• Volume 38, Issue 7

December 2015,   pages  1673-1897cq

• Magnetic properties and microwave absorption properties of short carbon fibres coated by Ni–Fe alloy coatings

Ni–Fe alloy coatings were successfully prepared on carbon fibre (CF) surfaces bymeans of electroplating at 25°C for 560 s. The structures and morphologies of the composite were characterized using X-ray diffraction and scanning electron microscopy. The coercivity (𝐻𝑐) and saturation magnetization (𝐻𝑠) of the Fe0.45Ni0.55/CF composites were 45.19 Oe and 1513.59 emu g−1, respectively. The reflectivity of Fe0.45Ni0.55/CF composites was less than −5 dB over the range of 1.1–5.4 GHz. The reflectivity of Fe0.45Ni0.55/CF composites was less than −10 dB over the range of 1.6–2.1 GHz. The lowest reflectivity of the Fe0.45Ni0.55/CF composites was −14.7 dB at 2.0 GHz and the corresponding thickness was 3.3 mm.

• Hot corrosion performance of LVOF sprayed Al2O3–40% TiO2 coating on Superni 601 and Superco 605 superalloys at 800 and 900°C

Al2O3–40% TiO2 coating is deposited on Superni 601 and Superco 605 superalloys by low-velocity oxy-fuel (LVOF) process. LVOF sprayed coating is characterized for surface roughness, microhardness, scanning electron microscopy and X-ray diffraction analysis. Hot corrosion of the coated and uncoated superalloys have been evaluated in an aggressive environment of Na2SO4–82% Fe2(SO4)3 under cyclic conditions at temperatures of 800 and 900°C. The microhardness and surface roughness values of the as-sprayed coatings are found to be in the range of 742–946 Hv and 14.40–14.80 𝜇m, respectively. Al2O3–40% TiO2 coating on both the superalloys has indicated protective behaviour during hot corrosion studies.

• Influence of silicon addition on the mechanical properties and corrosion resistance of low-alloy steel

The addition of silicon to low-alloy steel allows to modify the materials' microstructure and thus to improve their corrosion resistance and mechanical properties. The influence of adding different amounts of silicon on the properties (density, transverse rupture strength, microhardness and corrosion resistance) and microstructure of low-alloy steel was investigated. Samples were prepared via the mechanical alloying process, which is the most useful method to homogeneously introduce silicon to low-alloy steel. Sintering was performed by using the spark plasma sintering (SPS) technique. After the SPS process, half of each of the obtained samples was heat-treated in a vacuum furnace. The results show that high-density materials were achieved, and a homogeneous and fine microstructure was obtained. The investigated compositions containing 1 wt% of silicon had better corrosion resistance than samples with 3 wt% of silicon addition. Furthermore, corrosion resistance as well as the mechanical and plastic properties of the samples with 1 wt% of silicon can be further improved by applying heat treatment.

• A thermodynamic approach towards glass-forming ability of amorphous metallic alloys

A quantitative measure of the stability of a glass as compared to its corresponding crystalline state can be obtained by calculating the thermodynamic parameters, such as the Gibbs free energy difference (𝛥𝐺), entropy difference (𝛥𝑆) and the enthalpy difference (𝛥𝐻) between the super-cooled liquid and the corresponding crystalline phase. 𝛥𝐺 is known as the driving force of crystallization. The driving force of crystallization (𝛥𝐺) provides very important information about the glass-forming ability (GFA) of metallic glasses (MGs). Lesser the driving force of crystallization more is the GFA. The 𝛥𝐺 varies linearly with the critical size (𝑑𝑐). According to Battezzati and Garonne the parameter 𝛾 ( = (1−(𝛥𝐻𝑥/𝛥𝐻𝑚))/(1−(𝑇 𝑥/𝑇 𝑚))) in the expression for 𝛥𝐺 should be a constant (i.e., 0.8), but its uniqueness is not observed for all MGs. The thermal stability of various alloy compositions is studied by their undercooled liquid region (𝛥𝑇 = 𝑇 𝑥 − 𝑇 𝑔). Large 𝛥𝑇 𝑥 implies greater stability against crystallization of the amorphous structure. Other GFA parameters are also calculated and correlated with critical size (𝑑𝑐).

• Investigation of the effects of temperature and time on reduction of graphene oxide by microwave hydrothermal reactor

Graphene oxide (GO) sheets were synthesized by modified Hummers method. Microwave hydrothermal reactor (MHR) was applied to reduce graphene oxide. Different temperatures 50 and 180°C were applied to fabricate four samples with 4, 10, 25 and 60 min exposure times. The deoxygenation of the GO sheets after exposure to MHR was revealed by using UV–visible, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and Raman spectroscopy. Based on XPS analysis, the O/C ratio of the GO sheets decreased from 49 to 17% after exposure to MHR. On the other hand, characterization by TGA illustrated that the O/C ratio of the GO dramatically decreases after exposure ofMHR and reached from 37 to 7%. Raman spectroscopy demonstrated that there was no increase in defects' density after reduction. The results confirmed that sample with 180°C exposure temperature and 60 min exposure time was reduced completely. Therefore this can help to advance using MHR as the green technique of GO reduction.

• Understanding the impact of graphene sheet tailoring on the conductance of GNRFETs

The effect of tailoring the graphene sheets used as channel in a graphene nanoribbon field effect transistor (GNRFET) was investigated. The study was performed using self-consistent solution of Poisson's and Schrodinger's equation in combination with non-equilibrium Green's function (NEGF) formalism. Graphene sheet channel was tailored into different shapes and found that with the introduction of edge roughness along the border of GNR sheet the bandgap of GNRFET channel increases. Tailoring the channel decreases mobility and transmission probability to a great extent and thus the performance of I–V characteristics of GNRFET degrades.

• Glassy carbon electrodes modified with gelatin functionalized reduced graphene oxide nanosheet for determination of gallic acid

A simple approach for the preparation of gelatin functionalized reduced graphene oxide nanosheet (Gel-RGONS) by chemical reduction of graphene oxide (GO) using gelatin as both reducing agent and stabilizing agent in an aqueous solution was developed. The morphology and structure of the Gel-RGONS were examined by X-ray diffraction, transmission electron microscopy, ultraviolet–visible spectroscopy and Raman spectroscopy. Gelatin acted as a functionalizing reagent to guarantee good dispersibility and stability of the r in distilled water. Moreover, a new electrochemical sensor was developed based on Gel-RGONS modified glassy carbon electrode (Gel-RGONS/GCE). Gel-r exhibits excellent electrocatalytic activity to gallic acid (GA) oxidation. The experimental conditions such as pH, adsorption time and scan rate were optimized for the determination of GA. Under optimum conditions, the sensor responded linearly to GA in the concentration of 1.0 × 10−6 to 1.1 × 10−4 M with detection limit of 4.7 × 10−7 M at 3𝜎 using linear sweep voltammetry (LSV). The method has been successfully applied to the determination of GA in sample of black tea.

• Modified structure of graphene oxide by investigation of structure evolution

The structure of graphite oxide and graphene oxide (GO) has been studied previously using various analyses and computer simulations. Although some oxygen functional groups (OFGs) are accepted as the main functionalities in GO, the structure of GO has remained elusive. In this regard, GO was produced using the modified Hummers method and was investigated using X-ray diffraction pattern, Fourier transform infrared analysis and Boehm titration method. Based on the obtained results, a modified model was proposed for GO based on the model of Lerf-Klinowski. OFGs include highly carboxyl groups and phenols with few epoxides, lactones and ketones agglomerated in some regions due to hydrogen bonding between functional groups. Trapped water molecules were shown between the GO sheets which strongly affected the distribution of OFGs and their aggregation by hydrogen bonding.

• Facet-dependent study of efficient growth of graphene on copper by ethanol-CVD

The growth of graphene by chemical vapour deposition (CVD) on copper is the most promising scalable method for high-quality graphene. The use of ethanol, an economic and safe precursor, for the fast growth of graphene on copper by a home-built CVD set-up was analysed. Full coverage of uniform single-layer graphene with high crystalline quality was found on $\langle100\rangle$ textured Cu foils in just 30 s. The nucleation density of graphene islands was found to be independent of facets but the island shape showed facet dependence. Diamond-like islands were observed on Cu(100) facets while random shaped islands were seen on other facets. The last observation is discussed in terms of a competition between graphene-island growth and its relaxation rate on different facets. On Cu(100) slower island growth as compared to its relaxation leads to equilibrium shapes as opposed to other facets. Further, an observed evolution in graphene contrast in electron micrographs with time on different facets was discussed in terms of oxygen diffusion between graphene and Cu.

• Sintered gahnite–cordierite glass-ceramic based on raw materials with different fluorine sources

Glass-ceramic based on Zn-containing cordierite was prepared from kaolin, silica'sand and commercial ZnO. The addition of AlF3, MgF2 and CaF2 was performed as nucleation catalysts. Dark brown glasses were obtained from the glass batches. The transformation and crystallization temperatures were in the range of 739–773 and 972–1007°C, respectively. Gahnite, cordierite and very little enstatite were the development crystalline phases through the heating and sintering process between 1000 and 1340°C. The microstructure of crystallized samples at 1340°C showed the appearance of dominant euhedral octahedral crystals of gahnite and hexagonal cordierite, in the low micro-scale, disseminated in the glassy matrix. The microanalysis of the crystallized samples indicated that Zn and Mg may replace each other in gahnite and cordierite structure. Densities of the crystallized samples were between 2.2517 and 2.5278 g cm−3. The thermal expansion of the crystallized samples was ranging from 19.22 to 59.30 × 10−7°C−1. However, the higher crystallization of both cordierite and gahnite accompany with the higher values of densities and the lower values of coefficient of thermal expansion.

• Correlation between temperature-dependent permittivity dispersion and depolarization behaviours in Zr4+-modified BiFeO3–BaTiO3 piezoelectric ceramics

The correlation between permittivity frequency dispersion and depoling process upon heating was investigated in Zr4+-modified 0.75BiFeO3–0.25BaTiO3 (BF–BZT) ceramics. The temperature-dependent permittivity 𝜀r(𝑇) and the piezoelectric coefficient 𝑑33 for poled samples were measured under heating conditions to clarify the depolarization mechanism. The results indicate that the poling temperature plays a crucial role in the domains' alignment process, as expected. The temperature-dependent permittivity frequency dispersion and depolarization behaviours may have same origin. The aligned domains' break up into random state/nanodomains at depoling temperature (𝑇 d), which causes strong frequency dependence of the permittivity, simultaneously, induces the loss of piezoelectricity. It suggests that the temperature-dependent permittivity measurements method is a simple way to determine the depolarization temperature.

• Ionic drift velocity measurement on hot-pressed Ag+ ion conducting glass-polymer electrolytes

Ionic drift velocity (𝑣d) measurements of a new Ag+ ion conducting glass-polymer electrolytes (GPEs): (1−x) PEO : x[0.8(0.75AgI:0.25AgCl) : 0.2(Ag2 O:V2O5)], where 0 &lt; x &lt; 50 wt%, were reported. GPEs were casted using the hot-press techniques developed in recent times. The composition: 70PEO : 30[0.8(0.75AgI : 0.25AgCl) : 0.2(Ag2O : V2O5)] with conductivity (𝜎)∼ 7.7 × 10−7 S cm−1 was identified as highest conducting composition from the compositional-dependent conductivity studies. The ionic mobility (𝜇), mobile ion concentration (𝑛), ionic transference number (𝑡ion) and ionic drift velocity (𝑣d) of GPEs were determined at different temperatures with the help of the d.c. polarization technique and other well-known important relations.

• Structural, morphological and magnetic properties of La1−𝑥Na𝑦MnO3 (𝑦 ≤ 𝑥) nanoparticles produced by the solution combustion method

The rapid solution combustion synthesis and characterization of sodium (Na)-substituted LaMnO3 phases at relatively low temperature using polyvinyl alcohol (PVA) as fuel were reported. The thermal decomposition process investigated by means of differential and thermal gravimetric analysis (TG–DTA) showed that the use of PVA as a fuel was satisfactory in the synthesis of the perovskite manganite compound. Structural study using X-ray diffraction showed that all the samples were single phasic without any detectable impurities within the measurement range. Also, the Na-substituted compounds crystallize with rhombohedral symmetry (space group R-3c, no. 167) with La0.80Na0.15MnO3 manganite sample giving the highest crystallinity. Microstructural features observed by field-emission scanning electron microscopy demonstrated that most of the grains were nearly spherical in shape with fairly uniform distribution and all the observed particles connect with each other. Energy-dispersive X-ray analyses confirm the homogeneity of the samples. Increase in magnetic moment was observed with the increase in sodium doping. Room-temperature vibrating sample magnetometer measurements showed that the samples were ferromagnetic with compositions 𝑦=0.10, 0.15 and 0.20 showing relatively high magnetic moments of 33, 34 and 36 emu 𝑔−1, respectively.

• Synthesis of MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres for the removal of Congo Red from aqueous solution

MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres were prepared by urea-hydrolysed hydrothermal reaction and the subsequent calcinations. The morphology and structure of the products were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscope and Fourier transformed infrared. The adsorption performance of MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres for the removal of an anionic dye (Congo Red, CR) from aqueous solution was investigated. The results showed that MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres are particularly efficient in removing CR. The adsorption follows a pseudo-second-order kinetic model and best fits the Langmuir isotherm model. The maximum adsorption capacities of MgAl-LDH/CoFe2O4 and MgAl-CLDH/CoFe2O4 nanofibres for CR were found to be 213.2 and 49.8 mg g−1, respectively. The both adsorption processes were found to be spontaneous and exothermic in nature.

• Lattice dynamical properties of MnTe, HgTe and their mixed semiconductor Mn𝑥Hg1−𝑥Te

In the present paper, the phonon dispersion relations, phonon density of states and Debye characteristics of mixed semiconductor Mn𝑥Hg1−𝑥Te and the end members MnTe and HgTe using three-body shell model were studied. The model involves 11 disposable parameters and incorporates the effect of the short-range repulsive interactions up to and including the second nearest neighbours, in addition to the long-range Coulombic interactions in the framework of the rigid-shell model with both the ions polarizable. The comparisons of the theoretical results with the available experimental results were in good agreement.

• Radiation damage to multi-walled carbon nanotubes and their Raman vibrational modes

Since their discovery in 1991 by Iijima, carbon nanotubes (CNTs) have been of great interest, both from a fundamental point of view and for future applications. As recent experimental and theoretical studies demonstrate, irradiation of CNTs with energetic particles can successfully be used for nano-engineering, e.g., for creating molecular junctions between the nanotubes, making nanotube-based quantum dots and composite materials with enhanced mechanical properties. In this work, the Raman spectroscopy investigation of nanotube defects created by irradiation of Ar+ ions with various energies and doses was presented. In order to obtain more informative data, scanning electron microscope and thermal gravimetric analysis were carried out. Sheet resistivity of samples was also measured with the standard four-point probe technique. From the results, it was evident that the intensity ratio of the D band' at around 1300 cm−1 to the intensity of the G band' at 1590 cm−1, relative intensity of the D to G bands increases with enhancement of the irradiation dose. Comparing the intensity ratio 𝐼 D'/𝐼 G (the D' band was assigned to the lattice defects which occur inside the graphene atomic layer and induces a break in the two-dimensional translational symmetry) with 𝐼 D/𝐼 G tend to decide the D' band treated as a defect. Electrical measurements showed that resistance of samples increases with enhancement of irradiation dose, clearly due to creation of more defects.

• Role of the vacuum pressure and temperature in the shape of metal Zn nanoparticles

Zinc (Zn) nanoparticles were fabricated by the high-vacuum thermal evapouration technique. The vacuum pressure was modified from 10−6 to 15 Torr and the substrate temperature was increased from room temperature to 100°C in order to evaluate the changes in the morphological and structural characteristics of the Zn nanoparticles. Well-faceted hexagonal disk shaped nanoparticles were formed at a vacuum pressure of 10−6 Torr with the substrate kept at room temperature. Aggregation and surface irregularities at the edges of the hexagonal nanodisks were observed with further increases in the vacuum pressure. The nanoscale characteristics of the nanodisks were lost at a vacuum pressure of 10−6 Torr and heating the substrate at 100°C. The nanodisks were transformed into Zn wires at a vacuum pressure of 15 Torr with a substrate temperature of 100°C. It is suggested that the initial stages of the growth of the Zn wires are governed by the agglomeration of the Zn nanodisks since the structure of the wires was observed to be composed by stacked nanodisks.

• Interaction of pristine hydrotalcite-like layered double hydroxides with CO2: a thermogravimetric study

Metal oxides in general have surface acidic sites, but for exceptional circumstances, are not expected to mineralize CO2. Given their intrinsic basicity and an expandable interlayer gallery, the hydrotalcite-like layered double hydroxides (LDHs) are expected to be superior candidate materials for CO2 mineralization. However, the incorporation of Al3+ adversely impacts the ability of the metal hydroxide layer to interact with CO2 in the gas phase in comparison with the unitary Mg(OH)2. Thermogravimetric analysis shows that the decomposition reaction of the [Mg–Al–CO3] LDH is only marginally delayed in flowing CO2 in comparison with flowing N2, showing only an apparent marginal CO2 uptake. Al3+ ion severely attenuates the surface basicity of the LDHs, as the unitary Al(OH)3 is acidic in comparison with Mg(OH)2 and shows little or no interaction with CO2 in the gas phase.

• Optical analysis for few TMDC materials

The transition metal dichalcogenides possess layered structure of Se-M-Se (M = Nb, Mo, Ta and W) sandwich interact with each other by van der Waal forces and can also provide sites for intercalation. Because of their technological importance, lubricants, catalysts, battery cathodes and electrodes in the photoelectrochemical solar cells, much attention has gone in the studies of growth of these materials in crystalline and nanocrystalline forms. In the present work we report the growth of NbSe2, MoSe2, TaSe2 and WSe2 single crystals and determine the optical bandgap using optical absorption. The optical absorption of as-grown crystals has been measured at room temperature near the fundamental absorption edge. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The direct and indirect energy gaps and phonon energies for all crystals have been estimated. The results obtained are discussed in detail.

• Dynamic response of multiwall boron nitride nanotubes subjected to impact

Dynamic behaviours of multiwall boron nitride nanotubes (MWBNNTs) with finite length were studied by employing continuum structure. Multiple elastic shells with nonlinear model of van der Waals interactions were used for developing an inclusive and inexpensive dynamical model of MWBNNTs. The systems of coupled partial differential equations were solved by applying the finite element method. Whole or part of thin and bulky MWBNNTs were exposed to external pressure impact and dynamical treatment were investigated and precision of results were checked by evaluating the answers with those found by other methods. Both deflection and stress studies were carried out for tubes of MWBNNTs and the influences of longitudinal wave caused by external pressure impact were considered in MWBNNTs. Also, time history diagrams of MWBNNTs with impact of initial longitudinal deflection were investigated and the extension of the longitudinal waves through the length of layers were shown and so, wave speed was determined.

• Changes in hydroxyapatite powder properties via heat treatment

The properties of hydroxyaptite (HA) powder, especially its physical one, are largely influenced by the heat treatment process. Controlling of these changes is vital in deciding the suitability of applying this powder in wet processing routes for green body fabrication. Chemically, the crystallinity of the HA powder was found to be largely enhanced with the increase in calcination temperatures. In contrary, a high retardation in the carbonate ion content was found. Physically, all the powder properties in terms of particle size, its distribution, pore volume, pore size and surface area are considerably varied with calcination temperatures. It was found that HA powder calcined at both 1000 and 1100°C possesses reasonable physico-chemical properties for being applied in wet processing routes. Using heat-treated powder at 1000 and 1100°C with 0.3 wt% sodium polyacrylate (as a dispersing agent) turned out to be beneficial in developing a low viscosity and high turbidity suspensions.

• Synthesis of Cu-Al-Zn-O nanocomposite: effect of annealing on the physical properties

We prepared Cu-Al-Zn-O (CAZO) nanocomposite thin films on quartz substrates by radio frequency (RF) magnetron sputtering method. The as-deposited CAZO film is amorphous in nature and annealing in air environment results in weak crystallization of the films and formation of CuAlO2 and CAZO. The surface morphology of the films was studied with atomic force microscopy images, while Rutherford backscattering spectrometry (RBS) was used to characterize material properties. The optical bandgap of films was found to be 3–4.2 eV depending on the annealing temperature. The photoluminescence (PL) of the samples was measured at room temperature. Violet, blue and green spectra peaks were observed from the PL spectra of the four samples. The emission spectrum indicates the suitability of CAZO nanocomposite for gas sensor applications and technology.

• Role of boron addition on the consolidation and properties of steel composites prepared by SPS

Composites reinforced with 8 vol% TiB2 were subjected to the consolidation process by spark plasma sintering (SPS). The results show that the addition of boron (1 vol%) introduced to the steel matrix has a significant effect on the composite microstructure, as well as physical, mechanical and tribological properties. The full density of 97–99% was obtained in the composites sintered at a temperature of 1100°C. The steel–8% TiB2–1% B composite sintered at 1100°C for 30 min was characterized by the highest microhardness (465 HV0.3) and Young's modulus (229 GPa), combined with the best compressive strength (1150 MPa) and abrasive wear resistance (𝜇 = 0.25 and 𝑊 𝑣(disc) = 207.78 × 10−6 mm3 N−1m−1). The microstructure and chemical composition were examined by scanning electron microscopy and transmission electron microscopy. The examinations have revealed the presence of numerous fine complex borides in the microstructure of the steel–8% TiB2 and steel–8% TiB2–1% B composites.

• Synthesis of Co9S8 and CoS nanocrystallites using Co(II) thiosemicarbazone complexes as single-source precursors

Cubic Co9S8 and hexagonal CoS nanocrystallites were prepared by pyrolysis and solvothermal decomposition methods using Co(LH)2Cl2 and CoL2 (where LH = thiosemicarbazones of furfuraldehyde, cinnamaldehyde and 4-fluoro-acetophenone) as single-source precursors. These nanocrystallites were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), selected area electron diffraction, UV–Vis, PL and Raman spectroscopic techniques. From TEM images, the average grain size of asprepared cobalt sulphide nanocrystallites was found to be 7–10 nm. Depending on experimental conditions, various morphologies such as spherical, pyramidal, hollow spheres, etc. are observed in the TEM images.

• Synthesis and optical study of heat-treated ZnO nanopowder for optoelectronic applications

UV emitting ZnO nanopowder was chemically synthesized and subsequently subjected to heat treatment in oxygen atmosphere for potential optoelectronic properties. Characterization including Raman spectroscopy, photoluminescence, SEM, FT-IR and XRD were performed to see the effect of high temperature heat treatment and subsequently oxygen defects on the physical properties of ZnO powder. Chemically prepared product was highly pure polycrystalline w-ZnO with random crystallites orientation. Study showed a magnificent absorption of oxygen by the product as manifested by the decreased intensity of deep-level green emission and E1 (LO) phonon mode. The phonon modes appeared at 276 and 970 cm−1 and which have been assigned to ZnO by the previous researchers under relaxed Raman selection rule were no longer found with heat treatment. UV emission was enhanced and the ratio of UV to green emission (𝐼UV/𝐼 green) was correlated with the crystal structure and oxygen vacancies before and after heat treatment. FT-IR study established strong Zn-O bending and stretching bands at 356 and 498 cm−1. SEM analysis demonstrated fine crystallites distribution in ZnO nanopowder with almost spherical morphologies. Reasonably, a more spherical and ordered morphologies with large grains were found with heat treatment. The investigated findings manifested improved structural and optical properties for various optoelectronic and biomedical applications of technological importance.

• Poly(furfuryl alcohol) nanospheres: a facile synthesis approach based on confinement effect of polymer and a template for synthesis of metal oxide hollow nanospheres

This paper describes a facile hydrothermal approach to the large-scale synthesis of well-dispersed poly(furfuryl alcohol) (PFA) nanospheres with an average diameter of 350 nm in the presence of poly(vinyl pyrrolidone) (PVP). Scanning electron microscopy and transmission electron microscopy studies showed that different morphologies of PFA could be obtained by adjusting the ratio of PVP and furfuryl alcohol (FA). As a whole, the results demonstrate that PVP plays a key role in controlling the polymerization process of FA. The confinement effect of PVP is proposed to explain the formation process of PFA nanospheres. Furthermore, the as-prepared PFA nanospheres have a functional surface that allow them to act as an ideal template for fabricating metal oxide hollow nanospheres.

• Luminescent properties of red-light-emitting phosphors CaWO4 : Eu3+, Li+ for near UV LED

A series of red phosphors Ca1−2𝑥WO4 : 𝑥Eu3+, 𝑥Li+ (𝑥 = 0.01, 0.02, 0.04, 0.06, 0.12, 0.20 and 0.30) in pure phase were synthesized via high-temperature solid-state reaction and their luminescent properties were investigated. For comparison, the 6 mol% Eu3+-doped CaWO4 was also obtained and investigated. The crystal structures of these phosphors were characterized by powder X-ray diffraction, and the luminescent properties of Eu3+-, Li+-codoped CaWO4 were investigated by diffuse reflectance spectra, photoluminescence emission spectra, photoluminescence excitation spectra, and the Commission International de L' Eclairage (CIE) chromaticity indexes. These spectra illustrated that Eu3+-, Li+-codoped CaWO4 phosphors could effectively be excited by a 270 nm ultraviolet (UV) or 394 nm near UV chip, and exhibit red emission originated from the 5D0 $\rightarrow$ 7F𝐽 (𝐽 = 1 and 2) transitions of Eu3+. The fluorescent intensities of red emission band centred at 610 nm of 6 mol% Eu3+-, Li+-codoped CaWO4 were about 1.27 times stronger than that of 6 mol% Eu3+-doped CaWO4 under 394 nm excitation. The 12 mol% doping concentration of Eu3+ ions in CaWO4 is optimum when excited at 394 nm, while excited at 270 nm the sample with 6 mol% was the best one. The concentration quenching mechanism could be attributed to the dipole–dipole interaction between the Eu3+ ions. The CIE colour coordinates can be tuned from yellowish red to deep red with varying concentrations of Eu3+. The present work suggests that Eu3+-, Li+-codoped CaWO4 as red phosphors exhibit great potential application in the near UV excited white-light-emitting diode.

• Co-precipitation synthesis and upconversion luminescence properties of ZrO2:Yb3+-Ho3+

ZrO2:Yb3+-Ho3+ phosphors with different Yb3+ doping concentration have been prepared by coprecipitation method. X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectra were used to characterize the properties of ZrO2:Yb3+-Ho3+ phosphors. Different phases of ZrO2 can be obtained by changing the concentration of Yb3+. Under the 980 nm excitation, the sample gives a set of light: strong green (539 nm), weak red (670 nm) and near-infrared (760 nm). The upconversion luminescence is based on two-photon absorption by the energy transfer from the donor (Yb3+) to the acceptor (Ho3+). All the results indicate that ZrO2:Yb3+-Ho3+ phosphors could be a promising biological labelling material.

• Study of dielectric and ferroelectric properties of five-layer Aurivillius oxides: A2Bi4Ti5O18 (A = Ba, Pb and Sr) synthesized by solution combustion route

This paper presents the ferroelectric and dielectric properties of five-layer Aurivillius oxides (Ba2Bi4Ti5O18, Pb2Bi4Ti5O18 and Sr2Bi4Ti5O18) prepared by a solution combustion route with glycine as a fuel at low calcination temperature. The phase formation of these materials with pseudo-tetragonal structure was achieved after calcination at 750°C for 3 h; as confirmed by X-ray diffraction studies. Scanning electron microscopy of the sintered ceramics shows that the grains exhibit a plate-like morphology. The ferroelectric to paraelectric transition temperature (𝑇𝑐) for Ba-, Pb- and Sr-based bismuth titanate ceramics was found to be 350, 280 and 260°C, respectively. All three materials show multiple relaxation phenomena and their electrical conductivity was found to be temperature dependent. The Pb2Bi4Ti5O18 ceramic possessed the highest value of activation energy (0.68 eV) and hence shows better ferroelectric properties, as compared to barium and strontium bismuth titanates.

• Low resistivity molybdenum thin film towards the back contact of dye-sensitized solar cell

This paper reports the optimization of the molybdenum thin film electrode as the back contact of dye-sensitized solar cell (DSSC). The molybdenum thin film was grown on the glass substrate by direct current sputtering techniques of which the sputtering power was 150Wat 18 sccm flow rate of Ar. At such sputtering parameters, the Mo film can reach the lowest resistivity of 1.28E−6𝛺 cm at 400 nm thick. And the reflection of Mo membrane was 82%. This value is considered as a very good result for preparation of the back contact of DSSC.

• Contents - December 2015

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• Author Index

• Volume Contents

• # Bulletin of Materials Science

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019