1.75Sr_0.25NiO_{4 +  δ} with an ASR of 23.8 Ωcm² measured on a cone-shaped electrode in air at 600 °C. It is suggested that difference in oxide ionic conductivity of the nickelates is the main cause for the different activity of the nickelates towards the electrochemical reduction of oxygen.     

Spectra of Stimulated Electromagnetic Emission of the Ionosphere Upon Sweeping of the Pump Wave Frequency Near Gyroharmonics. I. Experimental Results

We present the results of experimental studies of the spectra of the stimulated electromagnetic emission excited in the ionosphere by powerful radio waves during the pump wave frequency sweeping near the forth (n = 4) and fifth (n = 5) harmonics of the electron cyclotron frequency nf _ce. The frequency sweep was carried out for long (continuous) pumping in vertical and inclined directions (at 14° and 18° south of the zenith), as well as for the pulse diagnostic wave both with and without additional pumping far from the gyroharmonics. The dependences of the spectral features of the stimulated electromagnetic emission on the ratio between the pump-wave frequency f ₀ (or on the diagnostic-wave frequency f_DW) and nf _ce were analyzed. It is found that near the multiple gyroresonance, different spectral features of the stimulated emission are quenched at the same frequency for different pump-wave frequencies. For a sufficiently large inclination of the pump wave beam from the vertical direction, the intensity of the stimulated electromagnetic emission is notably decreased for f ₀ ≲ nf _ce as compared with f ₀ > nf _ce. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 461–476, June 2008.     

Mechanism of the formation of a diamond nanocomposite during transformations of C60 fullerite at high pressure

The results of an investigation of the transformation of C₆₀ fullerite to diamond under pressure through intermediate three-dimensionally polymerized and amorphous phases are reported. It is found that treatment of fullerite C₆₀ at pressures 12–14 GPa and temperatures ∼1400°C produces a nanocrystalline graphite-diamond composite with a concentration of the diamond component exceeding 50%. At lower temperatures (700–1200°C) nanocomposites consisting of diamondlike (sp ³) and graphitic (sp ²) amorphous phases are formed. The nanocomposites obtained have extremely high mechanical characteristics: hardness comparable to that of best diamond single crystals and fracture resistance two times greater than that of diamond. Mechanisms leading to the transformation of C₆₀ fullerite into diamond-based nanocomposites and the reasons for the high mechanical characteristics of these nanocomposites are discussed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 822–827 (10 June 1999)     

Acidichromism and Ionochromism of Luteolin and Apigenin,the Main Components of the Naturally Occurring Yellow Weld: A Spectrophotometric and Fluorimetric Study

Luteolin and apigenin, extracted from Reseda luteola L., were spectrophotometrically and fluorimetrically studied. The spectra were investigated as a function of pH in methanol/water solutions (1/2, v/v) in the 2–12 pH range. The absorption spectra markedly shifted to the red by increasing the pH. Three acid–base dissociation steps were detected for luteolin (pK _a = 6.9; 8.6; 10.3) and two for apigenin (pK _a = 6.6; 9.3). Fluorescence emission was very weak or undetectable (Φ _F < 10⁻⁴) in acidic solution, but increased in intensity with increasing the pH. Both molecules exhibited a great propensity towards complex formation with metal ions, with association constants on the order of 10⁵–10⁷ for the first complexation step; in the presence of excess Al³⁺ ions, multiple equilibria were detected. A marked fluorescence enhancement was observed upon complexation with Al³⁺ ions (Φ _F ∼ 1 for luteolin and ∼10⁻² for apigenin).     

The NASICON solid solution Li1−x La x /3Zr2(PO4)3: optimization of the sintering process and ionic conductivity measurements

The Li_1−x La _{x /3}Zr₂(PO₄)₃ NASICON-type compounds (0 ≤ x ≤ 1) have been synthesized in powder form by a sol-gel method and sintered for ionic conductivity measurements. In order to improve the compactness of the ceramic without decomposition of the compound, several sintering processes have been tested for one member of the solid solution (x = 0.6): the use of sintering aids (ZnO, B₂O₃, TiO₂ and LiNO₃), a ball-milling of the synthesized powder, a flash heating, high isostatic pressure, and spark plasma sintering. Finally, a satisfactory compactness of 85% is obtained compared to the referenced value (63%) obtained by uniaxial and isostatic pressing. The ionic conductivity study was performed by impedance spectroscopy. It shows that, despite the formation of vacancies, the substitution Li⁺→ 1/3 La³⁺ + 2/3 □ has unfortunately no influence on the conduction for 0 ≤ x ≤ 0.7 since the ionic conductivity remains identical to the LiZr₂(PO₄)₃ one. For higher x values, the ionic conductivity strongly decreases.     

Steady State and Time-Resolved Fluorescence Studies of a Hemagglutinin from Moringa oleifera

The saccharide binding and conformational characterization of a hemagglutinin, a low molecular weight protein from the seeds of Moringa oleifera was studied using steady state and time resolved fluorescence. The lectin binds sugars LacNAc (K _a = 1380 M⁻¹) and fructose (K _a = 975 M⁻¹), as determined by the fluorescence spectroscopy. It has a single tryptophan per monomer which is exposed on the surface and is in a strong electropositive environment as revealed by quenching with iodide. Quenching of the fluorescence by acrylamide involved both static (K _s = 0.216 M⁻¹) and collisional (K _sv = 8.19 M⁻¹) components. The native protein showed two different lifetimes, τ ₁ (1.6 ns) and τ ₂ (4.36 ns) which decrease and get converted into a single one, (2.21 ns) after quenching with 0.15 M acrylamide. The bimolecular quenching constant, k _q was 7.55 × 10¹¹ M⁻¹ s⁻¹. ANS binding studies showed that the native protein has exposed hydrophobic patches which get further exposed at extreme acidic or alkaline pH. However, they get buried in the interior of the protein in presence of 1 M GdnHCl or urea.     

Cuspons and Smooth Solitons of the Degasperis–Procesi Equation Under Inhomogeneous Boundary Condition

This paper is contributed to explore all possible single peakon solutions for the Degasperis–Procesi (DP) equation m _t  + m _x u + 3mu _x  = 0, m = u − u _xx . Our procedure shows that the DP equation either has cusp soliton and smooth soliton solutions only under the inhomogeneous boundary condition lim_|x|→ ∞ u =A ≠0, or possesses the regular peakon solutions ce ^{− |x − ct|} ∈ H ¹ (c is the wave speed) only when lim_|x|→ ∞ u = 0 (see Theorem 4.1). In particular, we first time obtain the stationary cuspon solution of the DP equation. Moreover we present new cusp solitons (in the space of ) and smooth soliton solutions in an explicit form. Asymptotic analysis and numerical simulations are provided for smooth solitons and cusp solitons of the DP equation.      

Nanocrystalline platinum layer deposited on NiTiCu shape memory strip

The Ni₂₅Ti₅₀Cu₂₅ shape memory strip was covered by thin nanocrystalline platinum layer. Structure of the layer was studied by means of X-ray diffraction and transmission electron microscopy. Transformation temperatures were determined using differential scanning calorymetry (DSC). The studies show that the layer reveals nanocrystalline structure with average crystalline size of 44 nm. Lattice distortion was relatively low –0.19%. Almost 25% of total grains are oriented along 〈111〉 direction. It was stated that the nanocrystalline platinum layer does not limit martensitic transformation in the covered strip, which reveals one step reversible martensitic transformation from the parent B2 phase to the orthorhombic martensite B19 phase. Also no influence of the layers on the shape recovery was noticed.