• Volume 39, Issue 4

August 2016,   pages  913-1138

• Characterization of microstructure and properties of Al–Al$_3$Zr–Al$_2$O$_3$ composite

Aluminium-based metal matrix composite strengthened by in situ Al$_2$O$_3$ and Al$_3$Zr particles were synthesized by powder metallurgy route. Phase analysis by X-ray diffraction and scanning electronmicroscopy revealed that the reaction between Al and ZrO$_2$ produced Al$_2$O$_3$ and Al$_3$Zr phases in the sintered composites. The hardness of the composite is a strong function of sintering temperature as well as the volume fraction of reinforcements. The dry sliding wear test results clearly indicated that increasing the volume fraction of zirconia particles in the compositeimproved the wear resistance. Microcutting, ploughing, delamination and oxidation were the main mechanisms of wear.

• Synthesis of nanocrystalline TiB$_2$ powder from TiO$_2$, B$_2$O$_3$ and Mg reactants through microwave-assisted self-propagating high-temperature synthesis method

In this research work, microwave-assisted self-propagating high-temperature synthesis (SHS) process was employed for the fabrication of titanium diboride (TiB$_2$) compound from TiO$_2$–B$_2$O$_3$–Mg mixtures. Thermodynamicevaluations of this system and its relevant subsystems revealed that TiB$_2$–MgO composite powder can be easily produced by a SHS reaction. However, experimental results of a TiO$_2$ : B$_2$O$_3$ : 5 Mg mixture heated in a domestic oven showed the formation of some intermediate compounds such as Mg3B2O6, presumably due to some degree of Mg loss. The optimum amount of Mg in TiO$_2$ : B$_2$O$_3$ : xMg mixtures, yielding the highest amount of TiB$_2$ phase, was found to be around 7 mol, i.e., 40 mol% more than the stoichiometric amount. Experimental results revealed thata pure TiB$_2$ compound could be obtained by leaching the unwanted by-products in an HCl acid solution. Scanning electron microscopic observations and Scherrer calculations showed that the produced TiB$_2$ contains sub-micron (150–200 nm) particles, where each particle consists of a number of nanosized (32 nm) crystallites.

• Synthesis of exfoliated PA66 nanocomposites via interfacial polycondensation: effect of layered silicate and silica nanoparticles

Nanocomposites of polyamide 66 (PA66) with layered silicate and silica (SiO2) nanoparticles were prepared via in situ interfacial polycondensation method. Hexamethylenediamine (HDMA) and adipoyl chloride(AdCl) were reacted in a two-phase media. Montmorillonite (NaMMT) and silica nanoparticles were added to reacting media. Preparation of PA66 and its nanocomposites were studied using Fourier transform infrared spectroscopy.Dispersion of nanoparticles was studied using X-ray diffraction and transmission electron microscopy. The results show that two structures were achieved using two kinds of nanoparticles. Silica nanoparticles were partially exfoliated, while NaMMT nanoparticles were hybrid intercalated–exfoliated in nanocomposite samples. Thermal properties of samples were investigated by differential scanning calorimetry. The results suggest that crystallinity is heterogeneous in the presence of nanoparticles. Kinetic of crystallization was studied by means of Avrami equation, based on the kinetic parameters, spherulites are produced. Results were reported for nanocomposites containing 2 and 4% of nanoparticles. Avrami equation parameter, n, shows that spherulite crystallization occured in the samples. Addition of nanoparticles decreases n first, then n increases with nanoparticle content.

• Hydrothermal synthesis, characterization and luminescent properties of lanthanide-doped NaLaF$_4$ nanoparticles

Nanoparticles of sodium lanthanum (III) fluoride-doped and co-doped with Eu$^{3+}/Tb$^{3+}$were prepared by the hydrothermal method using citric acid as structure-directing agent. Structural aspects and optical properties of synthesized nanoparticles were studied by powder X-ray diffraction (XRPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectra (EDS), particle size by dynamic light scattering (DLS), Fourier transform infrared (FTIR) spectrum and photoluminescence (PL) techniques. Nanoparticles consist of well-crystallized hexagonal phase and the average crystallite size for undoped and doped-NaLaF$_4$nanoparticles are in the range of 20–22 nm. TEM images show that nanoparticles have cylindrical shape and crystalline nature of nanoparticles was confirmed by SAED patterns. Downconversion(DC) luminescent properties of doped NaLaF4 were also investigated and impact of co-doping has been explored. • Synthesis and investigation of silicon carbide nanowires by HFCVD method Silicon carbide (SiC) nanowire has been fabricated by hot filament chemical vapour deposition (HFCVD) mechanism in the temperature range of 600–800$^{\circ}$C. Synthesis is performed under vacuum in the atmospheres of hexamethyldisiloxane/alcohol (HMDSO/C2H5OH) vapour and hydrogen (H$_2) gas mixture. In this research dependence of SiC properties on temperature is discussed. Morphology and structural properties of SiC nanowire grown on glass substrate were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy diffraction spectrometer (EDX), and four-point probe (4PP). Also Mountains Map Premium (64-bit version)software is used to investigate morphological features of samples. In this context, the analysis of the motifs, depth histograms, statistical parameters, texture direction, fractal, and the peak count histograms of the nanostructuresurface of samples are carried out. According to analysis, SiC films had a good crystal quality without defects or low residual stress. We found that increasing substrate temperature increases silicon and oxygen doping amount. We also found that electrical resistivity and surface roughness increased by increasing substrate temperature. This study showed that SiC nanowires with high density grew on the free catalyst glass substrate, and the alignment of SiC nanowires decreased. • Erratum to: Synthesis and investigation of silicon carbide nanowires by HFCVD method The original publication of this article had errors, it had to be updated and republished. • Evaluation of electromagnetic shielding effectiveness of multi-axial fabrics and their reinforced PES composites The usage of electrical and electronic equipments has been increasing in daily life, which has a potential hazardous impact on humans and other living organisms. In this paper, multi-axial fabrics containing steel yarns and carbon filaments, and their polyester (PES) resin-reinforced composites have been prepared for electromagnetic shielding applications. The electromagnetic shielding effectiveness (EMSE) of these structures was determined by using coaxial transmission line measurement technique. There were eight different multi-axial fabrics constructed. It was observed that the amount and the orientation of carbon and stainless steel yarns influenced the EMSE performances of multi-axial fabrics and their reinforced PES composites. The structures containing both carbon filaments and stainless steel yarns exhibited better EMSE than the ones including only one type of conductive yarns or filaments. Also, the EMSE performance of multi-axial fabrics was found better than their reinforced composites. The best EMSE results were obtained for the fabric, including two layers of yarns (steel and carbon) on top of each otherin the centre with the angle of 45 and−$45$^{\circ}$. • Assessment of mechanical and three-body abrasive wear peculiarity of TiO$_2$- and ZnO-filled bi-directional E-glass fibre-based polyester composites This paper is about the development of bi-directional E-glass fibre-based polyester composites filled with zinc oxide (ZnO) and titanium dioxide (TiO$_2$) fillers, respectively. The mechanical characterization of these composites is performed. The three-body abrasive wear characteristic of fabricated composites has been assessed under different operating conditions. For this, the three-body abrasion test is done on dry abrasion test rig (TR-50)and analysed using Taguchi’s experimental design scheme and analysis of variance. The results obtained from these experiments are also validated against existing microscopic models of Ratner–Lancaster and Wang. A good linear relationship is obtained between specific wear rate and the reciprocal of ultimate strength and strain at tensile fracture of these composites. It indicates that the experimentally obtained results are in good agreement with theseexisting models. It is found that the tensile strength decreases with filler loading, while hardness, flexural strength, inter-laminar shear strength and impact strength are increased. TiO$_2$-filled composites were observed to performbetter than ZnO-filled composites under abrasive wear situations. The wear mechanism is studied in correlation with the SEM micrograph of the worn-out surface of composites. Performance optimization of composites is doneby using VIKOR method. • Microwave energy-assisted formation of bioactive CaO–MgO–SiO$_2$ternary glass from bio-wastes Regeneration technique is extensively being sought after as a means of achieving bone repair without adverse immunological response. Silicate-based bioactive glasses containing Mg are gaining increasing attention for their biocompatibility. The current work has been focused on designing a facile and economic route using bio-wastes for synthesizing bioactive glasses in the CaO–MgO–SiO$_2$system. Rice husk ash (RHA) obtained from burning ricehusk was used as silica source, while Ca was extracted from eggshells for preparing the glass through a modified sol–gel approach. The gel formed was irradiated in microwave before sintering at 950$^{\circ}$C for 3 h. Thereafter, bioactivity test was conducted on the samples in simulated body fluid (SBF) at physiological conditions for a maximum of 14 days. Characterization of samples were performed before and after immersion in SBF to evaluate thecomposition, morphology and phases present in the glass using energy-dispersive X-ray analysis, scanning electron microscopy and X-ray diffraction. Apatite formation was confirmed using Fourier transform infrared spectroscopy.Results obtained showed the presence of diopside, wollastonite and pseudo-wollastonite as major bioactive phases. Hydroxyapatite formed on the material within 3 days in SBF, indicating good bioactivity. • Kinetics of light-assisted physical ageing in S-rich arsenic sulphide glasses The obtained results show that kinetics of light-assisted physical ageing in S-rich glasses can be well fitted with stretch-exponential Kohlrausch-type function, in which exponent$\beta$-values and the effective time relaxationconstant τ depend on the wavelength of incident photons. The obtained$\beta$-values exhibit well-expressedminimum for the structural relaxation stimulated by light with energy of quanta comparable with the optical gap of the material. This effect is found to be similar to Se-rich glasses. • Spectral studies on CuO in sodium–calcium borophosphate glasses Transparent borophosphate glasses doped with CuO were prepared by melt quenching technique. X-ray diffraction (XRD), optical and luminescence properties of sodium–calcium borophosphate glasses doped with CuO have been studied. The XRD results showed the amorphous nature of the sample. The introduction of CuO was favourable for the colour changes from light blue to dark bluish green colour. Direct optical energy bandgaps before and after doping with different percents of copper oxide obtained in the range 4.81–2.99 eV indicated the role of copper in the glassy matrix by ultraviolet (UV) spectra. The glasses have more than 80% transparency for emission wavelength range, and strong absorption bands due to the charge transition of the Cu$^+$and Cu$^{2+}$ions were observed. The emission bands observed in the UV and blue regions are attributed to 3d$^9$4s–3d$^{10}$triplet transition in Cu$^+$ion. • Selective extraction and detection of noble metal based on ionic liquid immobilized silica gel surface using ICP-OES In this study, an efficiently employed ionic liquid combined with commercially available silica gel (SG–ClPrNTf$_2$) was developed for selective detection of gold(III) by use of inductively coupled plasma–optical emission spectrometry (ICP-OES). The selectivity of SG–ClPrNTf$_2$was evaluated towards seven metal ions, including Y(III), Mn(II), Zr(IV), Pb(II), Mg(II), Pd(II) and Au(III). Based on pH study and distribution coefficient values, the SG–ClPrNTf$_2$phase was found to be the most selective towards Au(III) at pH 2 as compared to other metal ions. The adsorption isotherm of Au(III) on the SG–ClPrNTf$_2$phase followed the Langmuir model with adsorption capacity of 59.48 mg g$^{−1}$, which was highly in agreement with experimental data of adsorption isotherm study. The kinetics study indicated that Au(III) adsorption kinetics data were well fit with the pseudo-second-order kinetic model on the basis of correlation coefficient fitting (0.996) and adsorption capacity agreement (62.26 mg g$^{−1}$). Furthermore, SG–ClPrNTf$_2$phase was effectively performed for the determination of Au(III) in real water samples with satisfactory results. • Electrochemical deposition of Ni–TiN nanocomposite coatings and the effect of sodium dodecyl sulphate surfactant on the coating properties Ni–TiN nanocomposite coatings were prepared by using electrochemical deposition in a Watt’s bath containing TiN particles to increase the hardness of Ni. The effects of deposition current density, electrolyte agitation speed and the number of particles in the solution on the amount of incorporated particles in the coating process were investigated. The optimum deposition current density of 4 A dm$^{−2}$and agitation speed of 450 rpm were obtained. The effect of sodium dodecyl sulphate (SDS) anionic surfactant on the amount of particles in the coatings was investigated. It was observed that the maximum amount of incorporated particles, with a value of 7.5% by volume, was created in the current density of 4 A dm$^{−2}$, stirring rate of 450 rpm, 30 g l$^{−1}$TiN particles and in the presence of 0.6 g l$^{−1}$SDS anionic surfactant. • Cu$^{2+}$and Al$^{3+}$co-substituted cobalt ferrite: structural analysis, morphology and magnetic properties Cu–Al substituted Co ferrite nanopowders, Co$_{1−x}$Cu$_x$Fe$_{2−x}$Al$_x$O$_4$($0.0 ≤ x ≤ 0.8$) were synthesized by the co-precipitation method. The effect of Cu–Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emissionscanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu–Al substitution and its impact on particle size, magnetic properties such as Ms and Hc. Cu–Alsubstitution occurs and produce a secondary phase,$\alpha$-Fe$_2$O$_3$. The crystallite size of the powder calcined at 800$^{\circ}$C was in the range of 19–26 nm. The lattice parameter decreases with increasing Cu–Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 ($v_1$) and 400 cm$^{−1}$($v_2$). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu–Al contents. The saturation magnetization decreases with the increase in Cu–Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction. • Reversible papain immobilization onto poly(AAm–MMA)-based cryogels In the present work, new dye ligand affinity chromatographic support for papain adsorption was synthesized. For this purpose, poly(acrylamide–methyl methacrylate) [poly(AAm–MMA)] cryogels were synthesized by using the free radical cryopolymerization technique. These cryogels were then functionalized with Reactive Green 19 dye and were characterized with Fourier transform infrared, environmental scanning electron microscopy, macroporosityand energy-dispersiveX-ray spectrometer analyses. Incorporation of the dye molecule onto cryogel structure was clearly demonstrated by these characterization techniques and pore diameter of the cryogel was found to bearound 30–40$\mu$m. Effects of medium pH, initial papain concentration, medium temperature and ionic strength on the papain adsorption onto dye-attached cryogel were also investigated. Maximum papain adsorption was found to be 40.66 mg g$^{−1}$cryogel by using pH 5.5 acetate buffer at 25$^{\circ}$C. Reusability profile of the cryogel was also investigatedand it was found that the adsorption capacity of the cryogel decreased only about 2.13% at the end of the 10 reuses. Activity studies of papain in desorption medium were carried out and it was found that desorbed papain wasactive and showed 88.5% of its initial activity. • Preparation and characterization of PAN–KI complexed gel polymer electrolytes for solid-state battery applications The free standing and dimensionally stable gel polymer electrolyte films of polyacrylonitrile (PAN): potassium iodide (KI) of different compositions, using ethylene carbonate as a plasticizer and dimethyl formamide as solvent, are prepared by adopting ‘solution casting technique’ and these films are examined for their conductivities. The structural, miscibility and the chemical rapport between PAN and KI are investigated using X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry methods. The conductivity is enhanced with the increase in KI concentration and temperature. The maximum conductivity at 30$^{\circ}$C is found to be$2.089 \times 10^{−5}$S cm$^{−1}$for PAN:KI (70:30) wt%, which is nine orders greater than that of pure PAN (${\lt}10^{−14}$S cm$^{−1}$). The conductivity-temperature dependence of these polymer electrolyte films obeys Arrhenius behaviour with activation energy ranging from 0.358 to 0.478 eV. The conducting carriers of charge transport in these polymer electrolyte films are identified by Wagner’s polarization technique and it is found that the charge transport is predominantlydue to ions. The better conducting sample is used to fabricate the battery with configuration K/PAN$+$KI/I$_2+$C$+$electrolyte and good discharge characteristics of battery are observed. • Structural and frequency dependencies of a.c. and dielectric characterizations of epitaxial InSb-based heterojunctions In this work, heterojunction of InSb/InP was grown by liquid phase epitaxy (LPE). Surface morphology and crystalline structure of the heterojunction were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The frequency and temperature dependences of a.c. conductivity and dielectric properties of the heterojunctions were investigated in the ranges of 100 kHz–5 MHz and 298–628 K, respectively. The a.c. conductivity and its frequency exponents were interpreted in terms of correlated barrier hopping model (CBH), as the dominant conduction mechanism for charge carrier transport. The calculated activation energy, from the Arrhenius plot, was found to decrease with increasing frequency. Experimental results of both dielectric constant$\epsilon_1$and dielectric loss$\epsilon_2$showed a remarkable dependence of both frequency and temperature. • Luminescence performance of Eu$^{3+}-doped lead-free zinc phosphate glasses for red emission

In this study, the luminescence performance of zinc phosphate glasses containing Eu$^{3+}$ ion with the chemical compositions $(60–x)NH_4H_2PO_4-20ZnO-10BaF_2-10NaF–x$ Eu$_2$O$_3$ (where $x = 0.2, 0.5, 1.0$ and 1.5 mol%) has been studied. These glasses were characterized by several spectroscopic techniques at room temperature. Allthe glasses showed relatively broad fluorescence excitation and luminescence spectra. Luminescence spectra of these glasses exhibit characteristic emission of Eu$^{3+}$ ion with an intense and most prominent red emission (614 nm), which is attributed to ${}^5$D$_0\to {}^{7}$F$_2$ transition. Judd-Ofelt ($\Omega_2$, $\Omega_4$) parameters have been evaluated from the luminescence intensity ratios of ${}^5$D$_0\to {}^{7}$F$_J$ (where $J = 2$ and 4) to ${}^5$D$_0\to {}^{7}$F$_1$ transition. Using J-O parameters and excitationspectra, the radiative parameters are calculated for different Eu$^{3+}-doped glasses. Effect of$\gamma$-irradiation at fixed dose has been studied for all the Eu$^{3+}$-doped glass matrices. The lifetimes of the excited level,${}^{5}D$_0$, have been measured experimentally through decay profiles. The colour chromaticity coordinates are calculated and represented in the chromaticity diagram for Eu$^{3+}$-doped zinc phosphate glasses for all concentrations.

• Reinforcing graphene oxide/cement composite with NH$_2$ functionalizing group

In this study, pure and NH$_2$-functionalized graphene oxide (GO) nanosheets have been added to the cement mortar with different weight percents (0.05, 0.10, 0.15, 0.20 and 0.25 wt%). In addition, the effects of functionalizing GO on the microstructure and mechanical properties (flexural/compressive strengths) of cement composite have been investigated for the first time. Scanning electron microscopy (SEM) images showed that GO filledthe pores and well dispersed in concrete matrix, whereas exceeding GO additive from 0.10 wt% caused the formation of agglomerates and microcracks. In addition, mercury intrusion porosimetry confirmed the significant effects of GO and functionalizing groups on filling the pores. NH2-functionalizing helped to improve the cohesion between GO nanosheets and cement composite. Compressive strengths increased from 39 MPa for the sample without GO to54.23 MPa for the cement composites containing 0.10 wt% of NH$_2$-functionalized GO. Moreover, the flexural strength increased to 23.4 and 38.4% by compositing the cement paste with 0.10 wt% of pure and NH$_2$-functionalized GO, compared to the sample without GO, respectively. It was shown that functionalizing considerably enhanced the mechanical properties of GO/cement composite due to the interfacial strength between calcium silicatehydrates (C-S-H) gel and functionalized GO nanosheets as observed in SEM images. The morphological results were in good agreement with the trend obtained in mechanical properties of GO/cement composites.

• Efficient strategy to Cu/Si catalyst into vertically aligned carbon nanotubes with bamboo shape by CVD technique

Bamboo-shaped vertically aligned carbon nanotubes (bs-VACNTs) were fabricated on Cu/Si catalyst by chemical vapour deposition (CVD) technique under the atmospheric pressure. The catalytic material (Cu/Si) playeda vital role in attaining bs-VACNTs, which is synthesized by drop cast method in a cost-effective manner. Using this catalytic support, we have achieved the tip growth bs-VACNTs at low temperature with well graphitization. The as-grown carbon material was then characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) analyzer, high-resolution transmission electron microscope (HRTEM) and Raman spectroscopy. XRD technique confirms the formation of hexagonal graphitic carbon planes of carbon nanotubes (CNTs). The surface morphology of the material was characterized by SEM, which clearly infervertically aligned CNTs. The nature, diameter and crystallinity were noticed by HRTEM and Raman spectroscopy, respectively. Further, we have also studied the electrochemical properties of the bs-VACNTs and it seems to be proved as highly electroconductive when compared to multi-walled carbon nanotubes (MWCNTs).

• Spin-wave excitations and magnetism of sputtered Fe/Au multilayers

The spin-wave excitations and the magnetism of Fe/Au multilayers with different Fe thicknesses (tFe) grown by RF sputtering were investigated. The temperature dependence of spontaneous magnetization is well described by a T$_{3/2}$ law in all multilayers in the temperature range of 5–300 K. Spin-wave theory has been used to explain the temperature dependence of the spontaneous magnetization and the approximate values for the exchangeinteractions for various $t_{\rm Fe}$ were obtained. The spin-wave constant $B$ was found to increase linearly with the inverse in the Fe thickness ($1/t_{\rm Fe}$). Using the ferromagnetic resonance technique, the change of the anisotropy field $H_K$ as a function of $1/t_{\rm Fe}$ was deduced. The spatial distributions of the discrete spin-wave modes were calculated. All theextracted results were in agreement with those determined experimentally and found in the literature.

• Electrospun chitosan/baker’s yeast nanofibre adsorbent: preparation, characterization and application in heavy metal adsorption

In this study, chitosan/baker’s yeast nanofibre was synthesized by electrospinning method and subsequently, the performance of the prepared nanofibre for removal of uranium(VI) and thorium(IV) ions from aqueous solutions was investigated. The prepared adsorbent was characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. The influences of experimental parameters on the chitosan/baker’s yeast nanofibre such as contact time, pH, temperature and initial concentration were studied in a batch system. The adsorption kinetics was studied by the pseudo-firstorder, pseudo-second-order, double-exponential and intra-particle kinetic models. Three isotherm models, namely Langmuir, Freundlich and Dubinin–Radushkevich (D–R) were used for analysis of equilibrium data of heavymetals. The maximum adsorption capacities of U(VI) and Th(IV) were estimated by Langmuir model to be 219 and 131.9 mg g$^{−1}$ at optimum conditions, respectively. The positive values of the enthalpy changes and negative values of Gibbs free energy changes showed that U(VI) and Th(IV) adsorption process was endothermic and spontaneous. Also, the inhibitory effect of Co(II), Cu(II), Cd(II), Fe(II) and Ni(II) metal ions on U(VI) and Th(IV) adsorption was investigated. The reusability of chitosan/baker’s yeast nanofibre was determined after five adsorption–desorption cycles.

• Effect of increasingly metallized hybrid reinforcement on the wear mechanisms of magnesium nanocomposite

Strength and ductility of pure magnesium have experienced simultaneous improvement due to the presence of nanosize hybrid (yttria and copper) reinforcement. Increasing the vol% (i.e., 0.3–1.0) of ductile metallic copper particles in reinforcement has further enhanced the strength of agnesium.Wear behaviour of these magnesium hybrid nanocomposites was investigated using pin-on-disc dry sliding tests against hardened tool steel using a constant sliding speed of 1ms$^{−1}$ under a range of loads from5 to 30 N for a sliding distance of 1000 m. Scanning electron microscopy identified abrasion and delamination as primary wear mechanisms in the hybrid nanocomposite.Oxidation was active in nanocomposite with higher copper content, tested under higher load and positively affected the wear resistance. Limited thermal softening was observed when tested at a relatively higher load. High frictional heat dissipation capacity couples with higher hardness resisted adhesive wear which is common mechanism for magnesium composite.

• Investigations on structural disorder-induced modifications in the transport behaviour of rare-earth manganites

The results of the studies on structural disorder-induced modifications in the transport behaviour of La$_{0.5}$Pr$_{0.2}$Ca$_{0.3−x}$Ba$_x$MnO$_3$ (LPCBMO) ($0.05 ≤ x ≤ 0.30$) manganites were reported. Structural studies using X-ray diffraction (XRD) measurements confirmed the single phasic nature of all the samples without any detectable impurities. The A-site size disorder ($σ_2$ A) increased from $3.81 \times 10^{−5} (x = 0.05)$ to $14.9 \times 10−5 (x = 0.30)$. With the increase in structural disorder in LPCBMO system, the transport improved for the range: $0.15 ≤ x ≤ 0.30$, which can be ascribed to the enhancement in one electron bandwidth which dominates over the structural disorder effect, while for lower values of $x$, strong competition existed between size disorder and one electron bandwidth. Below 50 K, all $\rho–T$ plots showed resistivity minimum behaviour, which modified with disorder. This behaviour wasdiscussed in detail on the basis of electron–electron interaction having the form: $\rho = [1/(\rho_0 + BT^{1/2})] + \rho_nT_n$. Variation in temperature sensitivity with disorder was also discussed in context of granular morphology and phasesegregation scenario.

• Mechanochemical synthesis and characterization of pure Co$_2$B nanocrystals

Cobalt boride (Co$_2$B) is a significant transition metal boride having a wide range of usage area due to its high oxidation, abrasion and corrosion resistance as well as its superior electrochemical, magnetic and anisotropicproperties. In this study, pure Co2B nanocrystals were synthesized with Co, B$_2$O$_3$ and Mg as starting materials via the mechanochemical synthesis (MCS) method by high-energy planetary ball mill in a hardened steel vial withhardened steel balls. All the experiments were conducted under Ar atmosphere at different rotational speeds and at 20:1–30:1–40:1 ball-to-powder ratios. Leaching of Co$_2$B $+$ MgO powder mixtures occurred after milling andpurified with acetic acid and pure Co$_2$B nanocrystals were obtained in solid form. The Co2Bs were characterized through X-ray diffraction, scanning electronmicroscopy, vibrating samplemagnetometer, Brunauer–Emmett–Tellerand specific density analyses, and effects of synthesis parameters on product properties were revealed. Surface areas of the powders synthesized at 40:1 ball-to-powder ratio at different rotational speeds were measured as 21.14,40.36 and 52.33 m$^2$ g$^{−1}$, respectively. Crystallite sizes of Co$_2$B nanocrystals were between 7.27 and 9.84 nm and their specific density varied between 7.61 and 7.78 g cm$^{−3}$. It was determined that all samples were saturated and exhibited hysteresis and ferromagnetic behaviours, and saturation magnetization was between 35 and 50 emu g$^{−1}$.

• Slow evaporation method and enhancement in photoluminescence properties of YPO$_4$ : Eu$^{3+}$ co-doped with Bi$_{3+}$ ions

The series of Bi$^{3+}$ co-doped YPO$_{4}:Eu$^{3+}$nanophosphors were successfully synthesized by the slow evaporation method. Bi$^{3+}$-doped and un-doped YPO$_4$:Eu$^{3+}$phosphors were characterized by using powder X-ray diffraction, Fourier transform infrared spectroscopy and field emission scanning electron microscopy. Photoluminescence (PL) properties and decay time of phosphors were studied at room temperature. The YPO$_4$:Eu$^{3+}$and Bi$^{3+}$exhibit enhancement in PL intensity and quenched at 0.5 mol% of Bi$^{3+}$ions. • Electric properties of textured (K$_{0.44}$Na$_{0.52}$Li$_{0.04}$)(Nb$_{0.86}Ta$_{0.10}$Sb$_{0.04}$)O$_3$ thick film prepared by screen printing method

Textured (K$_{0.44}$Na$_{0.52}$Li$_{0.04}$) (Nb$_{0.86}$Ta$_{0.10}$Sb$_{0.04}$)O$_3$ thick film was fabricated by the screen printing method with plate-like NaNbO3 particles as template. Thick film with 75% grain orientation was prepared. Remnant polarization and coercive field observed from the P–E loops of textured thick film were 3.6 $\mu$C cm$^{−2}$ and 21 kV cm$^{−1}$, respectively. Textured (K$_{0.44}$Na$_{0.52}$Li$_{0.04}$) (Nb$_{0.86}$Ta$_{0.10}$Sb$_{0.04}$)O$_{3}$ thick film exhibited diffusion behaviour by analysing the temperature dependence of permittivity and loss tangent. The result of leakage current density showed a conduction mechanism of Schottky emission. Piezoelectric (PZT) properties of the thick film were characterized by the relationship of unipolar strain and applied electric field and the PZT constant $d^∗_{33}$ of textured thick film reached to 150 pm V$^{−1}$. Nonlinear PZT property of the thick film was investigated by Rayleigh law.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 5
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019