The influences of firing temperatures and excess PbO on the crystal structure and microstructure of (Pb<Subscript>0.25</Subscript> Sr<Subscript>0.75</Subscript>)TiO<Subscript>3</Subscript> ceramics

Polycrystalline samples of (Pb_0.25Sr_0.75)TiO₃ (PST75) were prepared by the solid-state reaction method. The effects of firing temperatures and excess PbO on PST75 ceramics were investigated. The PST75 was calcined between 600 and 1000 °C for 3 h and the sintering temperature ranged between 1050 and 1250 °C for 2 h. The optimized calcination and sintering conditions were identified as 950 and 1250 °C, respectively. The lattice parameter c increased, while the lattice parameter a decreased with increased firing temperatures. The average particle size and average grain size increased with increased firing temperatures. After the addition of PbO—excess 0, 1, 3, 5, and 10 wt%—in the PST75 samples, the lattice parameter a decreased. The average particle size and the average grain size increased with the increase of PbO. The porous microstructure slightly decreased with an increasing amount of PbO—up to 3 wt%—then slightly increased with the higher excess PbO. The density was improved by adding 3 wt% of excess PbO. A low dielectric loss was observed from the 3 wt% excess PbO sample.     

Microstructure and properties of 3D needle-punched carbon/silicon carbide brake materials

The carbon/silicon carbide brake materials were prepared by chemical vapor infiltration (CVI) combined with liquid melt infiltration (LMI). The carbon fiber preform was fabricated with the three dimension needling method. The microstructure, mechanical, thermophysical, and frictional properties of C/SiC composites were investigated. The results indicated that the composites were composed of 65 wt%C, 27 wt%SiC, and 8 wt%Si. The density and porosity were 2.1 g cm⁻³ and 4.4%, respectively. The C/SiC brake materials exhibited excellent toughness. The average dynamic friction coefficient and static friction coefficient of the materials were about 0.34 and 0.41, respectively. The friction coefficient was stable. The fade ratio of the friction coefficient under moist conditions was about 2.9%. The linear wear rate was less than 1.9 μm side⁻¹ cycle⁻¹. These results show that C/SiC composites have excellent properties for use as brake materials for aircraft.     

Arc-evaporated CrN, CrN and CrCN coatings

The results of investigations of some tribological properties of chromium nitride, carbonitride and carbide films, prepared by cathodic arc-evaporation method (CAE) are presented in this article. The chemical composition of films was determined by the WDXs and EDXs. The different carbon content was obtained by using nitrogen and acetylene mixtures of various concentrations as the deposition atmosphere. The carbon content was ranging from 0 to 53 at.%. The adhesion of CrCN films was estimated from the analysis of scratch-test results comprising tangential (friction) force, acoustic emission and morphology of scratch surface. The films showed very good adhesion to steel substrates, expressed by L_c (critical load) value, as high as 90 N for carbon free films. The L_c decreased slightly as the carbon content increased. The hardness of films was investigated as a function of carbon content and was estimated by Jönsson-Hogmark method. The L_c value and hardness seem to be correlated in the same way with carbon content. The highest hardness (30 GPa) was obtained for CrN films, while carbon rich films (CrC) showed hardness at the level of 20 GPa. The tribological tests were performed in the ball-on-disk geometry in room air under the load of 1 N and 10 N. The wear rate of investigated films increased with carbon content above 20 at.%. The maximum value of the friction coefficient was 0.55, the same as for CrN films. It decreased to 0.33 as the carbon content increased.     

Linear and nonlinear optical properties and luminescence of Dy+3-doped aluminoborate glasses: Judd–Ofelt investigation

The nominal glasses composition ((40-x) % H₃BO₃—30% CaO—30% Al₂O₃—x Dy₂O₃), where x?=?1, 2, 3, 4, 5 and 6) were prepared using the melt quenching technique. The absorption spectra reveal the common normal 13 transition peaks of the Dy₂O₃-doped glasses. The linear and nonlinear optical properties were calculated. The Photoluminescence spectra and the decay lifetime were examined. The Judd–Ofelt parameters trend was Ω₄?>?Ω₂?>?Ω₆. The oscillator strength of the experimental, and calculated electronic dipole absorption transition were estimated. The radiative life-time, the radiative branching ratio, the emission and absorption transition cross section were also calculated. The gain coefficient of the transitions was predicted. All the calculated parameters were compared with the previous work. The results reveal that the current glasses composition is a good candidate as a lasing host material and the glasses are highly efficient composition when using in the optical communication fibers.

     

Synthesis,growth and characterization of π conjugated organic nonlinear optical chalcone derivative

A new potentially useful nonlinear optical organic material, 1-(5-chlorothiophen-2-yl)-3-(2,3-dimethoxyphenyl)prop-2-en-1-one, has been synthesized and grown as a high-quality single crystal by the slow evaporation technique. The grown crystals were characterized by FT-IR, NMR, thermal analysis, and UV–visible spectroscopy. The material is thermally stabile up to 111 °C. The mechanical property of the grown crystals was studied using Vickers microhardness tester and the load dependence hardness was observed. The third order nonlinear optical properties of the material such as real and imaginary part of χ⁽³⁾, nonlinear absorption coefficient and nonlinear refractive index were determined using nanosecond laser pulses at 532 nm wavelength by employing Z-scan technique. The nonlinear refractive index is found to be of the order of 10⁻¹¹ cm² W⁻¹. The magnitude of third order susceptibility is of the order of 10⁻¹³ esu. The observed increase in the third order nonlinearity in these molecules clearly indicates the electronic origin. The compounds exhibit good optical limiting at 532 nm. The best optical limiting behavior of this molecule is due to the substituted strong electron donor.     

Solar photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using TiO2/SiO2 aerogel composite photocatalysts

Silica aerogels and TiO₂/silica aerogel composite photocatalysts were synthesized by sol–gel technique at ambient pressure using orthosilioate and tetra-n-butyl titanate as precursors, respectively. The prepared composite photocatalysts were characterized by XRD, TEM, BET surface area, FT-IR and UV–vis absorption spectra. The results showed that the TiO₂/silica aerogel composite photocatalysts possess high surface area. The addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination. The TiO₂/silica aerogel composite sample calcined at 500 °C with an optimal silica aerogel content of 7 wt.% afforded the highest photocatalytic activity. The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) was investigated by using this novel TiO₂/silica aerogel composite photocatalyst under solar light irradiation. The effects of irradiation time, pH, catalyst concentration, temperature and initial DNBP concentration were examined as operational parameters. The optimal operational parameters were found as follows: pH as solution pH 4.82, 8 g L⁻¹ catalyst concentration, 20 °C, and 240 min irradiation time. The kinetics of DNBP degradation by TiO₂/silica aerogel composite fit well a pseudo-first-order kinetic model. The repeatability of photocatalytic activity was also tested. This study showed the feasible and potential use of TiO₂/silica aerogel composite photocatalysts in degradation of toxic organic contaminants.     

Structural, spectroscopic and dielectric investigations on Ba8Zn(Nb6−xSbx)O24 microwave ceramics

Ba₈Zn(Nb_6−xSb_x)O₂₄ (x = 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 and 2.4) ceramics were prepared through the conventional solid-state route. The materials were calcined at 1250 °C and sintered in the range 1400-1425 °C. The structure of the system was analyzed by X-ray diffraction, Fourier transform infrared and Raman spectroscopic methods. The theoretical and experimental densities were calculated. The microstructure of the sintered pellets was analyzed using scanning electron microscopy. The low frequency dielectric properties were studied in the frequency range 50 Hz-2 MHz. The dielectric constant (?_r), temperature coefficient of resonant frequency (τ_f) and the unloaded quality factor (Q_u) are measured in the microwave frequency region using cavity resonator method. The τ_f values of the samples reduced considerably with the increase in Sb concentration. The materials have intense emission lines in the visible region. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Synthesis and characterization of porous platelet-shaped α-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> with enhanced photocatalytic activity for 17α-ethynylestradiol

The porous platelet-shaped α-Bi₂O₃ photocatalyst was successfully synthesized by a novel hydrothermal–calcination method assisted with ethylenediamine and polyvinylpyrrolidone. The physical and chemical properties of α-Bi₂O₃ photocatalyst were characterized based on XRD, XPS, SEM, TEM, EDS, UV–Vis DRS, and PL techniques. The influence of preparation conditions on the formation of α-Bi₂O₃ photocatalyst was investigated, and the effect of catalyst dosage and pH value on the EE2 removal rate was also investigated. The synthesized porous platelet-shaped α-Bi₂O₃ photocatalyst exhibited excellent photocatalytic activity for 17α-ethynylestradiol (EE2), and 97.8% of EE2 was removed after 75 min of visible light irradiation using α-Bi₂O₃ as photocatalyst. The reaction rate constant over the porous platelet-shaped α-Bi₂O₃ photocatalyst was 11.6 and 11.4 times of that of traditional α-Bi₂O₃ and N-TiO₂, respectively. The possible photocatalytic mechanism has been discussed on the basis of the theoretical calculation and the experimental results. The porous platelet-shaped α-Bi₂O₃ was a stable and efficient photocatalyst, proving that it is a promising photocatalyst.     

Structural and dielectric spectroscopy studies of the M-type barium strontium hexaferrite alloys (Ba x Sr1? x Fe12O19)

The M-type barium hexaferrite Ba _x Sr_1−x Fe₁₂O₁₉ (where 0 < x < 1) alloys were prepared by a new ceramic procedure. The samples were studied using X-ray diffraction and Rietveld analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, infrared and M?ssbauer spectroscopy. The X-ray analysis indicates that the all the samples present a hexagonal structure. The IR spectra showed three main absorption bands in range of 400–600 cm⁻¹ corresponding to SFO100 and BFO100. The M?ssbauer spectra showed a superposition of five subspectra associated with the five sites of the iron ion, which in the ferric state. The SEM studies showed that the hexaferrites presented grains that varied in the range of 260–305 nm. The dielectric properties: dielectric constant (ε′) and dielectric loss (tg δ) were measured at room temperature in the frequency range from 100 Hz to 40 MHz. The samples present a nonlinear behavior for the dielectric constant at 100 Hz, 1 kHz and 1 MHz. The dielectric constant is not following the linear mixing rule for the samples. The structural, dielectric and magnetic properties of the composite barium hexaferrite phases were discussed in view of applications as a material for permanent magnets, high density magnetic recording and microwave devices.     

Structure and Properties of La0.6Sr0.4 – xBaxMnO3 (0 ≤ x ≤ 0.4) Magnetoresistive Ceramics

The effect of Ba content on the phase composition, lattice parameter, ⁵⁵Mn NMR spectrum, resistance, and magnetoresistance of La_0.6Sr_{0.4 – x} Ba _x MnO₃ perovskites was studied. The lattice parameter of the single-phase ceramic samples was found to increase with increasing x. The tolerance factor increases and the ionic field strength decreases asx increases from 0 to 0.4. The ⁵⁵Mn NMR results obtained at 77 K indicate a high-frequency electron exchange between Mn³⁺ and Mn⁴⁺ in the ferromagnetic phase. The peak-magnetoresistance temperature tends to decrease with increasing x. The magnetoresistance of the ceramics is correlated with the bond covalence. It is inferred that the ceramics contain inhomogeneities differing in nature and length scale (macroscopic, mesoscopic, and microscopic), which influence their magnetoresistance.     

Ab initio study of AlCu2M (M = Sc,Ti and Cr) ternary compounds under pressures

The structural, electronic and elastic properties of the AlCu₂M (M = Sc, Ti and Cr) compounds in the pressure range of 0–100 GPa was investigated based on density functional theory. The calculated lattice parameters of the AlCu₂M compounds at zero pressure and zero temperature are in very good agreement with the existing experimental data. The bulk modulus, shear modulus and Young’s modulus increases with the increase of pressure, which indicates that higher materials hardness may be obtained when increasing pressures. The bulk modulus and Young’s modulus of AlCu₂Cr is the greatest under pressure. The shear modulus of AlCu₂Ti is the highest above 30 GPa, while that of the AlCu₂Sc is the strongest below 30 GPa. The calculated B/G values at zero and higher pressure indicated that they are ductile materials. The electronic densities of states and bonding charge densities have been discussed in details, revealing these compounds exhibit half-metallic behavior. In addition, the pressure dependences of Debye temperatures of AlCu₂M compounds have also been calculated. The results indicate that Debye temperatures increase with increasing pressure.     

Densities and Excess,Apparent, and Partial Molar Volumes of Binary Mixtures of BMIMBF<Subscript>4</Subscript> + Ethanol as a Function of Temperature,Pressure, and Concentration

The densities of five BMIMBF₄ (1-butyl-3-methylimidazolium tetrafluoroborate) + ethanol binary mixtures with compositions of (0.0701, 0.3147, 0.5384, 0.7452, and 0.9152) mole fraction BMIMBF₄ and of pure BMIMBF₄ have been measured with a vibrating-tube densimeter. Measurements were performed at temperatures from 298 K to 398 K and at pressures up to 40 MPa. The total uncertainty of density, temperature, pressure, and concentration measurements were estimated to be less than 0.1 kg · m⁻³, 15 mK, 5 kPa, and 10⁻⁴, respectively. The uncertainties reported in this article are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The measured densities were used to study derived volumetric properties such as excess, apparent, and partial molar volumes. It is shown that the values of excess molar volume for BMIMBF₄ + ethanol mixtures are negative at all measured temperatures and pressures over the whole concentration range. The effect of water content on the measured values of density is discussed. The volumetric (excess, apparent, and partial molar volumes) and structural (direct and total correlation integrals, cluster size) properties of dilute BMIMBF₄ + ethanol mixtures were studied in terms of the Krichevskii parameter. The measured densities were used to develop a Tait-type equation of state.     

The structure and optical dispersion of the refractive index of tellurite glass

The structure and optical properties of a 80TeO₂-(20−x)Li₂O-xTiO₂ glass system where x = 0, 5, 10, and 15 mol% has been investigated using FTIR spectroscopy and Brewster angle measurements. The sample preparation, linear refractive index and density measurements, and infrared spectroscopic analysis are described. The refractive index and density of the studied tellurite glass samples increase when the amount of Ti in the glass is increased. The dispersion of the phase refractive index was analyzed using Wemple’s model. The dispersion energy E_d is significantly affected by the addition of Ti to TeO₂-based glass. The analysis of FTIR spectra indicate a Te coordination change that is in agreement with the increase of the Te coordination number determined from dispersion data using Wemple’s equation.     

Effect of poly(ethylene glycol) surfactant on carbon-doped MoO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript> nanocomposite materials and its photocatalytic activity

Carbon-doped MoO ₃ samples were prepared by impregnation method. The effect of addition of polyethylene glycol-400 (PEG-400) and carbon (0, 1, 2 and 3 wt. %) as substrates, were investigated systematically to get the desired phase of carbon-doped MoO ₃ material. The carbon used was prepared from the natural sources such as Acacia arabika plant wood. The resulting samples were calcined at 500°C. The effect of PEG-400 and carbon composite on the structure, particle size and morphology of MoO ₃ was investigated. The samples thus prepared gave better control of particle size and porosity. The prepared samples were characterized using XRD, SEM–EDS and FT–IR techniques. Photocatalytic activities of the samples were studied with degradation of methylene blue. The 3 wt.% carbon-doped MoO ₃ modified by PEG-400 (CMP3) sample showed enhanced photocatalytic activity in comparison with the undoped samples.     

Optimization of PVD Parameters for the Deposition of Ultrahard Ti–Si–B–N Coatings

Multicomponent Ti–Si–B–N coatings were deposited on high-speed steel (HSS) substrates by reactive magnetron sputtering using a SHS TiB + 20 wt% Si target. The influences of the substrate temperature, bias voltage, and nitrogen partial pressure on the structure and the elemental compositions of the films were studied. The films were characterized by high-resolution transmission electron microscopy (HRTEM), Auger spectroscopy (AES), and X-ray diffraction (XRD). The results of HRTEM analysis indicated the formation of an ordered–disordered structure with fine crystalline grains of hexagonal Ti(B,N) _x phase and amorphous integrain layers. The stoichiometry of the Ti(B,N) _x phase was strongly affected by PVD process parameters. The films were characterized in terms of their microhardness and wear resistance. The reasons for the high value of microhardness appear to be the result of stoichiometric phase composition, compressive residual stress, and dense and fine microstructure of the Ti–Si–B–N coatings. The tribological wear test results indicated the superior wear-resistant properties of Ti–Si–B–N coatings compared to TiN and Ti(C,N) coatings.     

Optical propagation modified by Cu nanoparticle grating fabricated by heavy ion implantation

The optical propagation property of a planar waveguide with a periodic nanoparticle grating layer is characterized by using sliding prism method. Here, Cu nanoparticle grating was fabricated on a-SiO₂ substrate by periodic heavy-ion irradiation technique. The pitch of these gratings was 2 μm and 3 μm, respectively. The flux and fluence were at the range of 6-10 μA/cm² and 6 × 10¹⁶-1 × 10¹⁷ ions/cm², respectively. The grating effect, mainly including the mode selection effect, is observed. The effect depends on the pitch of the grating and the morphology of nanoparticles. The propagation loss of the waveguide induced by nanoparticle layer is evaluated.     

Effect of chopping on the properties of bismuth oxide thin films

Nanocrystalline bismuth oxide thin films have been deposited by thermal oxidation, in air, of vacuum evaporated chopped bismuth thin films. The optical properties and adhesion have been studied. The oxidation temperature and duration were varied. As revealed by structural investigations, polycrystalline and multiphase bismuth oxide thin films were obtained. At all oxidation temperatures, monoclinic Bi₂O₃ is predominant. The films showed high transmittance in the visible range of spectrum. The direct band gap of the films obtained was between 2.78 eV and 3.04 eV. The refractive index observed is in the range 1.934 to 2.096. The adhesion of films was in the range 215 × 10² to 470 × 10² kgF/cm². The values are strongly influenced by the heat treatment characteristics. It was observed that chopping helps in improving the adhesion and increasing refractive index, packing density and band gap of bismuth oxide thin films. These bismuth oxide films can have potential use in optical waveguides.     

Phosphorus-containing compounds of pollucite structure and radiochemical problems

New pollucite-like phosphorus-containing compounds with cesium and uni-, bi-, and trivalent cations (Li; Mg, Mn, Co, Ni, Cu, Zn, Cd, Sr, Ba; Al, Cr, Fe), many of which can be present in various combinations in wastes from radiochemical processes, were synthesized. The individual phases obtained were characterized by X-ray phase analysis and IR spectroscopy. The symmetry of the unit cells of the phosphorus-containing compounds decreases relative to the silicon analog (pollucite natural mineral) from Ia3d to I4₁32. The behavior of the compounds on heating to 1000°C, under hydrothermal conditions at 90°C, in aqueous systems (distilled water and seawater) at 25°C, and in a CsCl melt at 680°C was studied. The chemical and phase composition of the samples remained unchanged under all these conditions. The Cs leaching rates varied from 7.1 × 10⁻⁶ to 1.46 × 10⁻⁵ g cm⁻² day⁻¹. The “crystal-chemical modeling” of the new possible compositions of the compounds with the expected pollucite structure was performed.     

Fabrication and characterization of heat and plasma treated SiC/Al2O3-YSZ feedstocks used for plasma spraying

The SiC/Al₂O₃-YSZ (ZrO₂ + 8 wt.% Y₂O₃) powders with different SiC particle sizes were fabricated and treated from spray drying, heat treatment, and plasma spraying. The morphology, phase composition, flowability and density of powders were analyzed. The sphericity and flowability of powders treated by plasma flame are increased greatly, and the particle surface is very smooth. The flowability and density of powder with nano SiC were evident better than those of powder with submicron SiC. The optimum flowability and compactness of powder with submicron SiC is obtained when the critical plasma spray parameter is 341 and 325, respectively. For nano size SiC, the optimum flowability and the maximum compactness of powders are obtained with critical plasma spray parameter of 341. The grain size of powders is increased after heat treatment and plasma spraying. The SiC is oxidized to SiO₂ in the powders after heat treatment and plasma spraying. The Y₂O₃ dissolved from 8YSZ solid solution at higher critical plasma spray parameter. Besides, there is no phase transformation of ZrO₂ for powders. The metastable phase of Al₂O₃ appeared in feedstocks with submicron SiC, but no metastable phase was formed in feedstocks with nano SiC particles, which nano SiC can hinder the formation of Al₂O₃ metastable phase. The densification process and mechanism of reconstituted particles used for plasma spraying were analyzed from surface morphology, cross section and simulation.     

First-principles study of electronic and optical properties of Pbnm orthorhombic SrHfO3

The first-principles calculations were carried out to investigate the electronic and optical properties of Pbnm orthorhombic SrHfO₃. The equilibrium lattice constants of Pbnm orthorhombic SrHfO₃ optimized by the localized density approximation (LDA) are in good agreement with experimental values. Electronic structures of Pbnm orthorhombic SrHfO₃ have been studied throughout the calculations of band structure, densities of states (DOS) and charge densities. The band structure shows that Pbnm orthorhombic SrHfO₃ has direct band gap. The DOS and charge densities of Pbnm orthorhombic SrHfO₃ indicate that bonding between Hf and O is mainly covalent whereas bonding between Sr and O is mainly ionic. The complex dielectric function, refractive index, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of Pbnm orthorhombic SrHfO₃ have been predicted. The imaginary and real parts of the calculated complex dielectric function are consistent with the experimental measurements for the amorphous SrHfO₃.