Volume 32 (2014): Issue 4 (December 2014)

Factors influencing the reaction of chemical polymerization during aniline doping with hydrochloric acid (HCl) have been studied in this work. The optimal parameters for the preparation of polyaniline were determined as follows: aniline concentration - 4 mass %, molar ratios of oxidant (NH4)2S2O8:aniline - 1.2:1 and 1.3:1, the concentration of dopant - 1 mol/L. Fourier transform infrared spectroscopy (FT-IR) was applied to characterize the structure of polyaniline.

The paper investigates the properties of sodium zeolites synthesized using the hydrothermal method under autogenous pressure at low temperature with NaOH solutions of varying concentrations. During this modification, zeolites X, Na-P1 and hydroxysodalite were synthesized. The synthesis parameters, and thus, phase composition of resulting samples, significantly affected the specific surface area (SSA) and cation exchange capacity (CEC). SSA increased from 2.9 m2/g to a maximum of 501.2 m2/g, while CEC rose from 16 meq/100 g to a maximum of 500 meq/100 g. The best properties for use as a sorbent were obtained for perlite waste modified with 4.0 M NaOH at 70 °C or 80 °C.

An empirical network model has been developed to predict the in-plane thermal conductivities along arbitrary directions for unidirectional fiber-reinforced composites lamina. Measurements of thermal conductivities along different orientations were carried out. Good agreement was observed between values predicted by the network model and the experimental data; compared with the established analytical models, the newly proposed network model could give values with higher precision. Therefore, this network model is helpful to get a wider and more comprehensive understanding of heat transmission characteristics of fiber-reinforced composites and can be utilized as guidance to design and fabricate laminated composites with specific directional or specific locational thermal conductivities for structures that simultaneously perform mechanical and thermal functions, i.e. multifunctional structures (MFS).

Microstructural properties of Ce1-x GdxO2-δ (x = 0 to 0.3) thin films prepared by pulsed laser deposition technique were studied. The thin films were deposited on Si(100) substrate at a substrate temperature of 973 K at the oxygen partial pressure of 0.2 Pa using KrF excimer laser with energy of 220 mJ. The prepared thin films were characterized by X-ray diffraction, Raman spectroscopy and atomic force microscopy. X-ray diffraction analysis confirmed the polycrystalline nature of the thin films. Crystallite size, strain and dislocation density were calculated. The Raman studies revealed the formation of Ce-O with the systematic variation of peak intensity and full width half maxima depending on concentration of gadolinium dopant. The thickness of the films was estimated using Talystep profiler. The surface roughness was estiamted based on AFM.

The application of natural dyes extracted from plant seeds in the fabrication of dye-sensitized solar cells (DSSCs) has been explored. Ten dyes were extracted from different plant seeds and used as sensitizers for DSSCs. The dyes were characterized using UV-Vis spectrophotometry. DSSCs were prepared using TiO2 and ZnO nanostructured mesoporous films. The highest conversion efficiency of 0.875 % was obtained with an allium cepa (onion) extract-sensitized TiO2 solar cell. The process of TiO2-film sintering was studied and it was found that the sintering procedure significantly affects the response of the cell. The short circuit current of the DSSC was found to be considerably enhanced when the TiO2 semiconducting layer was sintered gradually.

Manganese dioxide (MnO2) films with different nanostructures were deposited on indium tin oxide (ITO) glasses by using chemical bath deposition (CBD). Deposition temperature and time were varied from 60 °C to 90 °C and from 2 h to 72 h, respectively. The samples have been characterized using an X-ray diffraction (XRD), field emission scanning electron microscope (SEM) and an electrochemical workstation. The films deposited at 60 °C for 8 h showed that obtained nanoflowers had an amorphous nature, while those deposited at higher temperatures of 70, 80 and 90 °C showed a well-developed nanowire and nanorod morphology. However, those which were deposited at 60 °C, showed the best electrochemical properties, including a higher specific capacitance, good rate of performance and a cycling stability (93 % loss of the initial value after 10,000 cycles).

Porous anodic aluminium oxide (AAO) template is commonly used in the synthesis of one-dimensional nanostructures, such as nanowires and nanorods, due to its simple fabrication process. Controlling the anodizing conditions is important because of their direct influence on the size of AAO template pores; it affects the size of nanostructures that are fabricated in AAO template. In present study, several alumina templates were fabricated by a two-step electrochemical anodization in different conditions, such as the time of first process, its voltage, and electrolyte concentration. The effect of these factors on pore diameters of AAO templates was investigated using scanning electron microscopy (SEM).

LiMn2O4 is an attractive candidate cathode material for Li-ion rechargeable batteries, but it suffers from severe capacity fading, especially at higher temperature (55 °C) during charging/discharging processes. Recently, many attempts have been made to synthesize modified LiMn2O4. In this work, a new study on the synthesis of pure and U4+-doped nano lithium manganese oxide [LiMn2−x UxO4, (x = 0:00, 0.01, 0.03)] via solid-state method was introduced. The synthesized LiMn1:97U0:03O4 was irradiated by γ-radiation (10 and 30 kGy). The green samples and the resulting spinel products were characterized using thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), infrared (IR), and scanning electron microscopy (SEM) measurements. XRD and SEM studies revealed nano-sized particles in all prepared samples. Direct-current (DC) electrical conductivity measurements indicated that these samples are semiconductors and the activation energies decrease with increasing rare-earth U4+ content and γ-irradiation. ΔEa equals to 0.304 eV for LiMn1:99U0:01O4, ΔEa is 0.282 eV for LiMn1:97U0:03O4 and decreases to ΔEa = 0:262 eV for γ-irradiated LiMn1:97U0:03O4 nano spinel. The data obtained for the investigated samples increase their attractiveness in modern electronic technology.

An implantable material based on titanium (Ti6Al4V) was sandblasted in order to be deposited with a thin film of hydroxyapatite. Two samples of the alloy, in a shape of a bar with 10 mm diameter and 20 mm length, were subjected to mechanical treatment. After deposition of the hydroxyapatite through electrophoresis process, the samples were analyzed by scanning electron microscopy. The nature and chemical properties of thin films formed on Ti-based substrate were investigated with electrochemical impedance spectroscopy based on the extremely high polarization resistance of the material. The results revealed the formation of a homogeneous layer on the surface of the metallic substrate. The layer composed of TiO2 and hydroxyapatite provided a high corrosion protection.

The paper presents a new model of the mechanism of mechanocatalysis and tribocatalysis. The reason for the increase in heterogeneous catalysis effect after mechanical activation of a catalyst has not been fully understood yet. There is no known theory, which would explain the mechanism of the influence of mechanical energy introduced to catalyst particles on the rate of chemical reaction. All existing theories are based on Arrhenius equation and assume that catalysts increase reaction rate due to decreasing of activation energy E a. We hypothesize that both for standard and catalyzed heterogeneous reactions the same E a (real activation energy) is needed to trigger the reaction processes and the catalytic effect is the result of energy introduced to the reaction system, its accumulation by a catalyst and then emission of high flux of energy to the space near the catalyst particles. This energy emitted by molecules of reagents can reach a value equal to the value of E a at lower ambient temperature than it would result from Arrhenius equation. This hypothesis is based on α i model described in previous papers by Kajdas and Kulczycki as well as the results of tribochemical research described by Hong Liang et al., which demonstrate that the reaction rate is higher than that resulting from temperature.

Tri-layer Au/Pd/Ni(P) films have been widely used as surface finish over the Cu pads in high-end packaging applications. It was found that a thin (Cu,Pd)6Sn5 IMC layer was beneficial in effective reducing inter-diffusion between a Cu substrate and a solder, and therefore the growth of the IMC layer and the EM (electromigration) processes. In this study, the structural properties and phase stability of monoclinic Cu6Sn5-based structures with Pd substitutions were studied by using the first-principles method. The (Cu,Pd)6Sn5 structure with the 4e site substituted by Pd has the lowest heat of formation and is the most stable among (Cu,Pd)6Sn5 structures. Hybridization of Pd-d and Sn-p states is a dominant factor for stability improvement. Moreover, Pd atoms concentration corresponding to the most stable structure of (Cu,Pd)6Sn5 was found to be 1.69 %, which is consistent with the experimental results.

(Na0.52K0.44Li0.04)0.97La0.01Ta0.20Nb0.80O3 (KNLTN-La0.01) lead-free subtransparent ceramics was prepared by a conventional sintering technique. The structure and the optical properties of the ceramics were investigated. The room temperature crystallographic indexing revealed the ABO3 perovskite type, tetragonal phase and P4mm point group in the ceramics. The surface and fractured surface SEM micrographs showed a dense microstructure with few micropores in KNLTN-La0.01 ceramics, which was obviously better than for the pure KNLTN ceramics. The refractive indexes of the films were investigated by an ellipsometer and the results show that the KNLTN-La0.01 subtransparent ceramics reveals significant wavelength dependent dispersion. The refractive index ranges from 2.14 to 2.06 with the wavelength increase from 380 nm to 900 nm. The dispersive behavior was analyzed by three parameters of Cauchy dispersion model and the values of the parameters A, B and C are 2.0610±0.0005, 0.0054±0.0003 and 0.00069±0.00004, respectively.

Results of optical-luminescence studies of polydoped photochromic CdBr2: AgCl,PbBr2 crystals are presented. It is shown that the luminescence decrease vs. time under N2-laser excitation in the range of A-band of Pb2+ absorption is due to photochemical reactions. The empirical model describing the decrease of the luminescence related to silver impurities due to photochemical processes is suggested. Model parameters (trapping cross-section — σ — and the amount of centres destroyed by irradiation — β) were determined using the comparative analysis of experimental and calculated luminescence decay curves.

A novel zinc porphyrin (5,10,15-tri-dodecoxyphenyl-20-(4-hydroxyphenyl-azo-benzenyl)-porphyrinatozinc (tdhab-ZnP)) with benzenyl-azo-phenolic group, able to adsorb on the nanocrystalline-TiO2 film, has been synthesized. We constructed a dye-sensitized solar cell based on the nanocrystalline-TiO2 hierarchical structure film, with a power conversion efficiency of 4.15 % and a high current density of 14 mA/cm2 under AM 1.5 irradiation. UV-Vis absorption spectra measurements indicated that the tdhab-ZnP molecules formed a charge transfer complex with TiO2 nanoparticles (NPs) through the phenolic group. Cyclic voltammetry measurement showed that the charge separation resulting from the tdhab-ZnP excited singlet state to the conduction band (CB) of TiO2 and charge shifting from the I−/I3− couple to the porphyrin radical cation were thermodynamically feasible.

Two titanium phosphate materials (TpP and ThP) have been successfully synthesized by sol-gel route with controlled precipitation and hydrolysis. The TpP material was obtained from the reaction between precipitated titania and phosphate buffer solution H2PO4− /HPO42− (pH = 7.3). The TpP material was prepared through hydrolysis of titanium in the presence of H2PO4−/HPO42. The probable state of the phosphate anions in titania framework and their effect on the anatase-to-rutile transformation were characterized by ICP-AES, DTA-TG, 31P NMR, FT-IR, and Raman analysis HRTEM/SEM. FT-IR and 31P NMR analyses of titanium phosphate TpP calcined at low temperature showed that the phosphate species existed not only as Ti-O-P in the bulk TiO2 but also as amorphous titanium phosphates, including bidentate Ti(HPO4)2 and monodentate Ti(H2PO4)4. Increased calcination temperature only gave an enrichment of bidentate structure on the titania surface. For the TpP material, H2PO4−/HPO42− anions were introduced into the initial solution, before precipitation, what promoted their lattice localization. At high temperatures, all the phosphorus inside the bulk of TiO2 migrated to the surface. The Raman analysis of both samples showed that the bidentate phosphates increased the temperature of the anatase-to-rutile phase transformation to more than 1000 °C with the formation of well crystalline TiP2O7 phase. This phenomenon was more evident for TpP sample.

Higher order elastic constants have been calculated in hexagonally structured superionic conductor Li3N at room temperature using the interaction potential model. The temperature variation of the ultrasonic velocities was evaluated along different angles with z axis (unique axis) of the crystal, using the second order elastic constants. The ultrasonic velocity decreased with the temperature along a particular orientation of the unique axis. Temperature variation of the thermal relaxation time and Debye average velocities was also calculated along the same orientation. The temperature dependency of ultrasonic properties was discussed in correlation with elastic, thermal and electrical properties. It has been found that the thermal conductivity is the main contributor to the behavior of ultrasonic attenuation as a function of temperature and the cause responsible for attenuation is phonon-phonon interaction. The mechanical properties of Li3N at low temperature are better than at high temperature because at low temperature it has low ultrasonic attenuation. Superionic conductor lithium nitride has many industrial applications, such as those used in portable electronic devices.

Monocrystalline fibres of undoped PrAlO3 and PrAlO3:0.1 Mn, have been grown by the pulling-down method under nitrogen atmosphere. The as-grown crystal doped with Mn had a visible brown core surrounded by a green ring, whereas this effect was weaker for the undoped PrAlO3. A coloration of the brown core was caused by a presence of Pr4+ ions. The presence of the Pr4+ ions was confirmed by XPS and magnetic studies. The XPS chemical analysis showed the increased concentration of oxygen in the crystals with the brown core. The most probable valency of manganese is Mn4+. It is located in Al3+ sites.

The thermal evolution of the interface formed by room temperature (RT) deposition of Ni atoms (coverage 0.1, 0.5, 1.2 ML) onto a Ge(111)-c(2 × 8) surface has been studied with the use of scanning tunneling microscopy (STM). Atomically resolved STM images revealed that, at RT, the boundaries between the different c(2 × 8) domains acted as nucleation sites for Ni atoms. After annealing the surface with deposited material at 473 to 673 K the formation of nano-sized islands of NixGey compounds was observed. In addition, the occurrence of ring-like structures was recorded. Based on the dual-polarity images the latter were assigned to Ni atoms adsorbed on Ge adatoms.

DBSA doped polypyrrole was prepared by In-situ chemical oxidative polymerization method. The reaction temperature was 0 to 20 °C. Different weight percentages of PSS (40 wt.%, 60 wt.% and 80 wt.%) were mechanically blended with a pestle in an agate mortar for 25 minutes by solid state mixing. The investigation of the blend focused on the optical, structural and morphological properties. SEM micrographs indicated that PSS was homogeneously distributed within DBSA doped PPy. FT-IR study confirmed the doped and blended dopants in the composite structure. UV-study revealed the π → π* transition in benzenoid rings of DBSA and presence of PSS. The semi-crystalline nature of the composites improved with increasing the weight percentage of PSS.

CdS and Zn-doped CdS (CdS:Zn) thin films have been deposited on glass substrates by spray pyrolysis technique using a perfume atomizer. The influence of Zn incorporation on the structural, morphological, optical and electrical properties of the films has been studied. All the films exhibit hexagonal phase with (0 0 2) as preferential orientation. A shift of the (0 0 2) diffraction peak towards higher diffraction angle is observed with increased Zn doping. The optical studies confirmed that the transparency increases as Zn doping level increases and the film coated with 2 at.% Zn doping has the maximum transmittance of about 90 %. The sheet resistance (Rsh) decreases as the Zn-doping level increases and a minimum value of 1.113 × 103 Ω/sq is obtained for the film coated with 8 at.% Zn dopant. The CdS film coated with 8 at.% Zn dopant has the best structural, morphological and electrical properties.

Physical properties of GexSb20−x Te80 (x = 11, 13, 15, 17, 19) bulk glassy alloys are examined theoretically. Lone pair electrons are calculated using an average coordination number (〈r〉) and the number of valence electrons, and are found to decrease with an addition of Ge. Mean bond energy (〈E〉) is proportional to glass transition temperature (Tg) and shows maxima near the chemical threshold. Cohesive energy of the system is calculated using chemical bond approach. A linear relation is found between cohesive energy, band gap (calculated theoretically and confirmed experimentally) and average heat of atomization. All these parameters are increasing with an increase in Ge content. A relation between average single bond energy and photon energy is discussed. Compactness of the structure is measured from the calculated density of the glass. An attempt is made to discuss the results in terms of structure of the glass or equivalently with average coordination number.

In this paper a novel method of SbSI single crystals fabrication is presented. In this method a sonochemically prepared SbSI gel is used as an intermediate product in a vapour growth process. The main advantages of the presented technique are as follows. First, the SbSI gel source material has lower temperature of sublimation and allows to avoid explosions during SbSI synthesis (the sonochemical synthesis is free of any explosion hazard). Second, but not least, the grown SbSI single crystals have smaller ratio of longitudinal and lateral dimensions. The cross sections of the presented crystals are relatively large (they are up to 9 mm2). The crystals have been characterized by X-ray diffraction, angle-resolved optical spectroscopy, and diffusive reflectivity.

The aim of the study was to determine the structure and hyperfine interactions of Bim+1Ti3Fem−3O3m+3 multiferroic Aurivillius compounds prepared by mechanical activation process. X-ray diffraction and Mössbauer spectroscopy were applied as complementary methods. After the process of mechanical milling, desired Aurivillius phases were not formed, thus, thermal treatment needed to be applied. Heating the product of mechanical activation up to 993 K allowed to obtain Aurivillius phases with relatively large amount of non-reacted hematite. However, after the material was annealed at an elevated temperature of 1073 K, the content of not fully synthesized hematite was significantly reduced. Mössbauer spectroscopy confirmed that Aurivillius compounds remain in paramagnetic state at room temperature.

A rapid, safe and simple technique for the production of high purity strontium oxide powders via a chemical combustion process is reported. The combustion reactions were performed to optimize the fuel to oxidizer ratios in the reaction mixtures required to obtain pure SrO powders by varying the molar ratio of chemical precursors and the temperature. The synthesized powders were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and N2-physisorption measurements. The results indicate that crystalline SrO was obtained using a 1:1 strontium nitrate: urea molar ratio at 1000 °C after 5 minutes. In addition, high-purity, homogeneous and crystalline SrO powders were easily produced in a short time via a chemical combustion process.

This paper describes the growth of Cd doped ZnO thin films on a glass substrate via sol-gel spin coating technique. The effect of Cd doping on ZnO thin films was investigated using X-ray diffraction (XRD), UV-Vis spectroscopy, photoluminescence spectroscopy, I–V characteristics and field emission scanning electron microscopy (FESEM). X-ray diffraction patterns showed that the films have preferred orientation along (002) plane with hexagonal wurtzite structure. The average crystallite sizes decreased from 24 nm to 9 nm, upon increasing of Cd doping. The films transmittance was found to be very high (92 to 95 %) in the visible region of solar spectrum. The optical band gap of ZnO and Cd doped ZnO thin films was calculated using the transmittance spectra and was found to be in the range of 3.30 to 2.77 eV. On increasing Cd concentration in ZnO binary system, the absorption edge of the films showed the red shifting. Photoluminescence spectra of the films showed the characteristic band edge emission centred over 377 to 448 nm. Electrical characterization revealed that the films had semiconducting and light sensitive behaviour.

Effect of different Sn contents on combustion synthesis of Ti2SnC was studied using elemental Ti, Sn, C and TiC powders as raw materials in the Ti-Sn-C and Ti-Sn-C-TiC system, in which the molar ratio of Ti/C was set as 2:1. The reaction mechanism for the formation of Ti2SnC was also investigated. The results showed that the amount of Ti2SnC in combustion products firstly increased with increasing of Sn content (0.6 to 0.8 mol), and then decreased with further increasing of Sn content (1.0 to 1.2 mol). Upon addition of 15 % TiC instead of Ti and C, the optimum addition of Sn decreased to 0.7 mol and a higher purity of Ti2SnC was obtained. The Ti2SnC powders were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Herein, we report a facile green synthesis of Cu2O nanoparticles (NPs) using copper sulfate as precursor salt and hydrazine hydrate as reducing agent in presence of bio-surfactant (i.e. leaves extract of arka — a perennial shrub) at 60 to 70 °C in an aqueous medium. A broad band centered at 460 nm in absorption spectrum reveals the formation of surfactant stabilized Cu2O NPs. X-ray diffraction pattern of the surfactant stabilized NPs suggests the formation of only Cu2O phase in assistance of a bio-surfactant with the crystallite size of ∼8 nm. A negative zeta potential of −12 mV at 8.0 pH in surfactant stabilized Cu2O NPs hints non-bonding electron transfer from O-atom of saponin to the surface of NP. Red-shift in the vibrational band (Cu-O stretching) of Cu2O from 637 cm−1 to 640 cm−1 in presence of bio-surfactant suggests an interfacial interaction between NPs and O-atoms of -OH groups of saponin present in the plant (i.e. Calotropis gigantean) extract. From X-ray photoelectron spectroscopy spectra, a decrease in binding energy of both 2p3/2 and 2p1/2 bands in Cu2O with saponin molecules as compared to bulk Cu atom reveals a charge transfer interaction between NP and saponin surfactant molecules. Transmission electron microscopy images show crystalline nature of Cu2O NPs with an fcc lattice.

Multi-walled carbon nanotubes have been synthesized at different temperatures ranging from 550 °C to 750 °C on silica supported Fe-Mo catalyst by chemical vapour deposition technique using Cymbopogen flexuous oil under nitrogen atmosphere. The as-grown MWNTs were characterized by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction analysis (XRD) and Raman spectral studies. The HRTEM and Raman spectroscopic studies confirmed the evolution of MWNTs with the outer diameter between 20 and 40 nm. The possibility of using as-grown MWNTs as an adsorbent for removal of As (V) ions from drinking water was studied. Adsorption isotherm data were interpreted by the Langmuir and Freundlich equations. Kinetic data were studied using Elovich, pseudo-first order and pseudo-second order equations in order to elucidate the reaction mechanism.

Structural, electronic and optical properties of MgxCd1−x Se (0 ≤ x ≤ 1) are calculated for the first time using density functional theory. Our results show that these properties are strongly dependent on molar fraction of particular components — x. The bond between Cd and Se is partially covalent and the covalent nature of the bond decreases as the concentration of Mg increases from 0 % to 100 %. It is found that MgxCd1−x Se has a direct band gap in the entire range of x and the band gap of the alloy increases from 0.43 to 2.46 eV with the increase in Mg concentration. Frequency dependent dielectric constants ɛ1(ω), ɛ2(ω) refractive index n(ω) are also calculated and discussed in detail. The peak value of refractive indices shifts to higher energy regions with the increase in Mg. The larger value of the extraordinary refractive index confirms that the material is a positive birefringence crystal. The present comprehensive theoretical study of the optoelectronic properties of the material predicts that it can be effectively used in optoelectronic applications in the wide range of spectra: IR, visible and UV. In addition, we have also predicted the heat capacities (CV), the entropy (S), the internal energy (U) and the Helmholtz free energy (F) of MgxCd1−x Se ternary alloys.

SnO2 nanocrystalline thin films have been deposited on oxidized silicon substrates by spin-coating from a precursor solution, followed by slow thermal annealing in oxygen atmosphere at different temperatures (500 to 900 °C). The precursor solution consisted of 1.0 to 2.0 M SnCl4·5H2O in isopropanol. It was shown that the concentration of the precursor solution, annealing temperature and heating rate had a significant effect on the structural, optical and electrical properties of the studied thin films. The topography of SnO2 thin films was examined by scanning electron microscopy (SEM). Furthermore, as-deposited films were characterized by X-ray diffraction (XRD), UV-Vis and impedance spectroscopy.