• Volume 40, Issue 5

September 2017,   pages  877-1047

• Structural, thermal and optical properties of Cu$^{2+}$ doped methacrylic acid–ethyl acrylate (MAA:EA) copolymer films

Pure and Cu$^{2+}$ doped methacrylic acid–ethyl acrylate (MAA:EA) copolymer films were prepared using thesolution cast technique. The amorphous feature of the copolymer was depicted using X-ray diffraction scans and degreeof crystallinity was found to vary with increasing doping content. UV–Vis absorption spectra in the wavelength region200–900 nm were used to evaluate the optical properties like direct band gap, indirect band gap and absorption edge. Theoptical band gap decreased with the increase of mol% of Cu$^{2+}$ ions. Fourier transform infrared spectral studies on pureMAA:EA and Cu$^{2+}$ ions-doped films revealed the vibrational changes that occurred due to the effect of dopant salt inthe copolymer. Thermal properties of these films were investigated by employing differential scanning calorimetry andthermogravimetric analysis. The variation in film morphology was examined by scanning electron microscopy. Electronparamagnetic resonance (EPR) spectra of all the doped samples exhibited signals due to Cu2+ ions with the effective$g$-values $g_{\parallel} = 2.177$ and $g_{\perp} = 2.058$. The observed variation in the EPR signal intensity is due to the isolated and aggregated copper ions. The photoluminescence spectra of Cu$^{2+}$ ions-doped MAA:EA copolymer exhibited four emissionpeaks at 480 (blue), 579 (yellow), 604 (red) and 671nm (red).

• Structural, microstructural and optical properties of Cu$_2$ZnSnS$_4$ thin films prepared by thermal evaporation: effect of substrate temperature and annealing

Thin films of Cu$_2$ZnSnS$_4$ (CZTS), a promising solar cell absorber, were grown by thermal evaporation ofZnS, Sn and Cu precursors and subsequent annealing in sulphur atmosphere. Two aspects are chosen for investigation:(i) the effect of substrate temperature ($T_S$) used for the deposition of precursors and (ii) (N$_2$ $+$ S$_2$) pressure during annealing, to study their impact on the growth of CZTS films. X-ray diffraction analysis of these films revealed the structure to be kesterite with (112) preferred orientation. Crystallite size is found to slightly increase with increase in TS as well as pressureduring annealing. From optical absorption studies, the direct optical band gap of CZTS films is found to be $\sim$1.45 eV. Room temperature electrical resistivity of the films obtained on annealing the stacks at 10 and 100 mbar pressures is found to be in the ranges 25–55 and 5–25 cm, respectively, depending on $T_S$. Films prepared by annealing the stack deposited at 300$^{\circ}$C under 100 mbar pressure for 90 min are slightly Cu-poor and Zn-rich with compact grain morphology.

• Anisotropic optical properties of ZnS thin films with zigzag structure

ZnS sculptured thin films produced by thermal evaporation method using the glancing angle deposition techniqueat different deposition angles (0, 30, 60, 70 and 80$^{\circ}$) are reported. The structural and optical properties of the prepared samples are investigated systematically using X-ray diffraction (XRD) and UV–VIS spectroscopy techniques. The XRD studies show cubic structure for the prepared films and deposition angle dependence of lattice constants, intrinsic stress, tensile stress anddislocation density. The obtained transmittance spectra in the range 380–850 nm for both s- and p-polarized light at normalincidence angle are used to study the s- and p-refractive indices and in-plane birefringence of the ZnS films. The maximumbirefringence is evaluated at incident flux angle α = 70$^{\circ}$. Both the refractive index and packing density of the films decreasewith increasing deposition angle, which confirm the structural inhomogeneity and porosity nature of the films.

• Electro-optical properties, decomposition pathways and the hydrostatic pressure-dependent behaviours of a double-cation hydrogen storage material of Al$_3$Li$_4$(BH$_4$)$_{13}$

Electro-optical properties, the decomposition pathways and the pressure-dependent behaviours of Al$_3$Li$_4$(BH$_4$)$_{13}$ have been investigated using a first-principle plane-wave pseudopotential method. Al$_3$Li$_4$(BH$_4$)$_{13}$ is a kindof double-cation borohydride, consisting of distorted tetrahedral anions [Al(BH$_4$)$_4$]$^−$ and cations [Li$_4$(BH$_4$)]$^{3+}$, which obeys the stability criteria of decomposition reactions. Herein, two possible decomposition reactions of the compound are proposed, which release 18 hydrogen molecules (about 12.03 wt%) in the first reaction and 24 hydrogen molecules (about16.04 wt%) in the second reaction. On increasing the pressure on the structure, the lattice parameter, the volume of unitcell, the quasiparticle band gap and also enthalpy of the system decrease nearly monotonically; therefore, the acceptor levelsgradually get filled and the Fermi level shifts upward. Results of computational investigations of the structural, electronic andthermodynamic parameters and their pressure-dependent behaviours indicate that Al$_3$Li$_4$(BH$_4$)$_{13}$ has intriguing properties. Therefore, it would be a very promising material for hydrogen storage technology.

• Synthesis, structural and dielectric properties of 0.8PMN–0.2PT relaxor ferroelectric ceramic

A 0.8PMN–0.2PT solid-solution ceramic was synthesized by columbite processing technique. The effects ofsintering temperature on the density, structure and microstructure and in turn on the dielectric properties were investigated.The ceramics sintered at and above 1050$^{\circ}$C resulted in single-phase perovskite formation. However, high density $>$90% is achieved only after 1170$^{\circ}$C. Microstructural analysis revealed that grain size increases with increase in sintering temperature. Asignificant increase in the peak of dielectric permittivity only after 1150$^{\circ}$C owing to increase in density is noted in this study. The quadratic law applied to this ceramic demonstrates that the transition is diffused. The broadness in phase transition and lower dielectric relaxation obtained for the composition demonstrate that the ceramic exhibits characteristics of both relaxor and normal ferroelectrics. The ceramic of composition 0.8PMN–0.2PT exhibits excellent dielectric properties $\epsilon_{\rm r-max} = 20294$−27338 at 100 Hz with $T_c = 100$–96$^{\circ}$C at low sintering temperature 1170–1180◦C, respectively.

• Structural, dielectric and piezoelectric study of Ca-, Zr-modified BaTiO$_3$ lead-free ceramics

We prepared a lead-free ceramic (Ba$_{0.85}$Ca$_{0.15}$)(Ti$_{1−x}$Zr$_x$ )O$_3$ (BCTZ) using the conventional mixed oxide technique. The samples were prepared by an ordinary mixing and sintering technique. In this study we investigated howsmall amounts of Zr$^{4+}$ can affect the crystal structure and microstructure as well as dielectric and piezoelectric propertiesof BaTiO$_3$. X-ray diffraction analysis results indicate that no secondary phase is formed in any of the BCTZ powders for$0 \leq x \leq 0.1$, suggesting that Zr$^{4+}$ diffuses into BaTiO$_3$ lattices to form a solid solution. Scanning electron microscopy micrographs revealed that the average grain size gradually increased with Zr$^{4+}$ content from 9.5 $\mu$m for $x = 0.02$ to 13.5 $\mu$m for $x = 0.1$; Curie temperature decreased due to the small tetragonality caused by Zr$^{4+}$ addition. Owing to the polymorphic phase transition from orthorhombic to tetragonal phase around room temperature, it was found that the composition $x = 0.09$ showed improved electrical properties and reached preferred values of $d_{33} = 148$ pC N$^{−1}$ and $K_p = 27$%.

• Role of MnO in manganese–borate binary glass systems: a study on structure and thermal properties

Structural and thermal properties of $x$MnO−($100−x$)B$_2$O$_3$ (where $x = 40, 50$ and 60 mol%) glass samples have been investigated with the employment of various techniques. Fourier transform infrared spectroscopy results revealed the influence of MnO on glass matrix. Decrease of B–O bond-related band intensities has been observed. MnO addition was found to introduce broken [BO$_2$O$^−$]$_n$ chains. Differential scanning calorimetry (DSC) measurements presented decreasing $T_g$ that indicates depolymerization of glass matrix in the considered compositional range. Moreover, thermal stability (TS) parameter has been evaluated using the DSC technique. It slightly decreased with MnO content. X-ray photoelectron spectroscopy results provided the evidence for Mn$^{2+}$ and Mn$^{3+}$ presence. Multiplet splitting, close to that of MnO, has been observed. It has been concluded that most of the manganese ions existed in the divalent state. Photoluminescence study revealed that manganese ions are tetragonally co-ordinated in a glassy matrix.

• Formation of Mg$_2$C$_3$ phase in N220 nanocarbon containing low carbon MgO-C composition

This paper reports a non-conventional microstructurewith sequicarbide (Mg$_2$C$_3$) formation in N220 nanocarboncontaining low carbon magnesia carbon composition having magnesium metal powder as antioxidant. 5 wt% graphitecontaining MgO-C refractory with and without 1 wt% N220 nanocarbon is studied and 2 wt% magnesium metal powder isused as the lone antioxidant. The compositions were mixed with powder and liquid resin binder, pressed uniaxially at 150MPa and cured at 220$^{\circ}$C. Cured samples were coked at 1000$^{\circ}$C for 2 h. Matrix of the coked samples was studied in detail for microstructural analysis phase content and formation of nail-shaped sequicarbide was found in the nanocarbon containing compositions. The in-situ sequicarbide formation has resulted in the strength of the batch.

• Influence of nanotube content on the mechanical and thermo-mechanical behaviour of –COOH functionalized MWNTs/epoxy composites

Functionalized multi-wall carbon nanotubes (MWNTs) with carboxylic acid group (–COOH) have been utilizedfor the preparation of epoxy nanocomposites. Composites were synthesized using three different wt% (0.5, 0.75 and 1) ofMWNTs via the solution mixing technique followed by ultrasonication. Mechanical and thermo-mechanical properties ofthe fabricated composites have been experimented for the suitability of this material in a variety of structural applications.The flexural modulus, strength, hardness, impact strength and storage modulus increased upon increasing MWNTs contents.Best results have been observed in nanocomposites with 0.75 wt% nanotubes loading, which showed 101, 166 and 61%enhancement in the flexural modulus, hardness and storage modulus, respectively, compared to neat epoxy. Achievementof uniform dispersion and hence formation of improved interface between nanotubes and epoxy was the reason behindthe maximum enhancement at this wt%, which is further evidenced by the fracture surface morphology obtained frommicroscopical investigations.

• Poly(acrylonitrile-co-itaconic acid)–poly(3,4-ethylenedioxythiophene) and poly(3-methoxythiophene) nanoparticles and nanofibres

This work aimed to produce poly(acrylonitrile-co-itaconic acid) (P(AN-co-IA)) nanocomposites with poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3-methoxythiophene) (PMOT). An anionic surfactant sodium dodecyl benzenesulphonate was used in emulsion polymerization for nanocomposite production. Incorporations of PEDOT and PMOT on the nanoparticles were characterized by scanning electron microscopy (SEM), atomic force microscopy, Fourier transforminfrared-attenuated total reflectance spectroscopy and ultra-violet spectroscopy. These nanoparticles were blended withPAN and the blends were electrospun to produce P(AN-co-IA)–polythiophene-derivative-based nanofibres, and the obtainednanofibres were characterized by SEM and energy dispersive spectroscopy. In addition, electrochemical impedance studiesconducted on nanofibres showed that PEDOT and PMOT in matrix polymer P(AN-co-IA) exhibited capacitive behaviourcomparable to that of ITO–PET. Their capacitive behaviour changed with the amount of electroactive polymer.

• In-situ microfibrillar PP–PA6 composites: rheological, morphological and mechanical properties

In this study, the rheology, morphology and mechanical properties of microfibrillar composites based onpolypropylene reinforced with polyamide 6 (PA6) fibres have been investigated. Influence of different factors such as thePA6 composition and drawing ratio on the output of the extruder, and the compatibilizer composition on the properties ofthese composites, were investigated. The results of rheometric mechanical spectrometer rheological measurements and meltflow index (MFI) showed that the storage modulus, loss modulus and complex viscosity of the microfibrillar composites aredirectly related to the composition of PA6. It was also shown that the presence of compatibilizer was the main factor that ledto decrease of some properties including the storage modulus, loss modulus and complex viscosity and increase in the MFI.The results of mechanical tests on samples prepared with different drawing ratios showed that by increasing the drawing ratiofrom 3 to 5, the mechanical properties increase, while increasing draw ratio from 5 to 8 reduces the mechanical properties.With the increase in the composition of the polyamide phase, the tensile strength of microfibrillar composite compatible withpolypropylene-grafted-maleic anhydride initially increased; however, the tensile strength decreased with a high compositionof polyamide phase. Scanning electron microscope images also revealed that the presence of the compatibilizer in themicrofibrillar composites leads to decrease in the number of undeformed drops, while it reduces the micro-fibres diameter,which greatly improved the final properties of the composites.

• Fabrication and enhanced photoluminescence properties of NaLa(MoO$_4$)$_2$: Sm$^{3+}$, Bi$^{3+}$ phosphors with high efficiency white-light-emitting

The tetragonal scheelite-type Sm$^{3+}$/Bi$^{3+}$ ions co-doped with NaLa(MoO$_4$)$_2$ phosphors were synthesized by a facile sol–gel and combustion process using citric acid as complexing agent. The crystal structure and morphology of theseas-prepared samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Furthermore,UV-absorption and the photoluminescence (PL) properties of these phosphors were systematically investigated and the PLof the phosphors shows strong white light emissions. Efficient energy transfer from the MoO$^{2-}_4$ group or Bi$^{3+}$ ions to Sm$^{3+}$ ions was established by PL investigation excited at 405 nm. The PL intensity of the studied materials was investigated asa function of different Sm$^{3+}$ and Bi$^{3+}$ concentrations. The PL investigations revealed that the phosphors exhibit apparentcharacteristic emissions, which is ascribed to the transition from the ground state energy level 4G5/2 to excited state energylevels ${}^6$H$_J$ ($J = 5/2$, 7/2, 9/2) and the NaLa(MoO$_4$)$_2$: 4 mol% Sm$^{3+}$ and NaLa(MoO$_4$)$_2$: 4 mol% Sm$^{3+}$, 8 mol% Bi$^{3+}$ present white emissions with the CIE coordinates of (0.350, 0.285) and (0.285, 0.229), respectively. The absolute quantum efficiencies of the phosphors are 40% (NaLa(MoO$_4$)$_2$: 4 mol% Sm$^{3+}$) and 52% (NaLa(MoO$_4$)$_2$: 4 mol% Sm$^{3+}$, 8 mol% Bi$^{3+}$), respectively.

• Optical spectroscopy of rare earth-doped oxyfluoro-tellurite glasses to probe local environment

TeO$_2$-based glasses with a general formula 65TeO$_2$−5BaF$_2$−30ZnF$_2$ (TBZ) (in mol%) were prepared by usual melt quenching technique. Three mol% of europium (Eu) or erbium (Er) were added to the prepared glass at the expense of TeO$_2$. Raman, photoluminescence (PL), UV–visible absorption studies were carried out on the glass samples. Raman spectra of the undoped and doped glasses were analysed using the peak shift and the intensity variation along with fullwidth at half-maximum (FWHM). It was found that Eu-doped TBZ glass has a greater tendency towards depolymerizing theglass matrix by influencing the conversion of TeO$_4$ to TeO$_3$ units compared to Er-doped and undoped glasses. PL spectraof the glass samples show emission due to different possible transitions. Position of the peak of the de-convoluted spectrashows the position of the particular Stark component and the FWHM is a measure of the inhomogeneous broadening. TheUV–visible absorption spectra are used to calculate the optical density and to determine the band edge of the glass samplesby fitting to the Mott equation. It is seen that Eu-doped TBZ glass has a lesser bandgap than that of Er-doped glass.

• A comparative property investigation of lithium phosphate glass melted in microwave and conventional heating

The present study addresses the application of microwave (MW) energy for melting lithium phosphate glass. Acomparative analysis of the properties is presented with glasses melted in conventional resistance heating adopting standardmethods of characterization. The density of the glass was found less in MW heating. The glass transition temperature wasrecorded as 3–10$^{\circ}$C lower in MW prepared glass than in conventional glass.Micro-hardness is found to be improved in caseof MW heating. Maximum forward power was recorded less than 2 kW with an average power $\sim$1 kW during melting of40 g glass in MW furnace. MW forward and reflected power measured during melting in the MW cavity was elaborated.Total melting time was within 2 h 30 min in MW heating, whereas it was 6–7 h in resistive heating. Total power consumedwas $\sim$5 kWh in MW heating and $\sim$14 kWh in resistance heating.

• Structural and magnetic studies on copper succinate dihydrate single crystals

Single crystals of copper succinate dihydrate were grown in silica gel by slow diffusion of copper chloride tosodium metasilicate gel impregnated with succinic acid. The grown crystal was subjected to single crystal X-ray diffractionstudies. In its structure each copper atom is penta co-ordinated to oxygen atoms of four succinate oxygens and oxygenof co-ordinated water molecule. The four bis-bidendate succinate anions form syn–syn bridges among two copper atomsto form a polymeric two-dimensional chain. From room temperature vibrating sample magnetometer (VSM) studies themagnetic moment of the material is calculated as 1.35 Bohr magneton (BM), indicating antiferromagnetic interaction betweencopper atoms and can be explained as due to the orbital overlap of the bridging ligand and the two copper atoms in syn-synorientation. A strong bonding of the magnetic orbital of equatorially oriented Cu atom on both sides of the exchange pathway(Cu–O-C-O–Cu) leads to the anti-ferromagnetic interaction.

• The use of biodegradable polymers for the stabilization of copper nanoparticles synthesized by chemical reduction method

Copper nanoparticles were synthesized by a convenient and rapid chemical reduction method in ambient condition using Cu(NO$_3$)$_2$·${}^{3}$H$_2$O as a precursor, hydrazine hydrate as reducing agent and deionized water as solvent.The product was characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy, Fouriertransform infrared spectroscopy and UV–Vis spectroscopy. However, agglomerated copper nanoparticles were obtained bythis chemical reduction method. Hence, the effects of three polymers of polyvinyl pyrrolidone, polyethylene glycol (PEG)and starch as stabilizers on the size and size distribution of Cu nanoparticles were investigated. According to the results,smallest copper nanoparticles (30–50 nm) with a narrowsize distributionwere obtained using PEG as the stabilizing polymer.Zero-valent copper nanoparticles with high purity were obtained by thismethod and there was no peak related to the oxidizedimpurities such as CuO and Cu$_2$O in the XRD and UV–Vis studies, both in the presence and in the absence of stabilizer. Onthe other hand, by this method, zero-valent copper nanoparticles were obtained in the absence of any anti-oxidant agent andany inert gas flow. The effects of synthesis parameters including initial concentration of precursor, polymer concentrationand the reaction temperature on the size and size distribution of copper nanoparticles were investigated using the UV–Visanalysis to determine the optimum synthesis conditions.

• Effect of the method for producing Cu–Cr$_3$C$_2$ bulk composites on the structure and properties

Copper–chromium carbide composites containing a carbide phase of 20–30 vol% were obtained with the use ofsolid- and liquid-phase mechanosyntheses, followed by magnetic pulse compaction (MPC) and spark plasma sintering. Themorphology, structural-phase composition, density, hardness and electrical conductivity of the composites were investigated.The structure of composites obtained by MPC represents regions of copper matrix hardened by superfine carbide precipitatessurrounded by a layer of chromium carbide. In the composites obtained by spark plasma sintering, the copper matrix hardenedby superfine carbide precipitates was divided into areas surrounded by a copper–chromium layer. A composite obtained bythe MPC of the powders synthesized using solid-phase mechano synthesis (MS) (copper, chromium and graphite) had thehighest values of Vickers microhardness (4.6 GPa) and Rockwell hardness (HRA 69). The best value of electrical conductivity(36% IACS) was achieved using liquid-phase MS (copper, chromium and xylene) and spark plasma sintering. Liquid-phaseMS is the only way to synthesize the powder with a small amount of the carbide phase and without contamination.

• Ultra-low friction and excellent elastic recovery of fullerene-like hydrogenated carbon film based on multilayer design

Multilayer fullerene-like hydrogenated carbon (FL-C:H) films were synthesized by using the chemical vapourdeposition technique with a different flow rate of methane. The typical fullerene-like structure of as-prepared films wasinvestigated by using transmission electron microscopy and Raman spectra. The prepared multilayered FL-C:H films showeda high elastic recovery ($\sim$90%), ultra-low friction coefficient ($\sim$0.019) and low wear rate ($\sim 3.0 \times 10^{−9}$ mm$^3$ Nm$^{−1}$) in humid air.

• Investigation of capacitance characteristics in metal/high-$k$ semiconductor devices at different parameters and with and without interface state density (traps)

Capacitance vs. voltage ($C−V$) curves at AC high frequency of a metal–insulator–semiconductor (MIS) capacitorare investigated in this paper. Bi-dimensional simulations with Silvaco TCAD were carried out to study the effect ofoxide thickness, the surface of the structure, frequency, temperature and fixed charge in the oxide on the $C−V$ curves. We evaluate also the analysis of MIS capacitor structures by different substrate doping concentrations with and without interfacestate density at different temperatures (100, 300 and 600 K). These studies indicate that the doping substrate concentrationand the traps enormously affect the high-frequency $C−V$ curve behaviour. We also demonstrate that for low and hightemperatures, the high-frequency $C−V$ curves behaviour changes, indicating that the capacitance due to the substrate issignificantly influenced in these conditions (bias and substrate doping concentration).

• Mathematical model of Boltzmann’s sigmoidal equation applicable to the set-up of the RF-magnetron co-sputtering in thin films deposition of Ba$_x$Sr$_{1−x}$TiO$_3$

In this work, we present the stoichiometric behaviour of Ba$^{2+}$ and Sr$^{2+}$ when they are deposited to make asolid solution of barium strontium titanate. Bax Sr$_{1−x}$ TiO$_3$ (BST) thin films of nanometric order on a quartz substrate were obtained by means of in-situ RF-magnetron co-sputtering at 495$^{\circ}$C temperature, applying a total power of 120 W divided into intervals of 15 W that was distributed between two magnetron sputtering cathodes containing targets of BaTiO$_3$ and SrTiO$_3$, as follows: 0–120, 15–105, 30–90, 45–75, 60–60, 75–45, 90–30, 105–15 and 120–0 W. Boltzmann’s sigmoidalmodified equation (Boltzmann’s profile) is proposed to explain the behaviour and the deposition ratio Ba/Sr of the BSTas a function of the RF-magnetron power. The Boltzmann’s profile proposal shows concordance with experimental data ofdeposits of BST on substrates of nichrome under the same experimental conditions, showing differences in the ratio Ba/Srof the BST due to the influence of the substrate.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 5
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019