Effect of Li2O on structure and optical properties of lithium bismosilicate glasses

Bismuth–silicate glasses containing lithium oxide having composition xLi₂O·(85 − x)Bi₂O₃·15SiO₂ (5 ≤ x ≤ 45 mol%) were prepared by melt quench technique. Density, molar volume and glass transition temperature for all the glass samples were measured. IR spectroscopy was used for structural studies of these glasses in the range from 400 to 1400 cm⁻¹. The increase of Li₂O content in glass matrix results in the decrease of the Si–O–Si bond angle and increase in the covalence nature of Bi–O bond. IR spectra suggest the presence of distorted [BiO₆] octahedral units and the degree of distortion increases with the addition of Li₂O in these glasses. The optical transmission spectra in the wavelength range from 200 to 3300 nm were recorded and optical band gap (E_g) was calculated. The values of E_g lie in between 2.81 and 2.98 eV. The values of average electronic oxide polarizability as well as optical basicity in these glasses were found to be dependent directly on Bi₂O₃/Li₂O ratio.     

Synthesis and photocatalytic properties of Sn-doped TiO2 nanotube arrays

TiO₂ nanotube arrays doped by Sn up to 12 at% have been prepared using template-based liquid phase deposition method. Their morphologies, structures and optical properties have been investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–vis absorption spectroscopy and photoluminescence spectroscopy. The photocatalytic properties of the samples were evaluated with the degradation of methylene blue under UV irradiation. The result shows that doping an appropriate amount of Sn can effectively improve the photocatalytic activity of TiO₂ nanotube arrays, and the optimum dopant amount is found to be 5.6 at% in our experiments.     

The Yb–Zn–In system at 400 °C: Partial isothermal section with 0–33.3 at.% Yb

The phase relations in the ternary system Yb–Zn–In have been established for the partial isothermal section in the 0–33.3 at.% ytterbium concentration range at 400 °C, by researching of more than forty alloys. X-ray powder diffraction (XRPD), optical microscopy (OM) and scanning electron microscopy (SEM), complemented with energy dispersive X-ray spectroscopy (EDS), were used to study the microstructures, identify the phases and characterize their crystal structures and compositions. The phase equilibria of this Yb–Zn–In partial section at 400 °C are characterized by the presence of three extended homogeneity ranges, indium solubility in Yb₁₃Zn₅₈ and YbZn₂ and of zinc solubility in YbIn₂, and the existence of one ternary intermetallic compound, YbZn_1−xIn_1+x, x = 0.3. This new compound crystallizes in the UHg₂ structure type (space group P6/mmm), with a = 4.7933(5) Å, c = 3.6954(5) Å. The studied partial isothermal section has eight ternary phase fields at 400 °C.     

Composition-controlled synthesis, structure and magnetic properties of ternary FexCoyNi100−x−y alloys attached on carbon nanotubes

Fe_xCo_yNi_100−x−y alloy nanoparticles with controllable compositions attached on the surface of carbon nanotubes (CNTs) were synthesized using an easy two-step route including adsorption and reduction processes. The nanocomposites have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). The effect of the alloy composition on microstructure and magnetic properties of ternary FeCoNi alloys attached on carbon nanotubes have been studied. During the nominal composition range (x = 21, 24, 33, 37, 46 and y = 60, 46, 48, 48, 35), Fe_xCo_yNi_100−x−y alloy nanoparticles attached on CNTs are quasi-spherical, fcc–bcc dual phase, and the coercivity (H_c) and saturation magnetization (M_s) vary with the alloy composition. The H_c of Fe_xCo_yNi_100−x−y alloy nanoparticles attached on CNTs decreases and M_s increases with increasing Fe content. These demonstrate that the two-step route is promising for fabricating alloy nanoparticles attached on CNTs for magnetic storage and ultra high-density magnetic recording applications.     

Structures, electrical and thermal expansion properties of Sr-doped La2Mo2O9 oxide-ion conductors

The oxide-ion conductors (La_1−xSr_x)₂Mo₂O_9−δ (x = 0.01–0.08) were prepared by means of a conventional solid-state reaction. The effects of Sr doping for La site on the structures, electrical and thermal expansion properties of the oxide-ion conductor La₂Mo₂O₉ were investigated using X-ray diffraction, direct current four-probe method, thermal dilatometer and scanning electron microscopy, respectively. The results show that the lattice constants were first decreased, then increased, and decreased again with the increase of Sr doping content. The solid solubility of Sr in (La_1−xSr_x)₂Mo₂O_9−δ is x = 0.07. The sinterability of samples is markedly improved with the increase of Sr doping content. The sintered density of sample x > 0.07 is higher than 96% of its theoretical density. When x > 0.02, doping Sr in La₂Mo₂O₉ can inhibit the excessive growth of grains, thus increases the sintered density of samples. The structural transition temperature shifts to the low side with the increase of Sr doping content, and the phase transition is completely suppressed when the doping content reaches 0.07. The conductivity of sample increases with the increase of Sr doping content. The conductivity of sample x = 0.07 reaches a maximum of 0.078 S/cm and 0.101 S/cm at 800 °C and 850 °C, respectively. In this study, it was demonstrated that doping 7 mol% Sr for La site not only can completely suppress the structural phase transition in La₂Mo₂O₉, but also can effectively enhance electrical conductivity of samples at higher temperature.     

Thermoelectric properties of Sn1−x−yTiySbxO2 ceramics

Thermoelectric properties of Sn_1−x−yTi_y Sb_xO₂ ceramics were investigated in detail. The addition of Sb into SnO₂ matrix increased the electric conductivity, σ. The increase in the σ value should be caused by the increase in the carrier concentration. The Seebeck coefficients of all the samples were negative, which means that these samples have n-type conduction. The samples of this study have porous structure. The maximum Z value of all the samples measured in this study was 2.4 × 10⁻⁵ K⁻¹.     

Magnetic study of Ti-substituted NiFe2O4 ferrite

The Ni_1+xTi_xFe_2−2xO₄ (0 ≤ x ≤ 0.1) ferrite systems prepared by a semi-chemical route, have been studied by electron paramagnetic resonance (EPR) at X-band, Mössbauer spectroscopy and magnetization measurements at various temperatures. EPR spectra of these samples comprise generally a broad and asymmetric EPR signal. The variation of g_eff and peak-to-peak line width ΔH_pp, with Ti concentration and temperature are attributed to the variation of dipole–dipole interaction and the superexchange interaction. Mössbauer spectra comprise two sets of sextet attributed to Fe³⁺ at two distinct sites-A and -B. Ti⁴⁺ ions are concluded to occupy the octahedral B-sites. Magnetic moment is found to decrease with the increase of Ti⁴⁺ concentration. The effective magnetic field H_eff at the A-sites also follows a similar trend. The reason is attributed to the canted structure of spins in the Ti-doped samples. An anomalous behavior at x = 0.015 is observed in the properties studied here and some sort of phase change is believed to occur at 473 K in these ferrites.     

Microwave synthesis and characterization of Zn-doped nickel ferrite nanoparticles

Microwave assisted combustion method was used to synthesize nanocrystalline Zn_xNi_1−xFe₂O₄ from a stoichiometric mixture of corresponding metal nitrates and urea powders. The structural, chemical and magnetic properties of Ni–Zn ferrite was determined by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM) and DC conductivity measurements. Results showed that the material was spinel structure with a high purity with an estimated crystallite size of 20 nm by X-ray line profile fitting. TEM analysis showed necked near-spherical particles with an average size of 20 nm, reflecting highly crystalline nature of these nanoparticles. Magnetic properties showed anomalities as the Zn doping level increased. This has been explained and attributed to the relative positions of Ni, Zn, and Fe ions in the crystal lattice.     

Wear-resistant Ti–B–N nanocomposite coatings synthesized by reactive cathodic arc evaporation

Wear-resistant Ti–B–N coatings have been synthesized by reactive arc evaporation of Ti–TiB₂ compound cathodes in a commercial Oerlikon Balzers Rapid Coating System. Owing to the strong non-equilibrium conditions of the deposition method, a TiN–TiB_x phase mixture is observed at low N₂ partial pressures, as determined by elastic recoil detection analysis, X-ray diffraction, X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction. The indicated formation of a metastable solid solution of B in face-centered cubic TiN gives rise to a maximum in hardness (>40 GPa) and wear resistance on the expense of increased compressive stresses. A further saturation of the nitrogen content results in the formation of a TiN–BN nanocomposite, where the BN phase fraction was tailored by the target composition (Ti/B ratio of 5/3 and 5/1). However, the amorphous nature of the BN phase does not support self-lubricious properties, showing friction coefficients of 0.7 ± 0.1 against alumina. The effect of an increased bias voltage on structure and morphology was investigated from −20 to −140 V and the thermal stability assessed in Ar and air by simultaneous thermal analysis up to 1400 °C.     

Preparation of W–15 wt%Ti prealloyed powders

W–15 wt%Ti prealloyed powders were prepared by high-energy milling W and TiH₂ powders, and the prealloyed powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The size of W and TiH₂ grains was estimated by Williamson–Hall formula from width of XRD peaks. The results show that the grain size decreases with increasing milling time, while the lattice parameter increases. After milling for 40 h, nanocrystalline β-W_xTi_1−x solid solution with the form of thin laminar exists in the W–TiH₂ prealloyed powders.     

Synthesis of VN nanopowders by thermal nitridation of the precursor and their characterization

Vanadium nitride (VN) nanopowders can be synthesized by thermal nitridation of the precursor of ammonium vanadate (NH₄VO₃) and nanometer carbon black. The products were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the single phase VN powders can be synthesized at 1100 °C for 1 h, and the powders show good dispersion and are mainly composed of uniformly sized spherical particles with a mean diameter of 50 nm. The surface of the specimen mainly consists of V, N, O and C four species elements, the peak core at 397.24 eV corresponds to N 1s of VN. The O 1s peaks with the binding energies of 530.40 eV and 532.15 eV are ascribed to vanadium pentoxide (V⁵⁺) and H₂O (OH⁻), and the contents are very little. The C 1s profile is a single symmetric peak, which mainly comes from the polluted carbon used for the correction of the XPS measurement.     

Structural, electrical and magnetic properties of Cu1−xZnxFe2O4 ferrites (0 ≤ x ≤ 1)

Copper–zinc ferrites bearing chemical formula Cu_1−xZn_xFe₂O₄ for x ranging from 0.0 to 1.0 with the step increment of 0.2 were prepared by the standard solid-state technique. The variation of Zn substitution has a significant effect on the structural, electrical and magnetic properties. Lattice parameters ‘a’ increased from 8.370 to 8.520 Å. Dielectric constant decreased up to 311 with the increase in frequency from 80 Hz to 1 MHz at room temperature. All the samples follow the Maxwell–Wagner's interfacial polarization. Saturation magnetization, magnetic moment and Yafet–Kittel angles were also determined. The possible reasons responsible for the change in density related, electrical and magnetic properties with the increase in Zn concentration are undertaken.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

Formation and properties of the Zr75−xAlxNi10Cu10Ti5 bulk metallic glasses

Zr-based bulk metallic glasses (BMGs) exhibit interesting mechanical properties since they combine high fracture stress, elastic strain (up to 2%), significant fracture toughness and good corrosion resistance. Quaternary systems with general composition Zr–Ni–Cu–Ti show wide composition ranges in which BMG can be obtained. The addition of the another element to the quaternary alloys often increases the glass forming ability (GFA). The aim of this work was to study the influence of aluminium content on the GFA and on the mechanical properties of the Zr–Ni–Cu–Ti alloys. Multicomponent Zr_75−xAl_xNi₁₀Cu₁₀Ti₅ (x = 15, 20 at%) alloys were produced by melt spinning method obtaining ribbons, and by casting technique into a copper mould, manufacturing rod shape samples with maximum diameter of 2 mm. Supercooled liquid region depends on chemical composition and exceeds 45 °C. Vickers microhardness of studied alloys is comparable to the highest ones for other Zr-based BMG.     

X-ray diffraction study of Ba0.985Na0.015Ti0.985Nb0.015O3, Ba0.6Na0.4Ti0.6Nb0.4O3 and Ba0.3Na0.7Ti0.3Nb0.7O3 compositions

The Ba_0.985Na_0.015Ti_0.985Nb_0.015O₃, Ba_0.6Na_0.4Ti_0.6Nb_0.4O₃ and Ba_0.3Na_0.7Ti_0.3Nb_0.7O₃ compositions of the (1 − x) BaTiO₃–xNaNbO₃ (BTNNx) system have been studied by X-ray diffraction and by measurements of dielectric properties. The specimens with composition BTNN (x = 0.015, 0.40 and 0.70) have been refined by the JANA program from X-ray powder diffraction data. Ceramic samples with composition (1 − x) BaTiO₃ + xNaNbO₃ (where x = 0.015, 0.40 and 0.70) were prepared by calcinations from appropriate mixture of BaCO₃, TiO₂, Na₂CO₃ and Nb₂O₅. The calcined powder was sintered at temperature range 1200–1400 °C. As the composition x increased from 0.015 (and 0.70), the ferroelectric ceramics (x = 0.015, FE) with tetragonal phase changed to the ferroelectric relaxors (RFE, x = 0.40). RFE ceramics showed a peculiar diffuse phase transition and dielectric relaxation at the low temperature (down to 180 K) due to a frustration between RFE and FE state. These ceramics present the classical ferroelectric character when 0 ≤ x < 0.075 and 0.55 < x ≤ 1 and relaxor character when 0.075 ≤ x ≤ 0.55.     

Dielectric and magnetic properties of 0.7Bi(Fe1−xCrx)O3–0.1BaTiO3–0.2PbTiO3 solid solutions

0.7Bi(Fe_1−xCr_x)O₃–0.1BaTiO₃–0.2PbTiO₃ (x = 0, 0.1, 0.2, 0.3) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results revealed that the samples with x = 0–0.3 showed pure perovskite structure. Frequency and temperature dependences of dielectric constants and dielectric loss of the samples were investigated. Both dielectric constant and the loss tangent increased at given frequencies (100 Hz–1 MHz), while the Curie temperature of the solid solutions decreased with increasing Cr content. Room temperature magnetic hysteresis loops indicated that an appropriate amount of Cr could improve magnetization of the solid solutions.     

Gas phase synthesis of SnOx nanoparticles and characterization

Tin oxide nanoparticles with an average size ranging from 4 to 80 nm were synthesized by oxidation of tin vapor in a low vacuum (10–40 mbar) reactor containing an Ar/O₂ gas mixture. The effect of oxygen and argon partial pressure on the phase formation, size characteristics and morphology of the particles was studied by transmission electron microscopy (TEM) and X-ray diffraction (XRD) method. Electron spectroscopy chemical analysis (ESCA) was used to study the state of the particle surfaces. It was shown that with increasing the oxygen partial pressure, coarser SnO_x particles were synthesized. The ESCA shift for the tin 3d_5/2 line was 2 eV and the separation between this line and the oxygen 1s line was 44 eV. The oxygen 1s line was narrow and symmetric without the OH tail, indicating clean surface. The O/Sn ratios were estimated by using the areas of the tin and oxygen lines, and it was found that the oxidized tin vapor consisted of both SnO and SnO₂. At the oxygen concentration of 50 vol% and the total pressure of 10 mbar, the surface composition was estimated to be SnO_1.2. The particles were transformed to tetragonal SnO₂ after heat treatment at 350 °C for 24 h in air.     

Preparation of Ti–Al–Si alloys by reactive sintering

The isothermal section of the Dy–Co–Ti system at 500 °C has been investigated in the whole composition range by means of X-ray diffraction, thermal analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. The only ternary phase DyTi_xCo_12−x is of ThMn₁₂-type structure, space group I4/mmm, and shows a small homogeneity range of 1 ≤ x ≤ 1.6. The lattice parameters for DyTi_xCo_12−x with 1 ≤ x ≤ 1.56 are a = 0.8336(4)–0.8402(1) nm and c = 0.4691(3)–0.4727(1) nm. Along a constant Dy concentration, the solid solubilities of Ti in the compounds Dy₂Co₁₇, DyCo₃, DyCo₂ and Dy₃Co are about 2.0, 2.0, 3.0 and 4.0 at.%, respectively. The TiCo phase has a homogeneity range of 50–54 at.% Co at 500 °C and dissolves up to 2.0 at.% Dy.     

Synthesis and measurement of structural and magnetic properties of K-doped LaCoO<Subscript>3</Subscript> perovskite materials

Polycrystalline La_1−x K _x CoO₃ (0 ≤ x ≤ 0.2) rare earth cobaltates have been synthesized by a solution combustion method using glycine as a fuel. The synthesized ceramic materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and magnetic measurements and studied for physical properties, such as photocatalytic activity. FTIR measurements in conjunction with XRD showed that phases beyond 10% K doping are accompanied by small amounts of impurities. Chemical titrations show the presence of Co⁴⁺ and account for the Co³⁺-Co⁴⁺ mixed-valency of the system. The parent LaCoO₃ shows spin-glass transition at low temperatures, whereas doped samples show transition from spin-glass behavior to paramagnetic ordering on progressive doping of K. “Mixed-conductor” nature of these ceramics positions them as viable candidates for solid oxide fuel cell (SOFC) applications.     

Influence of the borohydride concentration on the composition of the amorphous Fe–B alloy produced by chemical reduction of synthetic, nano-sized iron-oxide particles: Part I: Hematite

Amorphous Fe–B alloys can be prepared at room temperature by reduction with borohydride of iron-oxide particles in suspension. By varying the borohydride concentration, amorphous Fe–B alloys with boron contents between 2 and 13 at.% have been produced by reduction of synthetic (nano-sized particles) and natural (micro-sized) hematite (α-Fe₂O₃) using sodium borohydride (NaBH₄). The results presented in this paper were obtained from a systematic study of the effect of borohydride concentration on the resulting reaction products using a variety of experimental techniques, such as X-ray diffraction, wet chemical analyses, thermal analyses, scanning electron microscopy, transmission Mössbauer spectroscopy (TMS) and integral low-energy electron Mössbauer spectroscopy (ILEEMS). Three distinct NaBH₄ concentrations have been applied. Beside unreacted hematite, amorphous Fe_1−xB_x alloys have been identified from the TMS spectra recorded at various temperatures between 15 K and room temperature. The amount of Fe_1−xB_x increases strongly with increasing NaBH₄ concentration, and for a given concentration with increasing specific surface area (SSA). Thermal analyses have suggested that for any given reduction condition, the boron content x in the formed amorphous alloy has a bimodal distribution. This is found to be consistent with the finding that the contribution of the Fe_1−xB_x phase to the total Mössbauer spectra consists of a superposition of a broad sextet and doublet. ILEEMS has further revealed that especially the surface layers of the hematite grains are affected by the reduction processes.