• Volume 36, Issue 4

August 2013,   pages  505-764

• Preparation and gas-sensing property of parallel-aligned ZnO nanofibrous films

Parallel-aligned zinc oxide (ZnO) nanofibrous films fabricated by using electrospinning technique were used in gas sensors for the detection of ethanol and formaldehyde. The morphologies and crystal structures of the films were characterized by field-emission scanning electron microscopy (FE–SEM) and X-ray diffraction (XRD), respectively. FE–SEM results showed that ZnO nanofibres had an approximate diameter of 100–300 nm and consisted of hexagonal wurtzite structure ZnO nanocrystals with a primary particle diameter of 20–50 nm. The results of resistance–temperature characteristics and responses to ethanol and formaldehyde indicated that the parallelaligned ZnO nanofibrous film had a low activation energy (0.246 eV), a low optimum operating temperature and a high response. The response and recovery had a high rate in the initial stage and a low rate in the later stage. The parallel-aligned ZnO nanofibrous film had excellent potential application for formaldehyde sensor.

• Synthesis and up-conversion luminescence of Yb3+–Ho3+ co-doped Na(Y1.5Na0.5)F6 nanorods

We present the optical up-conversion (UC) study for Yb3+–Ho3+ co-doped Na(Y1.5Na0.5)F6 nanorods synthesized by employing a facile hydrothermal method. Numbers of Ho3+ ion up-conversion emissions have been observed under 980 nm infrared diode laser excitation. Three UC emissions of interest, ultraviolet, violet and blue, are specially identified at 359, 387, 418 and 483 nm, corresponding to ${}^{5}G'_{5}/{}^{3}H_{6} \rightarrow {}^{5}I_{8}, {}^{5}G_{4}/{}^{3}K_{7} \rightarrow {}^{5}I_{8}, {}^{5}G_{5} \rightarrow {}^{5}I_{8}$ and ${}^{5}F_{3}/{}^{5}F_{2}/{}^{3}K_{8} \rightarrow {}^{5}I_{8}$ transitions, respectively. It is also found that the centre wavelength of blue UC emission shifts to 475 nm gradually as Ho3+ concentration decreases. Lastly, a brief analysis about UC mechanism is demonstrated according to the experimental results.

• Dependence of thermal conductivity in micro to nano silica

This work presents the measurement of thermal conductivity of nano-silica particles using needle probe method. The validation test of thermal probe was conducted on ice and THF hydrates using our experimental set up and the results are satisfactory when compared with the literature data. The nano silica used in this study is with particle sizes in the range 50–1000 nm. The sand powders sieved in different sizes &lt;75 and 75 𝜇m &gt; 𝑑 &gt; 250 𝜇m were also studied to probe the particle size dependence on thermal conductivity. Thermal conductivity decreased by about 70% in silica nano powders.

• Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method

Pure and fluorine-modified tin oxide (SnO2) thin films (250–300 nm) were uniformly deposited on corning glass substrate using sol–gel technique to fabricate SnO2-based resistive sensors for ethanol detection. The characteristic properties of the multicoatings have been investigated, including their electrical conductivity and optical transparency in visible IR range. Pure SnO2 films exhibited a visible transmission of 90% compared with Fdoped films (80% for low doping and 60% for high doping). F-doped SnO2 films exhibited lower resistivity (0.12 × 10-4𝛺 cm) compared with the pure (14.16 × 10-4𝛺 cm) one. X-ray diffraction and scanning electron microscopy techniques were used to analyse the structure and surface morphology of the prepared films. Resistance change was studied at different temperatures (523–623 K) with metallic contacts of silver in air and in presence of different ethanol vapour concentrations. Comparative gas-sensing results revealed that the prepared F-doped SnO2 sensor exhibited the lowest response and recovery times of 10 and 13 s, respectively whereas that of pure SnO2 gas sensor, 32 and 65 s, respectively. The maximum sensitivities of both gas sensors were obtained at 623 K.

• Synthesis of copper telluride nanowires using template-based electrodeposition method as chemical sensor

Copper telluride (CuTe) nanowires were synthesized electrochemically from aqueous acidic solution of copper (II) sulphate (CuSO4.5H2O) and tellurium oxide (TeO2) on a copper substrate by template-assisted electrodeposition method. The electrodeposition was conducted at 30 °C and the length of nanowires was controlled by adjusting deposition time. Structural characteristics were examined using X-ray diffraction and scanning electron microscope which confirm the formation of CuTe nanowires. Investigation for chemical sensing was carried out using air and chloroform, acetone, ethanol, glycerol, distilled water as liquids having dielectric constants 1, 4.81, 8.93, 21, 24.55, 42.5 and 80.1, respectively. The results unequivocally prove that copper telluride nanowires can be fabricated as chemical sensors with enhanced sensitivity and reliability.

• Effect of nano-CeO2 on microstructure properties of TiC/TiN+TiCN-reinforced composite coating

TiC/TiN+TiCN-reinforced composite coatings were fabricated on Ti–6Al–4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO2 was able to suppress crystallization and growth of crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO2, this coating exhibited fine microstructure. In this study, Al3Ti+TiC/TiN+nano-CeO2 laser-cladded coatings have been studied by means of X-ray diffraction and scanning electron microscope. X-ray diffraction results indicated that Al3Ti+TiC/TiN+nano-CeO2 laser-cladded coating consisted of Ti3Al, TiC, TiN, Ti2Al20Ce, TiC0.3N0.7, Ce(CN)3 and CeO2, this phase constituent was beneficial in increasing microhardness and wear resistance of Ti–6Al–6V alloy.

• Composite supercapacitor electrodes made of activated carbon/PEDOT:PSS and activated carbon/doped PEDOT

In this paper, we report on the high electrical storage capacity of composite electrodes made from nanoscale activated carbon combined with either poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) or PEDOT doped with multiple dopants such as ammonium persulfate (APS) and dimethyl sulfoxide (DMSO). The composites were fabricated by electropolymerization of the conducting polymers (PEDOT:PSS, doped PEDOT) onto the nanoscale activated carbon backbone, wherein the nanoscale activated carbon was produced by ball-milling followed by chemical and thermal treatments. Activated carbon/PEDOT:PSS yielded capacitance values of 640 F g-1 and 26mF cm-2, while activated carbon/doped PEDOT yielded capacitances of 1183 F g-1 and 42 mF cm-2 at 10 mV s-1. This is more than five times the storage capacity previously reported for activated carbon–PEDOT composites. Further, use of multiple dopants in PEDOT improved the storage performance of the composite electrode well over that of PEDOT:PSS. The composite electrodes were characterized for their electrochemical behaviour, structural and morphological details and electronic conductivity and showed promise as high-performance energy storage systems.

• Characterization of molybdenum-doped indium oxide thin films by spray pyrolysis technique

In this research, indium oxide nanostructure undoped and doped with Mo were prepared on glass substrates using spray pyrolysis technique. Various parameters such as dopant concentration and deposition temperatures were studied. Structural properties of these films were investigated by X-ray diffraction and scanning electron microscopy. Electrical and optical properties have been studied by Hall effect and UV–Visible spectrophotometer, respectively. The thickness of the films was determined by PUMA software. The variation of refractive index, extension coefficient and bandgap of these films also were investigated.

• Low-field magnetization process and complex permeability of FeCoBSiTa wires coated with hard magnetic CoNi layer

Biphase wires consisting of a soft magnetic amorphous nucleus surrounded by a hard magnetic CoNi layer of variable thickness were obtained by means of rotating water-quenching method and subsequent electroplating technique. Magnetization processes for all the biphase wires were resolved in terms of reversible bulging of magnetic domains and spin rotation by means of complex permeability measurements within the frequency range of 10 Hz–13 MHz. Results are interpreted in terms of CoNi layer effect on the magnetic anisotropy of the soft core.

• Sulfonated carbon black-based composite membranes for fuel cell applications

Two different commercial grade carbon black samples, Cabot Regal 400R (C1) and Cabot Mogul L (C2), were sulfonated with diazonium salt of sulfanilic acid. The resultant sulfonated carbon black samples (S–C) were characterized by Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Composite membranes were then prepared using S–C as fillers and sulfonated poly(ether ether ketone) (SPEEK) as polymer matrix with three different sulfonation degrees (DS = 60, 70 and 82%). Structure and properties of the composite membranes were characterized by FTIR, TGA, scanning electron microscopy, proton conduction, water uptake, ion exchange capacity and chemical stability. Incorporation of S–C particles above 0.25 wt% caused decrease in chemical stability. Pristine and composite membranes prepared from SPEEK82 decomposed completely in &lt;1 h, which is undesirable for fuel cell applications. SPEEK60 membrane having wt% of 0.25–0.5 with S–C particles led to higher proton conductivity than that of pristine membrane. No positive effect was observed on the properties of the composite membranes with the addition of S–C particles at high concentrations due to the agglomeration problems and decrease in the content of conductive polymer matrix.

• Optimization of mechanical properties of non-woven short sisal fibre-reinforced vinyl ester composite using factorial design and GA method

This work presents a systematic approach to evaluate and study the effect of process parameters on tensile, flexural and impact strength of untreated short sisal fibre-reinforced vinyl ester polymer-based composites and predicts the optimum properties of random natural fibre-reinforced composites. The natural fibre of sisal at lengths of 10, 30 and 50 mm and vinyl ester resin at loadings of 15, 30 and 45 (wt%) were prepared. The composite panel was then fabricated using hand lay method in cold process of size 180 × 160 mm2. Samples were then cut from the panel and subjected to mechanical properties testing such as tensile, flexural and impact strengths. The average tensile strength ranges between 27.1 and 43.9 MPa. The flexural strength ranged between 26.9 and 49.5 MPa and the impact strength ranged between 16 and 93 J/m. The strength values were optimized using factorial design and genetic algorithm (GA) method. The predicted optimum process parameter values are in good agreement with the experimental results.

• Graphene composites containing chemically bonded metal oxides

Composites of graphene involving chemically bonded nano films of metal oxides have been prepared by reacting graphene containing surface oxygen functionalities with metal halide vapours followed by exposure to water vapour. The composites have been characterized by electron microscopy, atomic force microscopy and other techniques. Magnetite particles chemically bonded to graphene dispersible in various solvents have been prepared and they exhibit fairly high magnetization.

• Impedance and a.c. conductivity studies of Ba(Pr1/2Nb1/2)O3 ceramic

Impedance and electrical conduction studies of Ba(Pr1/2Nb1/2)O3 ceramic prepared through conventional ceramic fabrication technique are presented. The crystal symmetry, space group and unit cell dimensions were estimated using Rietveld analysis. X-ray diffraction analysis indicated the formation of a single-phase cubic structure with space group, 𝑃𝑚$\bar{3}$𝑚. EDAX and SEM studies were carried out to study the quality and purity of compound. To find a correlation between the response of the real system and idealized model circuit composed of discrete electrical components, the model fittings were presented using impedance data. Complex impedance as well as electric modulus analyses suggested dielectric relaxation to be of non-Debye type and negative temperature coefficient of resistance character. The correlated barrier hopping model was employed to successfully explain the mechanism of charge transport in Ba(Pr1/2Nb1/2)O3. The a.c. conductivity data were used to evaluate density of states at Fermi level, minimum hopping length and apparent activation energy.

• Investigation on microstructure and dielectric behaviour of (Ba0.999−𝑥Gd0.001Cr𝑥)TiO3 ceramics

Ceramics of BaTiO3 co-doped with Gd and Cr at Ba-site was synthesized via solid-state reaction route. Surface morphology shows the increase in grain size with the increase of Cr-content below 3 mol%. The high value of 𝜀 in the synthesized samples is associated with space charge polarization and inhomogeneous dielectric structure. Gd is diffused well into the most of Ba sites and vacancies leaving very few defects or voids for the generation of absorption current which results in dielectric loss. Below 3 mol% of Cr-concentration, dissipation factor was improved. Increase in a.c. conductivity with rise of temperature is due to increase in thermally activated electron drift mobility of charges according to the hopping conduction mechanism. Moreover, samples show the positive temperature coefficient of conductivity, which is most desirable for developing highly sensitive thermal detectors and sensors. Also, higher frequency indicates motion of charges in the ceramic samples.

• Low-energy excitations in a low-viscous glass-forming liquid

Polarized and depolarized low frequency Raman spectra of a liquid mixture, viz. 0.15LiCl–0.85H2O, has been analysed in detail in order to elucidate the temperature and polarization characteristics of quasi-elastic line and Boson peak. The employed fitting procedure shows more convincingly that the Boson peak contribution to the overall low frequency Raman pattern is present even in this low-viscous liquid. The degree of disorder in this liquid is not so high and certain micro-ordering effects may take place due to hydrogen bonding. The results are discussed in the framework of the current phenomenological status of the field.

• Role of aluminium addition on structure of Fe substituted Fe73.5−𝑥Si13.5B9Nb3Cu1Al𝑥 alloy ribbons

The investigation has dealt with the structure and magnetic properties of rapidly solidified and annealed Fe73.5−𝑥Si13.5B9Nb3Cu1Al𝑥 (𝑥 = 0, 2, 4, 6 at%) ribbons prepared by melt spinning. Complete amorphous structure was obtained in as-spun ribbons of 𝑥 = 0 and 2 at% compositions, whereas structure of ribbons containing higher Al was found to be partially crystalline. Detailed thermal analyses of the alloys and the melt spun ribbons revealed that the glass forming ability in the form of 𝑇x/𝑇l (ratio between crystallization and liquidus temperature) is the highest for 2 at% Al alloys and decreases with further addition of Al. Annealing of all as spun ribbons resulted in the precipitation of nanocrystalline phase embedded in amorphous matrix in the form of either 𝐷𝑂3 phase or 𝑏𝑐𝑐 𝛼-Fe(Si/Al) solid solution depending on the initial composition of the alloy. Only 𝑏𝑐𝑐 𝛼-Fe(Si/Al) solid solution was formed in 2 at% Al ribbons whereas ordered DO3 structure was found to be stabilized in other ribbons including 0 at% Al. A detailed study on determination of precision lattice parameter of nanocrystalline phase revealed that the lattice parameter increases with the addition of Al indicating the partitioning behaviour of Al in nanocrystalline phase.

• Investigation of localization effect in GaN-rich InGaN alloys and modified band-tail model

The temperature-dependent PL properties of GaN-rich In𝑥Ga1−𝑥N alloys is investigated and 𝑆-shaped temperature dependence is observed in all InGaN samples. It is found that the origin of localization effect in samples A and B are different from that in sample C. For samples A and B, In content fluctuations should be the origin of localization effect, while the localization effect can be attributed to In-rich clusters and metallic indium inclusions for sample C. In addition, the band-tail model is modified and the modified band-tail model is used to investigate the degree of localization effect in the three samples.

• Effect of temperature and displacement rate on behaviour of as-cast AA5182 and Al–3.3%Cu alloys under tensile loading near solidus temperature

Hot cracking develops in the still semi-solid casting during the last stages of solidification. The micromechanism of its origin is not generally accepted. There exists considerable doubt whether it is initiated by a void or develops as an instantaneous crack. The aim of this work is to study the mechanism of fracture behaviour of aluminum alloys around solidus temperature. Tensile tests were performed on notched specimens of as-cast AA5182 and Al–3.3%Cu alloys using a Gleeble 3500® thermomechanical simulator. The effect of temperature and strain rate on the propagation of fracture in the semi-solid state has been studied to establish fracture mechanism. The transition from ductile to brittle mode of fracture has been observed around the solidus temperature. The fracture is intergranular and propagates through interdendritic channels.

• Effect of plasticizer and fumed silica on ionic conductivity behaviour of proton conducting polymer electrolytes containing HPF6

The effect of addition of propylene carbonate (PC) and nano-sized fumed silica on the ionic conductivity behaviour of proton conducting polymer electrolytes containing different concentrations of hexafluorophosphoric acid (HPF6) in polyethylene oxide (PEO) has been studied. The addition of PC results in an increase in ionic conductivity, whereas the addition of nano-sized fumed silica improves mechanical strength of electrolytes along with a small increase in ionic conductivity. It was observed that the simultaneous addition of PC and fumed silica results in electrolytes with optimum value of ionic conductivity and other properties.

• Conductivity study of solid polyelectrolytes based on hydroiodide salt of poly(4-vinyl pyridine-co-butylmethacrylate), poly(4-vinyl pyridine-co-butylacrylate)

The chain flexibility of poly(4-vinylpyridine) was tried to increase by lowering its glass transition temperature (𝑇g) and by increasing its amorphous region by copolymerizing with butyl methacrylate and butylacrylate which act as internal plasticizer. The copolymers were prepared in five different feed molar ratios to optimize the required properties such as higher room temperature conductivity and better film-forming capacity. The conductivity and conduction behaviour of the copolymers, as well as their hydroiodide salts have been reported. There was about 103–104-fold increase in room temperature conductivity of these plasticized polyelectrolytes.

• Poly(aniline-co-𝑚-aminobenzoic acid) deposited on poly(vinyl alcohol): Synthesis and characterization

In this work, we have deposited poly(aniline-co-𝑚-aminobenzoic acid) on poly(vinyl alcohol) (PVA) by in situ polymerization. The polymerization was effected within maleic acid (MA) cross-linked PVA hydrogel. The copolymer was obtained by oxidative polymerization of aniline hydrochloride and 𝑚-aminobenzoic acid using ammonium persulfate as an oxidant. Instead of conventional solution polymerization, here synthesis was carried out on APS soaked MA cross-linked PVA (MA–PVA) film where the polymer was in situ deposited in its conducting form. The composite film was characterized by Fourier transform infra red (FT–IR) and ultraviolet visible (UV–VIS) spectroscopy and electrical measurements. Surface morphology of the composite films was studied by field emission scanning electron microscopy (FESEM). The variation of conductivity of the films was studied.

• Impact of interfacial interactions on optical and ammonia sensing in zinc oxide/polyaniline structures

Zinc oxide/polyaniline (ZnO/PANI) hybrid structures have been investigated for their optical and gas sensing properties. ZnO nanoparticles, prepared by the sol–gel method, pressed in the form of pellets were used for gas sensing. The hybrid ZnO/PANI structure was obtained by the addition of PANI on the surface of ZnO. The UV–Vis absorption of the modified pellets show band edge at 363 nm corresponding to ZnO, while a change in the absorption peaks for PANI was observed. The possible interaction between Zn2+ of ZnO and NH-group of PANI was confirmed using Raman spectroscopy studies. The results reveal that the hybrid structures exhibit much higher sensitivity to NH3 gas at room temperature than blank ZnO, which is sensitive to NH3 gas at higher temperature. This enhancement has been attributed to the creation of active sites on the ZnO surface due to the presence of PANI.

• Processing and performance of organic insulators as a gate layer in organic thin film transistors fabricated on polyethylene terephthalate substrate

Fabrication of organic thin film transistor (OTFT) on flexible substrates is a challenge, because of its low softening temperature, high roughness and flexible nature. Although several organic dielectrics have been used as gate insulator, it is difficult to choose one in absence of a comparative study covering processing of dielectric layer on polyethylene terephthalate (PET), characterization of dielectric property, pentacene film morphology and OTFT characterization. Here, we present the processing and performance of three organic dielectrics, poly(4-vinylphenol) (PVPh), polyvinyl alcohol (PVA) and poly(methylmethacrylate) (PMMA), as a gate layer in pentacene-based organic thin film transistor on PET substrate. We have used thermogravimetric analysis of organic dielectric solution to determine annealing temperature for spin-coated films of these dielectrics. Comparison of the leakage currents for the three dielectrics shows PVA exhibiting lowest leakage (in the voltage range of −30 to +30 V). This is partly because solvent is completely eliminated in the case of PVA as observed by differential thermogravimetric analysis (DTGA). We propose that DTGA can be a useful tool to optimize processing of dielectric layers. From organic thin film transistor point of view, crystal structure, morphology and surface roughness of pentacene film on all the dielectric layers were studied using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM).We observe pyramidal pentacene on PVPh whereas commonly observed dendritic pentacene on PMMA and PVA surface. Pentacene morphology development is discussed in terms of surface roughness, surface energy and molecular nature of the dielectric layer.

• Hydriding and dehydriding rates and hydrogen-storage capacity of Mg–14Ni–3Fe2O3–3Ti prepared by reactive mechanical grinding

The magnesium prepared by mechanical grinding under H2 (reactive mechanical grinding) with transition elements or oxides showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt%. Ni (expected to increase hydriding and dehydriding rates) was chosen as transition element to be added. Fe2O3 (expected to increase hydriding rate) was selected as an oxide to be added. Ti was also selected since, it was considered to increase the hydriding and dehydriding rates by forming Ti hydride. A sample, Mg–14Ni–3Fe2O3–3Ti, was prepared by reactive mechanical grinding and its hydrogen storage properties were investigated. This sample absorbed 4.02 wt% H for 5 min, 4.15 wt% H for 10 min and 4.42 wt% H for 60 min at 𝑛 = 2. It desorbed 2.46 wt% H for 10 min, 3.98 wt% H for 30 min and 4.20 wt% H for 60 min at 𝑛 = 2.

• Combustion synthesis of graphene and ultracapacitor performance

Graphene sheets are synthesized by a simple method starting from graphitic oxide as a precursor. Reaction of graphitic oxide at 250 °C with a combustion mixture of urea and ammonium nitrate results in the formation of thin graphene sheets. Graphene formation is characterized by XRD, TGA, XPS and TEM. Graphene materials synthesized by thismethod are investigated as an ultracapacitor material. Specific capacitance values of about 70 F/g are obtained at a current density of 100 mA/g by usingKOH as an electrolyte.

• Combustion reaction of Ti–Al–C–N system

The combustion reaction of Ti–Al–C–N system was investigated by using Ti powders and one CN𝑥 precursor powder as reactant powder blends. The reactant powder blends ratio was adjusted to obtain different materials. The phase composition of the samples was investigated by X-ray diffraction (XRD). The microstructure of the samples was observed by scanning electron microscopy (SEM). The result showed that Ti2Al(C,N)–TiAl𝑥, AlN–Ti(C,N) and Ti3Al(C,N)2–TiC composites can be fabricated by changing the reactant powder blends ratio.

• Mobilities and dislocation energies of planar faults in an ordered A3B (D019) structure

Present work describes the stability of possible planar faults of the A3B (D019) phase with an axial ratio less than the ideal. Mobilities and dislocation energies of various planar faults viz. antiphase boundaries (APBs), superlattice intrinsic stacking faults (SISFs) and complex stacking faults (CSFs) have been computed using complex fourth-order tensor transformations and hard sphere model. Displacements normal to the slip planes for various slip systems (vertical shift) have been used to calculate mobility of dislocations. The energy of the planar faults in Ti3Al intermetallic is calculated using some simplifying assumptions. Based on the mobility and energy, stability of planar faults has been explained. These results are compared with single crystal ordered Ti3Al alloy having D019 structure.

• Enhanced high temperature performance of LiMn2O4 coated with Li3BO3 solid electrolyte

Cathode material, LiMn2O4, was synthesized by solid-state reaction followed by surface coating of Li3BO3 solid electrolyte. Structure and electrochemical performance of the prepared powders were characterized by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge techniques, respectively. Results show that Li3BO3 coated LiMn2O4 has similar X-ray diffraction patterns as LiMn2O4. The discharge specific capacities of LiMn2O4 coated with 0.1, 0.3 and 0.6 wt% Li3BO3 are 123.3, 118.2 and 110 mAh/g, respectively, which is slightly smaller than that of 124.4 mAh/g for LiMn2O4. However, the capacity retention of Li3BO3 coated LiMn2O4 is at least 5.6 and 7.6% higher than LiMn2O4 when cycled at room temperature and 55 °C, respectively. Li3BO3 coated LiMn2O4 shows much better cycling behaviours than LiMn2O4.

• Phase transitions and their co-existence in TlGaSe2–TlCrS2(Se2) systems

Investigation of dielectric properties of layered compound, TlGaSe2, showed that it is a ferroelectric (𝑇c = 105.5 K) with an intermediate incommensurate phase (𝑇i = 114.5 K). Our magnetic studies of layered compounds, TlCrS2 and TlCrSe2, for the first time revealed that the magnetic phase transition in these compounds are quasi two-dimensional ferromagnetic in nature and magnetic characteristics are 𝑇c = 90 K, $T^{p}_{C}$ = 115 K, 𝜇eff = 3.26 𝜇B and 𝑇c = 105 K, $T^{p}_{C}$ = 120 K, 𝜇eff = 3.05 𝜇B, respectively. Using the method of DTA, areas of homogeneous and heterogeneous coexistence of ferroelectric and ferromagnetic phase transitions in the systems, TlGaSe2–TlCrS2 and TlGaSe2–TlCrSe2, were identified. The low-dimensional solid solutions and eutectic alloys in these systems can be used as basic materials for plenty of functional recorders.

• Rietveld analysis, dielectric and impedance behaviour of Mn3+/Fe3+ ionmodified Pb(Zr0.65Ti0.35)O3 perovskite

The polycrystalline samples of Pb(Zr0.65−𝑥A𝑥Ti0.35)O3 (A = Mn/Fe), (𝑥 = 0.00, 0.05) (PZM/FT) were synthesized by conventional solid-state reaction technique. X-ray diffraction (XRD) pattern was recorded at room temperature and the samples were found in single phase form. All the observed peaks could be indexed to 𝑅3𝑐 space group with rhombohedral symmetry. XRD pattern has been analysed by employing Rietveld method with the help of FullProf Program. The lattice parameters and unit cell volumes decrease from Mn3+ to Fe3+ ion concentrations. The bond lengths and angles have been calculated by using Powder Cell Programme. Microstructural analysis of the surface of the ceramic compound by scanning electron microscopy (SEM) exhibits that there is a significant change in grain size on introduction of Mn3+ and Fe3+ ions at the Zr-site of the compound. It is observed that both the substitutions (Mn3+ and Fe3+) at Zr site induce an increase in dielectric constant and a shift in Curie temperature (𝑇c). From a.c. conductivity analysis, we have estimated the activation energy for both ferroelectric and paraelectric regions. Both the modified samples are obeying Jonscher power law. From Nyquist plots, the activation energy of grain resistance, relaxation time and bulk conductivity are compared. The grain resistance of the material decreases with rise in temperature which indicates a semiconducting behaviour of the material.

• On grain growth kinetics in two-phase polycrystalline materials through Monte Carlo simulation

Monte Carlo Potts model simulation was carried out on a 2D square lattice for various surface fractions of second phase particles for over 50,000 iterations. The observations are in good agreement with known theoretical and experimental results with respect to both growth kinetics as well as grain size distribution. Further, the average grain size and the largest grain size were computed for various surface fractions which have indicated normal grain growth and microstructure homogeneity. The surface fraction of the second phase particles interacting with the grain boundaries (𝛷), hitherto not computed through the simulation route, is shown to vary inversely as the average grain size due to Zener pinning.

• Photoluminescence properties of X5SiO4Cl6:Tb3+ (X = Sr, Ba) green phosphor prepared via modified solid state method

Luminescence property of a new halo silicate phosphor, X5SiO4Cl6:Tb3+ (X = Sr, Ba) prepared by modified solid state method is reported here. It is characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. In the emission spectra of X5SiO4Cl6:Tb3+ (X = Sr, Ba) phosphor, characteristic blue and green emission peaks are present corresponding to Tb3+ intra 4𝑓 transition. Emission spectrum shows a dominant peak at 544 nm due to the ${}^{5}D_{4} \rightarrow {}^{7}F_{5}$ transition of Tb3+.

• Effect of plating time on growth of nanocrystalline Ni–P from sulphate/glycine bath by electroless deposition method

Nanocrystalline nickel phosphorus (NC-Ni–P) deposits from sulphate/glycine bath using a simple electroless deposition process is demonstrated. In the present investigation, nanoporous alumina films are formed on the aluminium surface by anodization process followed by deposition of nickel onto the pores by electroless plating method. Anodic aluminium oxide surface was first sensitized and activated by using palladium chloride solution before immersing into the electroless nickel bath. Electroless nickel plating was carried out from the optimized bath by changing the deposition time from 20 to 1800 s at a constant temperature of 80 °C and a pH of 4.0. Surface morphology, elemental composition, structure and reflectance of the deposits have been analysed by using scanning electron microscopy, atomic force microscopy, energy dispersive X-ray analysis, X-ray diffractometry and UV-visible spectroscopic studies, respectively. Electroless nickel deposits formed at an early stage produces dense uniform nanocrystals containing higher percentage of atomic phosphorus with cubic Ni (111) structure. As the deposition time increased, nanocrystalline sharp peak became amorphous and dimension of the crystal size varied from 54 to 72 nm.

• Studies on electrical double layer capacitor with a low-viscosity ionic liquid 1-ethyl-3-methylimidazolium tetracyanoborate as electrolyte

The performance of an electrical double layer capacitor (EDLC) composed of high surface area activated carbon electrodes and a new ionic liquid, 1-ethyl-3-methylimidazolium tetracyanoborate, [EMIm]TCB, as the electrolyte has been investigated by impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge studies. The high ionic conductivity (∼1.3 × 10-2 S cm-1 at 20 °C) and low viscosity (∼22 cP) of the ionic liquid, [EMIm]TCB, make it attractive as electrolyte for its use in EDLCs. The optimum capacitance value of 195.5 F g-1 of activated carbon has been achieved with stable cyclic performance.

• Effect of electrodeposition potential on composition and morphology of CIGS absorber thin film

CuInGaSe (CIGS) thin films were deposited on Mo/soda-lime glass substrates by electrodeposition at different potentials ranging from −0.3 to −1.1 V vs Ag/AgCl. Cyclic voltammetry (CV) studies of unitary Cu, Ga, In and Se systems, binary Cu–Se, Ga–Se and In–Se systems and quaternary Cu–In–Ga–Se were carried out to understand the mechanism of deposition of each constituent. Concentration of the films was determined by energy dispersive spectroscopy. Structure and morphology of the films were characterized by X-ray diffraction and scanning electron microscope. The underpotential deposition mechanism of Cu–Se and In–Se phases was observed in voltammograms of binary and quaternary systems. Variation in composition with applied potentials was explained by cyclic voltammetry (CV) data. A suitable potential range from −0.8 to −1.0 V was found for obtaining films with desired and stable stoichiometry. In the post-annealing films, chalcopyrite structure starts forming in the samples deposited at −0.5 V and grows on varying the applied potential towards negative direction. By adjusting the composition of electrolyte, we obtained the desired stoichiometry of Cu(In0.7Ga0.3)Se2.

• Investigation of superhalogen behaviour of RuF𝑛 (𝑛 = 1–7) clusters: density functional theory (DFT) study

In the present investigation, interaction of ruthenium (Ru) atoms with fluorine (F) atoms was studied using the density functional theory utilizing B3LYP method. It was found that up to seven F atoms can bind to a single Ru atom which results in increase of electron affinities successively, reaching a peak value of 6.95 eV for RuF6. Its stability and reactivity were also examined by using HOMO–LUMO gap, molecular orbital analysis and binding energy of these clusters. It is found that energy required for dissociation of F2 molecules are higher than energy required for dissociation of F atoms. The unusual properties are attributed to the involvement of inner shell 4𝑑-electrons, which not only allow RuF𝑛 clusters to belong to the class of superhalogens but also show that its valence can exceed the nominal value of 1. The interaction of RuF4 superhalogen with an alkali atom lithium (Li) were also studied which suggests that a new class of salt can be synthesized by reacting RuF4 with Li.

• Magnetic resonance in superparamagnetic zinc ferrite

In the present work, we have synthesized zinc ferrite nanoparticles by nitrate method. Presence of almost zero value of coercivity and remanence in the hysteresis of these samples shows the superparamagnetic nature at room temperature. Electron paramagnetic resonance spectroscopy performed on these samples in the temperature range 120–300 K indicates the systematic variation of the line-shapes of the spectra with temperature. Both gvalue and peak-to-peak linewidth decrease with increase in temperature. The variation of g-values and peak-topeak linewidth with temperature has been fitted with existing models and we observed different values of activation energies of the spins for both the samples.

• Effect of calcination conditions of pork bone sludge on behaviour of hydroxyapatite in simulated body fluid

The paper presents in vitro (in SBF) behaviour of hydroxyapatite (HAp) obtained from pork bone sludge from meat plant via two essentially different calcination methods using a stationary, electrically heated chamber oven and enlarged laboratory scale rotary kiln designed by the authors, heated by gas combustion methods enabling application of different set of physical parameters such as temperature, holding time-differing according to type of the kiln. HAp ceramic discs, after 62-days of incubation in SBF at 37 °C, characterized by X-ray diffraction (XRD), FTIR, SEM and EDS methods, underwent changes recorded by:

1. a reduction in Ca/P molar ratio in all the investigated materials resulting from modification in phase composition and

2. weight increase in the investigated disc-samples, resulting from a precipitation of newly formed phase as an admixture of primary HPO$^{2-}_{4}$-free HAp.

They were: secondary (with HPO$^{2-}_{4}$ incorporated) HAp and chlorapatite in all the samples, while in addition to the listed above, 𝛽-tricalcium phosphate was formed on the discs made of HAp from stationary chamber oven, but not from rotary kiln. The new phases were formed in agglomerates on the surface of the investigated ceramic discs and in their pores. The results obtained proved that calcination conditions of pork bone sludge (temperature 750–950 °C, time and type of the applied kiln) under which hydroxyapatite (HAp) powders were obtained had an impact on its different behaviour in SBF, nevertheless, indicating a potential ability of the material to form a new biologically relevant interface with hard tissue and suitability for further investigations intended for medical grafting.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019