• Volume 41, Issue 1

February 2018

• First-principle-based computational doping of SrTiO$_3$ using combinatorial genetic algorithms

Developing new materials has historically been time-consuming. One commonly used approach is materialdoping, in which given a base material, one can change its properties by substituting some elements with new ones or addingadditional elements. Computational material discovery involves searching in a large design space to identify candidates forexperimental verification. Recently, it was possible to obtain many electrical and physical properties of materials by densityfunctional theory based first-principle calculation, making it suitable for computational doping-based material discovery. Incomputational doping, one can substitute some of the atoms in a supercell with dopant atoms. However, the actual positionsof the dopant elements within the supercell are not known. In this work, we developed a genetic algorithm for finding themost stable structure of the doped material with the lowest free electronic energy. For each candidate atom configuration,we use the Vienna Ab-Initio Simulation Package to calculate its physicochemical properties, which takes about 15–30 h fora supercell grid of 75 atoms.We did computational doping on SrTiO$_3$ perovskite. Experiments showed that our method canreduce the running time for computational doping by up to 70% compared with exhaustive sampling as commonly usednow.

• Gd impurities effect on Co$_2$CrSi alloy: first-principle calculations

First-principle calculations have been performed to study Gd impurities doping effect on the physical propertiesof the Heusler half-metallic ferromagnet Co$_2$CrSi using the density functional theory in the local spin density approximationwith an additional Hubbard correlation term for the rare-earth 4f states. The results show that the gadolinium moment isaligned antiparallel to that of transition metal atoms for both Co$_{16}$Cr$_7$GdSi$_8$ and Co$_{15}GdCr$_8$Si$_8$. The analysis of the doped material band structures shows that the half-metallic properties are completely conserved if Gd substitutes Cr atoms, while the minority-spin gap is filled and half-metallicity is lost when Gd substitutes Co atoms. • Embedding of inkjet-printed Ag-grid/ITO hybrid transparent electrode into a plastic substrate for flexible electronic devices Flexible ITO/Ag-grid hybrid layers were prepared by a solution process and embedded into a plastic layer.The structural analysis confirmed that the printed layers were successfully embedded into the plastic substrate without anystructural damage. The detachment of the printed ITO/Ag-grid layers from the glass substrate was carried out by dissolving ametallic sacrificial layer, which deposited on the glass substrate before the printing step. The optimum electrical and opticalperformance was obtained with Ag-grid pitch of 300$\mu$m, leading to the sheet resistance of 2$\Omega$per sq and the transmittance of 85%. • Adsorption property of volatile molecules on ZnO nanowires: computational and experimental approach ZnO nanowires (NWs) were deposited on a glass substrate by the successive ionic layer adsorption and reactionmethod (SILAR). Sensing response of ZnO NWs towards reducing vapours was tested at ambient temperature ($\sim$32$^{\circ}$C)by the chemiresistor method. The vapour response was found to be 80.2, 1.6, 1.1 and 1.1 for NH$_3$,H$_2$O, (CH$_3$)$_2$CO and C$_2$H$_5$OH, respectively. Also, density functional theory (DFT) calculations were performed to understand the charge transfer and electronic property change during adsorption of molecules over ZnO NW. The band of the Zn 3d state was altered after adsorption and no significant changes were observed in the O2p state.Higher binding energy (14.6 eV) with significant chargetransfer (0.04$|e|$) was observed in the ammonia-adsorbed ZnO NW. On comparing response obtained through experimentaland computational studies, almost a similar trend of response was observed except for the H$_2$O–ZnO system. This was dueto lack of dispersion interaction and steric effect influence in the DFT calculation with the chosen computational methods. • Improvement in light-extraction efficiency of light emitting diode using microlenses fabricated by a novel and cost-effective method A low cost, solution-based novel process was proposed, which avoids any photo-lithographically fabricated Si template and yet yields small dimension microlenses. The microlenses were fabricated using a well-known chemical technique called dewetting of polymer thin film. Polystyrene (PS) was used to make a polymer thin film with thickness ranging from 20 to 40 nm. Then, this PS film was kept in dewetting solution namely methylethylketone (MEK) to obtain the microlenses. Dimension of these microlenses was measured to be the order of 1–2$\mu$m. The effect of various microlens parameters such as diameter and area fraction on light-extraction efficiency was systematically studied. Improvement of 4% in extraction efficiency was obtained by employing it on white light emitting diode. The area fraction of microlenses was increased up to 0.34 by reducing the spin speed. The light-extraction efficiency was further enhanced up to 7% uponincreasing the area fraction of microlenses. • Lead ions removal from aqueous solution using modified carbon nanotubes Surface-modified carbon nanotubes (CNTs) were prepared in order to remove lead ions (Pb$^{2+}$) from aqueoussolution. The modification of CNTs was conducted by oxidation, using a mixture of nitric acid (HNO$_3$) and sulphuric acid(H$_2$SO$_4$). The adsorption behaviour was well fitted to the Langmuir model and the maximum adsorption capacity of Pb$^{2+}$was found to be 100 mg g$^{−1}$. The adsorption of Pb$^{2+}$reached equilibrium in 80 min. The experimental data were well fitted to a pseudo-second-order rate model rather than a pseudo-first-order model. The activation energy and activation enthalpy of the adsorption calculated from Arrhenius and Eyring equations were, respectively, 21.08 and 18.56 kJ mol$^{−1}$, which reflect the outside surface adsorption and ion exchange mechanism. The thermodynamical studies showed that the adsorption of Pb$^{2+}$was a spontaneous and endothermic process. The ion exchange mechanism of Pb$^{2+}$removal was confirmed by the pH and electrical conductivity data in solution before and after adsorption. • Synthesis of Co$_3$O$_4$nanocubes by hydrothermal route and their photocatalytic property Monodispersed Co$_3$O$_4$nanocubes were prepared by a simple hydrothermal route with sodium pentanesulphonate,employing Co(NO$_3$)$_2$·6H$_2$O and NH$_3$·H$_2$O (28 wt%) as the starting reactants.The final product was characterizedby powder X-ray diffraction, energy-dispersive X-ray spectrometry, scanning electron microscopy and transmission electronmicroscopy. The as-prepared Co3O4 nanocubes could photocatalytically degrade organic dye Rhodamine B under irradiation of 365 nm ultraviolet light. • A single crystal neutron diffraction study on mixed crystal (K)$_{0.25}(NH$_4$)$_{0.75}H$_2$PO$_4$: tuning of short strong hydrogen bonds by ionic interactions One of the most intriguing facts about hydrogen bonds is that bonds formed between the same couple of donorand acceptor atoms can have large variation in the geometry as well as energies; this is mainly because hydrogen bonds arehighly sensitive to their environment.We report here a comparative study of neutron structures of mixed crystals of potassium–ammonium dihydrogen phosphate. Basic structural framework of crystals belonging to potassium dihydrogen phosphatefamily is constructed by a network of zigzag O–H–O hydrogen bonded chains of PO$_2$(OH)$_2$anions, with cations occupying the interspaces of the zigzagged anionic chains. These crystals having simple crystal structure primarily determined by theO–H–O hydrogen bonds connecting PO$_2$(OH)$_2$anions provide us with a unique opportunity to tune the hydrogen bondgeometry by varying the cationic occupancy and study the effect of this change on the average structure of the crystal. Thecation–anion interaction is found to have a direct influence on the O–H–O hydrogen bonds of the mixed crystals. • Crosslinked poly(ether ether ketone): cost-effective proton exchange membranes for fuel cell application Sulphonated poly(ether ether ketone) copolymers bearing pendant carboxylic acid (SPEEK-C) have beensynthesized via nucleophilic condensation reaction of 4,4$^{\prime}$-difluorobenzophenone, sulphonated 4,4$^{\prime}$-difluorobenzophenoneand 3,5-dihydroxy benzoic acid. The structure of the sulphonated copolymer was identified from FT-IR and${}^1$H-NMRspectrum. The pendant carboxylic groups of SPEEK-C were further crosslinked with poly(vinyl alcohol) (PVA) to fabricatethe crosslinked (SPEEK/PVA) membranes. The performance of the membranes was evaluated in terms of water uptake,proton conductivity and oxidative stability. The thermal stabilities of the membranes were determined by thermogravimetricanalysis and differential scanning calorimetry techniques, whereas the morphological analysis was performed by atomicforce microscopy. • Effect of$\gamma$-irradiation on the thermal properties of UHMWPE/MWCNTs nanocomposites: a comparative study of incorporating unmodified and$\gamma$-ray-modified MWCNTs The efficacy of defective sites in MWCNTs as free radical scavengers was investigated on the basis of thermalanalysis of ultra-high molecular weight polyethylene (UHMWPE)/MWCNTs and UHMWPE/$\gamma$-MWCNTs nanocomposites. Homogenized composites of polyethylene (PE) with MWCNTs and$\gamma$-MWCNTs (0.5% by weight) were prepared by the ball milling process for 2 h at a speed of 200 rpm. Thereafter, micron-sized sheets were prepared (by hot pressing) and subjected to$\gamma$-dose ranging from 25 to 150 kGy. To investigate the thermal properties and thermal stability, differential scanning calorimetric (DSC) and thermo-gravimetric analysis (TGA) measurements were performed in an inert atmosphere. Theresults showed that peak melting temperature ($T_{\rm m}$) and lamellae thickness ($L_{\rm c}$) remained unaltered for UHMWPE/MWCNTs composites; however, for UHMWPE/$\gamma$-MWCNTs composites the values varied from 138 to 141$^{\circ}$C. This behaviour was attributed to chain scission close to crystalline lamellae due to radiation-induced free radicals, thus reducing the percentage of inter-phase contents within the polymer matrix and enhancing the percentage crystallinity for composites. Furthermore, TGA revealed the higher thermal stability of composites as compared with pristine ones and significant increase in residues percentage for composites, i.e., from$\sim$3 to 7%. These results confirmed the importance of defective sites within the MWCNTs as free radical quenchers, and stopping the chain scission, particularly close to crystalline lamellae, thus preventing loss of the important interphase region of UHMWPE. • Role of surface thermal properties of HfB$_2$nanoparticles on heat flow in MWCNT/novolac composites Carbon–novolac composites (C–C) modified by HfB$_2$and MWCNT were ablated by an oxyacetylene torch at 2500$^{\circ}$C to investigate the thermal behaviour and the mechanism of mass loss of the samples. Two phenolic matrix composites containing 4 wt% HfB$_2$nanoparticle and with or without MWCNT were fabricated. These nanoparticles dissipate heatthroughout the sample, thereby reducing thermal gradients, reducing the intensity of heating at the surface exposed to flame,and insulating the carbonaceous char with the network of HfO$_2$/MWCNT/char. During ablation, HfO$_2$particles formed and functioned as a thermal barrier, and MWCNT char phase acted as an oxygen diffusion barrier, protecting composites fromfurther ablation. • Construction of CaF$_2$-appended PVA nanofibre scaffold In this work, a new material, calcium fluoride (CaF$_2$)-appended poly(vinyl alcohol) (PVA) nanofibre scaffold,was prepared through electrospinning technique successfully. Scanning electron microscopy result showed that the morphologyof the fibres was uniform and smooth, and the average diameter of the fibres was about 200 nm. Transmissionelectron microscopy results showed that many CaF$_2$nanoparticles were well dispersed in the PVA fibre matrix. The waterresistant ability of the scaffold was improved through intermolecular crosslinking of PVA by formaldehyde vapour. Thisnovel material seems to be a promising scaffold for bone tissue engineering. • Dielectric properties study of surface engineered nanoTiO$_2$/epoxy composites Nanodielectrics are promising materials that can efficiently store a large amount of electrical energy that aredesirable for many electronic and power devices. Control of polymer–particle interface in nanodielectrics is very critical innot only obtaining the improved quality of dispersion but also in altering the dielectric properties. Various surface modifyingagents with linear (alkyl), aromatic (phenyl) and extended aromatic (naphthyl) chemical nature were employed at the epoxy–nanoTiO$_2$interface. All the surface-modifying agents were successful in passivating the nanoparticles surface and in obtaining the improved quality of polymer–particle dispersion and improved glass transition temperature comparatively. However, allthe surface modifiers were not successful in obtaining the improved dielectric properties of the nanodielectrics, especiallydielectric breakdown resistance. Only the extended aromatic group at the polymer–particle interface, which is more electronwithdrawing in electronic nature than phenyl and alkyl structures, was successful in improving the dielectric breakdownresistance. Thus, the choice of surface-modifying agent based on its chemical and electronic nature is very important inoptimizing the dielectric properties of nanodielectrics. Naphthyl phosphate-modified nanoTiO$_2$–epoxy composite films of$\sim$90–100$\mu$m thick at 5 vol% particle concentration yielded higher dielectric breakdown resistance than pure epoxy polymer and thereby resulted in about 90% higher electrical energy storage density than the pure epoxy film. • Polyphenol oxidase-based luminescent enzyme hydrogel: an efficient redox active immobilized scaffold A novel, functionally potent polyphenol oxidase (10000 U)-mediated urchin-shaped composite-basedluminescent enzyme hydrogel network as immobilized scaffold for oxido-reductase efficiency on phenolic substrates includingphenol, resorcinol, catechol and quinol was synthesized and characterized through fluorescence spectroscopy along withscanning electron microscopy and transmission electron microscopy. • Estimation of particle size distribution of nanoparticles from electrical characteristics An indirect method of estimation of size distribution of nanoparticles in a nanocomposite is proposed inthis paper. The present approach exploits DC electrical current–voltage characteristics (CVC) of ZnO nanocompositespecimen in bio-polymer background. The nature of DC CVC is found to be oscillatory with respect to applied voltage.The nature of CVC is a consequence of Coulomb blockade (CB) phenomena of electrical conduction through atiny nanoparticle. Considering the ZnO nanocomposites to be spherical, Coulomb-blockade model of quantum dot isapplied here. The size distribution of particle is estimated from that model and compared with the results obtainedfrom AFM and XRD analyses. The results from CVC are found to be consistent with these conventional microscopicresults. • Influence of the conditions of a solid-state synthesis anode material Li$_4$Ti$_5$O$_{12}$on its electrochemical properties of lithium cells Lithium–titanium spinel is a promising electrode material for high power and environmentally friendly batteries.We did research on Li$_4$Ti$_5$O$_{12}$(LTO) samples, which were synthesized via solid-state reaction at various conditions in atemperature range from 800 to 900$^{\circ}$C and they were investigated by XRD, SEM, IS, cyclic voltammetry and the galvanostatic charge–discharge tests. X-ray diffractions show that all of the samples have a spinel structure with Fd-3m space group with a small amount of impurities TiO$_2$(anatase). Lithium ion batteries with LTO-based electrode exhibit excellent reversiblecapacity of$\sim$180 mAh g$^{−1}$in the current density range from 0.1 to 1 C. As an electrode material for rechargeable lithium-ion batteries, LTO-F demonstrates the best rate and cyclic performance from all of the studied samples. • Factorial design, processing, characterization and microstructure analysis of PIP-based C/SiC composites Polymer impregnation and pyrolysis (PIP) process-based C/SiC composites are fabricated using the in-housesynthesized methyl-polycarbosilane (PCS). Two-level factorial design matrix is employed to carry out experiments to studythe effect of four factors on flexural strength of the composite.Total sixteen sets of composite samples are fabricated.Responsetable, normal probability plot, ANOVA and regression analysis are carried out to determine the statistical significant factors.Composite density ($\rho$), fibre volume fraction ($V_{\rm f}$) and pyrolysis temperature ($T$) are found to be statistically significant, while softening point (SP) of the PCS and interaction of these four factors are found insignificant. Higher levels of thedensity and$V_{\rm f}$have shown positive effect, while the pyrolysis temperature has negative effect on the flexural strength of the composites. Flexural strength was found to be in the range of 374–592 MPa depending on the process parameters. Themechanical behaviour of the composites at different process conditions was explained with the help of their microstructures. • Advanced nanofibrous textile-based dressing material for treating chronic wounds In the present work, an electrospun nanofibrous textile composed of polyurethane (PU), sodium bicarbonate(NaHCO3) and pantothenic acid (PA) is developed for treating chronic wounds. Wounds are a common health problemand in particular, the chronic wounds such as vascular ulcers, diabetic ulcers and pressure ulcers cause a large number ofmorbidity and mortality. The main problems of the chronic wounds are prolonged inflammation phase and presence of acidicenvironment. These events deactivate the operation of growth factors and also the progression of natural healing mechanism.Hence, various types of advanced textile-based dressings are developed to address the clinical complications associated withchronic wound management. The prepared electrospun scaffolds were characterized to study their physicochemical andhaemocompatible properties. The scanning electron microscopy micrographs depicted continuous, smooth-interconnectednanofibrous morphology of PU–NaHCO$_3$–PA scaffolds. The Fourier transform infrared spectroscopy spectra indicatedthe addition of NaHCO$_3$and PA-based hydrophilic chemical groups, which significantly enhanced the wettability of thecomposites. Further, the PU–NaHCO$_3$–PA composite membrane inferred to have a highly porous structure with the mean porosity of 79.4$\pm$4.8%, which may provide a conducive environment for adherence and proliferation of skin cells. The composite scaffold also offers a highly haemocompatible surface by delaying coagulation of blood through contact activationpathways and by limiting red blood cells damage. Therefore, the excellent physicochemical properties, blood compatibilityand the delivery of PA are anticipated to speed up the impaired healing process of chronic wounds. • Elastic and thermodynamic properties of zirconium- and hafnium-doped Rh$_3$V intermetallic compounds: potential aerospace material Structural, electronic, mechanical and thermodynamic properties of Rh$_3$Zr$_x$V$_{1−x}$and Rh$_3$Hf$_x$V$_{1−x} ($x = 0$, 0.125, 0.25, 0.75, 0.875 and 1) combinations are investigated by means of first-principles calculations based on the density functional theory within the generalized gradient approximation. Here, Rh$_3$V is chosen as the parent binary compound and the doping elements are zirconium and hafnium with the above-mentioned concentrations. The calculated lattice parameters and elastic modulus of binary Rh$_3$Hf, Rh$_3$V and Rh$_3$Zr are in good agreement with the available experimental and other theoretical results. In this study, the following ternary materials viz., Rh$_3$Zr$_{0.75}$V$_{0.25}$, Rh$_3$Hf$_{0.25}$V$_{0.75}$ and Rh$_3$Hf$_{0.75}$V$_{0.25}$ are found to be brittle/more brittle than the parent binary compound Rh$_3$V, whereas the other ternary combinations, namelyRh$_3$Zr$_{0.125}$V$_{0.875}$, Rh$_3$Zr$_{0.25}$V$_{0.75}$, Rh$_3$Zr$_{0.875}$V$_{0.125}$, Rh$_{3}Hf$_{0.125}$V$_{0.875}$and Rh$_3$Hf$_{0.875}$V$_{0.125}$are found to be more ductilethanRh3V. The more brittle ternary combination, namely Rh$_3$Hf$_{0.75}$V$_{0.25}$($B = 229.32$GPa) has the maximum Young’s modulus,shear modulus and hardness values; whereas the more ductile ternary Rh$_3$Zr$_{0.25}$V$_{0.75}$combination ($B = 243.54$GPa) is found to have the least values of Young’s modulus, shear modulus and hardness. The band structure, density of stateshistograms and charge density plots are drawn and discussed. Computed Debye temperature (θD), Grüneisen parameter ($\zeta$) and melting temperature ($T_{\rm m}$) of the parent binary compound Rh$_3$V, the more brittle Rh$_3$Hf$_{0.75}V$_{0.25}$ combination and themore ductile Rh$_3$Zr$_{0.25}$V$_{0.75}$ combination are given by (895 K, 1.3491, 2788 K), (790 K, 1.2701, 2736K) and (698 K, 1.7972, 2529 K), respectively.

• Influences of nonsolvent on the morphologies and electrochemical properties of carbon nanofibres from electrospun polyacrylonitrile nanofibres

The influences of nonsolvent on the morphologies and electrochemical properties of carbon nanofibres (CNFs)obtained via pre-oxidation and carbonization of electrospun polyacrylonitrile (PAN) nanofibres were mainly studied.Volatilemethanol (MeOH) and acetonitrile (MeCN) were introduced into PAN solutions as the nonsolvent for PAN, which mayproduce porous structures via inducement of phase separation. The morphologies of the prepared nanofibres were observed viascanning electron microscopy. It was found that PAN nanofibres possessed corrugated and rough surfaces. PAN fibres obtainedin the presence of nonsolvent showed larger diameters and wider distributions than those obtained without nonsolvent. Afterthermal treatments, inter-bonded CNFs were prepared. The structures of CNFs were confirmed by X-ray diffraction andRaman spectrometry. Then the electrochemical properties of CNFs were examined by an electrochemical method in a threeelectrodesystem. Based on chronopotentiometry, CNFs exhibited the highest capacity up to 198 F g$^{−1}$ at current density of3 A g$^{−1}$. The influence rule of nonsolvents on the morphology and capacities of CNFs was summarized and interpreted.

• Effect of alumina coating and extrusion deformation on microstructures and thermal properties of short carbon fibre–Al composites

Short carbon fibres were coated with alumina by sol–gel process. Uncoated and alumina-coated short carbonfibre–Al composites were fabricated by gas pressure infiltration process. The effects of alumina coating and extrusiondeformation on microstructures and thermal properties of the composites were studied. The results showthat alumina coatingis effective to improve the quality of the short carbon fibre preform as well as act as diffusion barrier to impede interfacialharmful chemical reactions between aluminium and short carbon fibres, which would increase the thermal properties ofthe composites. Extrusion deformation can orient the carbon fibres to the extrusion direction to improve their degree oforientation, meanwhile decreasing their aspect ratio. Extrusion deformation has a beneficial effect on the thermal conductivityof the composites. However, its effect on coefficient of thermal expansion of the composites is small because the effects ofthe improvement in degree of orientation and the decrease of aspect ratio tend to cancel each other somewhat.

• Effect of annealing atmosphere on microstructure, optical and electronic properties of spray-pyrolysed In-doped Zn(O,S) thin films

Spray-pyrolysed zinc oxy-sulphide Zn(O,S) has been doped with varying concentrations of indium (In) toimprove its electrical and optical properties for possible application as buffer layer in thin film solar cells. The In-dopingin Zn(O,S) is found to change the electron carrier concentration from 10$^{19}$ to 10$^{18}$ cm$^{−3}$ and a subsequent annealing in argon atmosphere is found to improve its electrical conductivity. Moreover, annealing in air atmosphere reduces the carrier concentration to a range of 10$^{13}$–10$^{15}$ cm$^{−3}$ making it useful as a buffer layer. The reduction in degeneracy of In-doped Zn(O,S) is desirable for its application as buffer material, whereas annealing in argon makes it suitable as electron membrane (window layer) in thin film solar cell.

• Superconducting epitaxial YBa$_2$Cu$_3$O$_{7−\delta}$ on SrTiO$_3$-buffered Si(001)

Thin films of optimally doped(001)-oriented YBa$_2$Cu$_3$O$_{7−\delta}$ are epitaxially integrated on silicon(001) through growth on a single crystalline SrTiO$_3$ buffer. The former is grown using pulsed-laser deposition and the latter is grown on Si using oxide molecular beam epitaxy. The single crystal nature of the SrTiO$_3$ buffer enables high quality YBa$_2$Cu$_3$O$_{7−\delta}$ films exhibiting high transition temperatures to be integrated on Si. For a 30-nm thick SrTiO$_3$ buffer, 50-nm thick YBa$_2$Cu$_3$O$_{7−\delta}$ films that exhibit a transition temperature of $\sim$93 K, and a narrow transition width (<5 K) are achieved. The integration ofsingle crystalline YBa$_2$Cu$_3$O$_{7−\delta}$ on Si(001) paves the way for the potential exploration of cuprate materials in a variety of applications.

• A logical explanation of structurally unfit X-ray diffraction peaks in nanoferroelectrics

In the present paper we suggest the cause and solution of some unidentified X-ray diffraction (XRD) peaks inferroelectric nanoparticles. Indeed, a relationship between the structurally unfit XRD peaks and domains in the ferroelectricnanoparticles is suggested. BaTiO$_3$, PbTiO$_3$ and Sr$_{0.5}$Ba$_{0.5}$Nb$_2$O$_6$ nanoparticles were used as trial samples. Diffraction of X-rays by domain grating was considered for the occurrence of unfit peaks. It was found that domain widths corresponding to some structurally unfit minor peaks of all three trail samples show good agreement to the values estimated from the transmission electron microscopy images. The study can be used to estimate the width of nanodomains (within 5–10 $\AA$) in ferroelectric nanoparticles. Thus, the study seems to be highly important for the advancement of nanoferroelectricity.

• Structural characterization and properties of YCrO$_3$ nanoparticles prepared by reverse micellar method

YCrO$_3$ nanoparticles were prepared by reverse micellar method by the use of surfactant tergitol after heating theprecursor sample at 800$^{\circ}$C. As-prepared YCrO$_3$ nanoparticles were characterized by various sophisticated techniques like X-ray diffraction (XRD), transmission electron microscope, Brunauer–Emmett–Teller surface area analyzer, high frequency LCR-meter, superconducting quantum interface device magnetometer and P–E loop tracer. Powder XRD study revealsthe formation of highly crystalline orthorhombic monophasic YCrO$_3$ nanoparticles. The average grain size of as-preparednanoparticles was found to be 35 nm with the surface area of 348 m$^2$ g$^{−1}$.Wedge-shaped hysteresis for ferromagnetism andthe room temperature ferroelectricity confirm the multiferroic characteristics in the nanoparticles.

• NO$^−_2$ and SCN$^−$-intercalated layered double hydroxides: structure and orientation of anions in the interlayer gallery

NO$^−_2$ and SCN$^−$ are two common small inorganic anions. The former is a common industrial pollutant. Thelatter is linear and is a good mimic for the toxic CN$^−$ ion. The structures of these two anions are refined within the gallery ofthe [Zn–Al]-layered double hydroxide (LDH). Both LDHs crystallize as mixed anion phases. The nitrite is found to co-existwith the nitrate ion. The nitrite ion is intercalated with its molecular plane inclined to the metal hydroxide layer. In the caseof the SCN$^−$ intercalated LDH, no other anion was detected by ion chromatography, suggesting that the SCN$^−$ deficiencyis compensated by intercalated hydroxyl ions. In this case, the SCN$^−$ ion is found to be intercalated with its molecular axisinclined to the metal hydroxide layer.

• TiO$_2$ aerogel–metal organic framework nanocomposite: a new class of photoanode material for dye-sensitized solar cell applications

TiO$_2$ aerogel–metal organic framework (MOF) nanocomposite was synthesized using sol–gel method followedby subcritical drying technique and employed as a photoanode material in quasi-solid dye-sensitized solar cells (DSSCs). Thenanocomposite material showed aBET surface area of 250 m$^2$ g$^{−1}$ with an average pore size of 5 nm. Field emission scanning electron microscopic images revealed the continuous arrangement of pore-solid network structure. Energy-dispersive X-ray analysis shows the presence of MOF clusters on TiO$_2$ aerogel network. X-ray photoelectron spectroscopic analysis alsosupports the presence of MOF clusters in the aerogel network and indicates the presence of some oxygen vacancies in thenanocomposite material. The TiO$_2$ aerogel–MOF nanocomposite was used as photoanode in DSSC and an overall power conversion efficiency 2.34% along with a short circuit current density 6.22 mA cm$^ {−2}$ was achieved.

• Development and properties of advanced composites based on cork and nanometric silicon carbide-filled phenolic resin

This paper presents the obtaining of advanced materials based on cork powder as reinforcement and phenolic resin (PR) with silicon carbide (nSiC) nanofiller as matrix with potential applications in aerospace industry. Three formulationswere obtained: one control sample PR/cork with no nanofiller, two nanofilled samples with 1 and 2 wt% nSiC loadings into the resin. The materials were tested by flexural and compressive mechanical tests to determine their strength and stiffness, to determine their friction coefficient by tribological tests, to determine their thermal decomposition behaviour by TG-DSC analysis and to evaluate their thermal behaviour by thermal shock tests when subjected to extreme temperature directly from room temperature. The material structure was analysed by SEM visualizing the fracture cross-section after mechanical testing. The test results illustrate that silicon carbide nanoparticles improve flexural and compressive strength, but also stiffness and friction coefficient, delay thermal decomposition onset and improve thermal shock resistance. All these sustain the PR/nSiC/cork materials as potential advanced materials candidates for thermal protection applications.

• A focus on the features of polyaniline nanofibres prepared via developing the single crystals of their block copolymers with poly(ethylene glycol)

Poly(ethylene glycol) (PEG)–polyaniline (PANI) diblock and triblock copolymers were synthesized viacopolymerization of aniline with amine-terminated PEG by interfacial polymerization using sulphuric acid as dopant andammonium peroxydisulfate (APS) as well as potassium hydrogen diiodate (PHD) as oxidants. The PHD-based synthesizedPANI nanorods possessed longer lengths, narrower diameter distribution and higher conductivity. The electroactivity ofsynthesized copolymers was characterized using ultraviolet–visible (UV–Vis) spectrometry, cyclic voltammetry (CV) andresistivity measurement. Even in the presence of dielectric PEG blocks, the synthesized block copolymers had a conductivityaround 3 S cm$^{−1}$. In a further step, the solution-grown single crystals were prepared to investigate the general features ofgrafted PANI nanorods using small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and atomicforce microscopy (AFM). Based on AFM and SAXS analyses, the bimodal gel permeation chromatography (GPC) tracesobtained from the block copolymers were originated from the diameter distribution of nanofibres, not from the dispersity oftheir lengths and molecular weights.

• Templated, carbothermal reduction synthesis of mesoporous silicon carbide from carbon nanotube–mesoporous silica core–shell composite

Mesoporous materials are the subject of extensive interest due to their large surface area and multiscale structuralorder. These properties are especially relevant for applications such as catalyst supports in both chemical and electrochemicalsystems. The first part of this study details the synthesis of carbon nanotube–mesoporous silica core–shell composites startingwith single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) through micellar selfassembly.The formation of such a composite structure was verified using scanning electron microscopy and further analysiswas carried out through X-ray diffraction (XRD). The subsequent refinement of the diffraction pattern revealed the silicashell to be of the continuous cubic (Ia3d) MCM48 structure. The mesoporous silica–carbon nanotube core–shell composite was later subjected to high-temperature carbothermal reduction. Subsequent XRD analysis showed that the reduction product was mesoporous silicon carbide (SiC). Thus, this study details a novel synthesis method for mesoporous SiC, which is anattractive material for possible diverse applications such as catalyst supports, intercalation electrodes and other emerginghigh technology areas.

• Formation and densification of mullite through solid-oxide reaction technique using commercial-grade raw materials

Two different commercially available sources of alumina and silica were used to study the formation and densificationbehaviour of mullite prepared by solid-oxide reaction technique in a single firing. Phase analysis and densificationstudies were carried out on the samples sintered between 1200 and 1600$^{\circ}$C. Effect of addition of 1–6 wt% MgO on thesintered mullite ceramics was also studied.MgO was found to improve the density values for all the compositions till 4 wt%and with higher addition it deteriorated, mainly due to higher extent of liquid phase formation. Mullite formation was foundto start below 1200$^{\circ}$C and constituent oxides were found even at 1600$^{\circ}$C; however, addition of 4 wt% MgO was found to complete the mullite formation at 1600$^{\circ}$C for all the compositions. Microstructural studies showed grain growth in the compositions containing MgO and higher impurities due to formation of greater extent of liquid phase.

• Studies on $n$- and $p$-type metal oxide compounds for thermoelectric device fabrication

We report the high-temperature thermoelectric properties of electron- and hole-doped calcium manganese oxidematerials, which exhibit potential of a thermoelectric device for conversion of wasteful thermal energy into useful electricalenergy. Electron-doped Ca$_{0.9}$R$_{0.1}$MnO$_3$ (R $=$ La, Yb) and hole-doped Ca$_4$Mn$_{2.85}$Nb$_{0.15}$O$_{10}$ manganites chosen for the present study were prepared by solid-state reaction of starting compounds and characterized by powder X-ray diffraction. Electrical resistivity and thermopower were measured as a function of temperature to determine the power factor for all the three compounds studied. We discuss these results according to their application potential as a thermoelectric device.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019