• Volume 39, Issue 5

September 2016,   pages  1363-1361

• Coating of titanium implants with boron nitride by RF-magnetron sputtering

Surface modification is necessary for titanium implants since it is unable to induce bone apposition. The beneficial effects of boron on bone formation, composition and physical properties make it suitable as a coating material. In the present study, surface properties of boron nitride (BN) coating on titanium implants were evaluated. Twenty-four implants and 12 abutments were coated with BN by RF-magnetron sputtering system. ATR–FTIR measurements were conducted to assess surface chemistry and morphology of BN-coated implants. Adhesion tests were performed by CSM nanoscratch test device to determine adhesion of BN to titanium surface. Surface profilometry and atomic force microscopy (AFM) was used to evaluate surface roughness.Mean roughness values were calculated. Contact angle measurements were done for evaluation of wettability. Surface characterization of coated implants was repeated after RF power of the system was increased and voltage values were changed to evaluate if these settings have an impact on coating quality. Three different voltage values were used for this purpose. Hexagonal-BN was determined in FTIR spectra. RF-coating technique provided adequate adherence of BN coatings to the titanium surface. A uniform BN coating layer was formed on the titanium implants with no deformation on the titanium surface. Similar roughness values were maintained after BN coating procedure. Before coating, the contact angles of the implants were in between 63$^{\circ}$ and 79$^{\circ}$, whereas BN coated implants’ contact angles ranged between 46$^{\circ}$ and 67$^{\circ}$. BN-coated implant surfaces still have hydrophilic characteristics. The change in voltage values seemed to affect the surface coating characteristics. Especially, the phase of the BN coating was different when different voltages were used. According to our results, BN coating can be sufficiently performed on pretreated implant surfaces and the characteristicsof BN coated surfaces can be changed with the change in parameters of RF-magnetron sputtering system.

• Electrical and magneto transport properties of La$_{0.8−x}$Ca$_x$Sr$_{0.1}$Ag$_{0.1}MnO$_3$($x = 0.1, 0.2, 0.3$) Lanthanum-based manganites La$_{0.8−x}$Ca$_x$Sr$_{0.1}$Ag$_{0.1}$MnO$_3$($x = 0.1, 0.2, 0.3$) doped with both alkaline metal (Ag) and alkaline earth (Ca and Sr) elements are studied. The structural characterization of polycrystalline samples synthesized through low temperature nitrate route confirms orthorhombic structure for all the investigated samples. The morphology of crystal grains shows that the grains are nearly uniform in size and spherical. Electrical resistivity of samples reveal two transition peaks typical of Ag-doped lanthanum-basedmanganites. Significant room temperature magneto resistivity (MR) is observed for all the samples. MR is found to behave almost linearly with temperature for$x = 0.1$sample for different magnetic field strengths in contrast to plateau type behaviour observed for$x = 0.3$sample. Standard temperature-dependent resistivity models such as small polaron and variable range hopping are used to fit the resistivity data in the high temperature range. In the low temperature domain, the resistivity data could be fitted to a model which combines electron–electron scattering and weak localization. • Synthesis, crystal structure, thermal analysis and dielectric properties of two mixed trichlorocadmiates (II) K$_{0.57}$(NH$_4$)$_{0.43}$CdCl$_3$and K$_{0.25}$(NH$_4$)$_{0.75}$CdCl$_3$are orthorhombic, space group Pnma,$Z = 4$, with$a = 8.8760(4)\AA$,$b = 3.9941(2)\AA$,$c = 14.7004(7)\AA$, and$Z = 4$,$a = 8.9567(9)\AA$,$b = 3.9957(4)\AA$,$c = 14.855(2)\AA$, respectively. Final R values are 0.01 and 0.02 for 608 and 834 reflections, respectively. In both the materials, the crystal structure has been determined by X-ray single crystal analysis at room temperature (293 K). The compound structures consist of K$^+$(or NH$^+_4$) cations and double chains of CdCl$_6$octahedra sharing one edge extending along$b$-axis. The mixture of KA$^+$/NH$^+_4$cations are located between the double chains ensuring the stability of the structure by ionic and hydrogen bonding contacts N/K–H$\ldots$Cl. Spectroscopic, dielectric and differential scanning calorimetry(DSC) measurements were performed to discuss the mechanism of the phase transition. These studies show that these materials, K$_{0.57}$(NH$_4$)$_{0.43}$CdCl$_3$and K$_{0.25}$(NH$_4$)$_{0.75}$CdCl$_3$, undergo a phase transition at 438 and 454 K, respectively. • Synthesis and luminescence properties of Tb$^{3+}-doped LiMgPO$_4$ phosphor

Polycrystalline sample LiMg$_{(1.x)}$PO$_4$:$x$Tb$^{3+}$ ($x = 0.001, 0.002, 0.005, 0.01, 0.02$) phosphor was synthesized via modified solid state method (MSSM). The prepared sample was characterized through XRD pattern (X-ray diffraction) and SEM (scanning electron microscope). Additionally, photoluminescence (PL), optically stimulated luminescence (OSL), thermoluminescence (TL) and other dosimetric properties including dose linearity, reusability and fading were studied. In OSL mode, sensitivity of prepared phosphor was found to be 2.7 times that of LiMgPO$_4$:Tb$^{3+}, B (BARC) phosphor and 4.3 times that of$\alpha$-Al$_2$O$_3$:C (BARC) phosphor. The TL glow consists of overlapping peaks in temperature range of 50-400$^{\circ}$C and first peak (P$_1$) was observed at 150$^{\circ}$C, second peak (P$_2$) at 238$^{\circ}$C, third peak (P$_3$) at 291$^{\circ}$C and fourth peak (P$_4$) at 356$^{\circ}$C. The TL sensitivity of second peak (P$_2$) of LiMgPO$_4$:Tb$^{3+}$phosphor was compared with$\alpha$-Al$_2$O$_3$:C (BARC) phosphor and found to be 100 times that of the$\alpha$-Al$_2$O$_3$:C (BARC) phosphor. The minimum detectable dose (MDD) was found to be 5.6$\mu$Gy. Moreover, photoionization cross-sections, linearity, reusability, fading and kinetic parameters were calculated. Also, photoluminescence spectra of LiMgPO$_4$:Tb$^{3+}$shows characteristic green.yellow emission exciting at 224nm UV source. • Synthesis and characterization of Eichhornia-mediated copper oxide nanoparticles and assessing their antifungal activity against plant pathogens In this paper, we report the biosynthesis and characterization of copper oxide nanoparticles from an aquatic noxious weed, Eichhornia crassipes by green chemistry approach. The aim of this work is to synthesize copper oxide nanoparticles by simple, cost-effective and ecofriendly method as an alternative to other available techniques. The synthesized copper oxide nanoparticles were characterized by UV–visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and Energy dispersive X-ray spectroscopy (EDX) analyses. The synthesized particles were highly stable, spherical in shape with an average diameter of$28\pm 4$nm. The synthesized nanoparticles were then explored to antifungal activity against plant pathogens. Highest zone of inhibition were observed in 100$\mu$g ml$^{−1}$of Eichhornia-mediated copper oxide nanoparticle against Fusarium culmorum and Aspergillus niger. This Eichhornia-mediated copper oxide nanoparticles wereproved to be good antifungal agents against plant fungal pathogens. • New NaSrPO$_4$:Sm$^{3+}$phosphor as orange-red emitting material Sm$^{3+}$-activated NaSrPO4 phosphors could be efficiently excited at 403 nm, and exhibited a bright red emission mainly including four wavelength peaks of 565, 600, 646 and 710 nm. The highest emission intensity was foundfor NaSr$_{1−x}$PO$_{4}$:$x$Sm$^{3+}$with a composition of$x = 0.007$. Concentration quenching was observed as the composition of$x$exceeds 0.007. The decay time values of NaSr1−xPO4:xSm3+ phosphors range from around 2.55 to 3.49 ms. NaSr$_{1−x}$PO$_{4}$:$x$Sm$^{3+}$phosphor shows a higher thermally stable luminescence and its thermal quenching temperature$T_{50}$was found to be 350$^{\circ}$C, which is higher than that of commercial YAG:Ce$^{3+}$phosphor and ZnS:(Al, Ag) phosphor. Because NaSr$_{1−x}$PO$_{4}$:$x$Sm$^{3+}$phosphor features a high colour-rendering index and chemical stability, it is potentially useful as a new scintillation material for white light-emitting diodes. • Synthesis and characterization of nanocomposites based on poly(3-hexylthiophene)-graft-carbon nanotubes with LiNi$_{0.5}$Mn$_{1.5}O$_4$ and its application as potential cathode materials for lithium-ion batteries

The P3HT grafted on CNTs to form the P3HT-$g$-CNTs nanocomposites was synthesized and their morphologies, structure have been characterized via the sedimentation test, scanning electron microscopy (SEM), X-raydiffraction (XRD) and transmission electron microscopy (TEM). The results showed that the P3HT-$g$-CNTs has a better thermal stability than that of the P3HT/CNTs blend. The nanocomposite based on P3HT-g-CNTs and doped spinel LiNi$_{0.5}$Mn$_{1.5}$O$_4$ (LNMO) have been fabricated via mixing process. The structure and morphologies of LNMO/P3HT-$g$-CNTs nanocomposites have also been performed by SEM, XRD and TEM. The electrochemical performance of LNMO/P3HT-$g$-CNTs nanocomposites as cathode materials of lithium-ion batteries were investigated by cyclic voltammetry and electrochemical impedance spectroscopy and exhibited the high diffusion of lithium ions in the charge–discharge process.

• Influence of pulse electrodeposition parameters on microhardness, grain size and surface morphology of Ni–Co/SiO$_2$ nanocomposite coating

Ni–Co/SiO$_2$ nanocomposite coatings and Ni–Co alloy coatings were prepared on steel substrate using direct and pulse electrodeposition methods. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-raymap and energy dispersive X-ray spectroscopy (EDX) were employed to investigate the phase structure, surface morphology, and elemental analysis of coatings, respectively. In high discharge rates, the surface morphology was rough, disordered and gross globular; on the contrary, in the low rates, it was smoother, more ordered and fine globular. Also, effect of electrodeposition parameters such as average current density, pulse frequency and duty cycle on the microhardness and grain size of nanocomposite coatings that produced through the pulse current electrodeposition method have been investigated. By amplifying both duty cycles up to 50% and average currentdensity from 2 to 6 A dm$^{−2}$, microhardness increased, while the grain size decreased. But when duty cycle mounted on more than 50% and the average current density went up to 8 A dm$^{−2}$, microhardness lessened, while the grain size rose. The optimum value for pulse frequency was about 25 Hz. Results showed that microhardness of nanocomposite coatings which were produced by pulse current method was higher than that of produced by direct currentmethod.

• Effect of strain rate on the fracture behaviour of epoxy–graphene nanocomposite

In this study, epoxy-based nanocomposite was fabricated by the addition of graphene nanosheet via a solution casting method. To investigate the effect of strain rate on tensile properties of epoxy, tensile tests were done on standard samples at different strain rates (0.05–1 min$^{−1}$). The role of strain rate and presence of graphene on fracture behaviour of epoxy were also studied by investigation of the fracture surfaces of some samples by scanningelectron microscopy (SEM). Finally, Eyring’s model was performed to clarify the role of strain rate on activation volume and activation enthalpy of epoxy. The results of tensile tests showed a maximum strength of epoxy–graphenenanocomposite at the graphene wt% of 0.1%. Tensile strength of epoxy obviously improved with increasing strain rate, but tensile strength of epoxy/graphene nanocomposite sample was less sensitive. Fracture micrographs showed that the mirror zone of the fracture surface of epoxy diminished by increasing strain rate or addition of graphene; and final fracture zone also became rougher. Finally, by investigation of the activation enthalpies, it was showed that much higher enthalpy was needed to fracture the nanocomposite sample, as the activation enthalpy changed from 41.54 for neat epoxy to 67.34 kJ mol$^{−1}$ for EP–0.1% GNS sample.

• Impact of lubrication on the tribological behaviour of PTFE composites for guide rings application

In this study, the friction and wear behaviours of polytetrafluoroethylene (PTFE)-based composites were comparatively evaluated under dry sliding and oil-lubricated conditions. Two PTFE composites filled with bronze and bronze $+$ molybdenum disulfide (MoS$_2$) were considered. These composites were used as guide rings for hydraulic actuating cylinder. Friction and wear tests of the composite specimens sliding against high chromium steel ball were conducted using reciprocating linear tribometer. The wear mechanisms of the composites under the two different sliding conditions were analysed and discussed based on scanning electron microscopic (SEM) examinationsof the worn surface and optical micrographs of the steel counterface. Under the oil-lubricated condition, the friction and wear behaviours of the composites were considerably improved if compared to that under the dry sliding. The oil adsorbed layer limited the transfer of the composite to the steel counterface and avoided the oxidation of the MoS$_2$ during the sliding test.

• In vitro bioactivity studies of larnite and larnite/chitin composites prepared from biowaste for biomedical applications

Larnite (Ca$_2$SiO$_4$) was synthesized by the sol–gel combustion process by using raw eggshell powder as a calcium source and urea as a fuel. The main focus of this work is to convert biowaste into a biomedical material ata low-processing temperature. X-ray diffraction (XRD) pattern confirms the phase purity of the larnite and Fourier transform infrared (FTIR) spectra confirms the presence of characteristic functional groups of larnite. Scanningelectron microscopy (SEM) image shows agglomerated particles with cauliflower-like morphology and energy dispersive X-ray spectroscopy (EDX) confirms the presence of the stoichiometric ratio of required elements. Atomicforcemicroscope (AFM) images reveal the presence of pores on the surface of spherical particles. Larnite/chitin composites were fabricated into scaffold with different ratios of bioceramic to biopolymer (70:30, 80:20) to investigatethe influence of the polymer content on the apatite formation ability in simulated body fluid (SBF) medium. XRDpattern and FTIR spectra of the scaffold immersed in SBF shows apatite deposition within 5 days. The deposition ofhydroxyapatite (HAP) on the scaffold surface increases with the increase in polymer content of the composite.

• Hybrid filler composition optimization for tensile strength of jute fibre-reinforced polymer composite

In present research work, pultrusion process is used to develop jute fibre-reinforced polyester (GFRP) composite and experiments have been performed on an indigenously developed pultrusion experimental setup. The developed composite consists of natural jute fibre as reinforcement and unsaturated polyester resin as matrix with hybrid filler containing bagasse fibre, carbon black and calcium carbonate (CaCO$_3$). The effect of weight content of bagasse fibre, carbon black and calcium carbonate on tensile strength of pultruded GFRP composite is evaluated and the optimum hybrid filler composition for maximizing the tensile strength is determined. Different compositions of hybrid filler are prepared by mixing three fillers using Taguchi L$_9$ orthogonal array. Fifteen percent of hybrid filler of different composition by weight was mixed in the unsaturated polyester resin matrix. Taguchi L$_9$ orthogonal array (OA) has been used to plan the experiments and ANOVA is used for analysing tensile strength. A regression model has also been proposed to evaluate the tensile strength of the composite within 7% error by varying the abovefillers weight. A confirmation experiment was performed which gives 73.14 MPa tensile strength of pultruded jute fibre polymer composite at the optimum composition of hybrid filler.

• Luminescence properties of ZnO/TiO$_2$ nanocomposite activated by Eu$^{3+}$ and their spectroscopic analysis

A new type of novel orange-red emitting Eu-doped ZnO/TiO$_2$ nanocomposite phosphors have been synthesized by simple low temperature co-precipitation route. Structure and morphology of the prepared sample havebeen investigated using X-ray diffraction and field emission scanning electron microscopy (FESEM) techniques. XRD pattern confirmed the presence of both phases of ZnO and TiO$_2$ simultaneously. The luminescence properties, such as photoluminescence (PL) excitation and emission spectra, Judd–Ofelt parameters, CIE colour coordinates and the dependence of luminescence intensity on the doping level were investigated. The luminescence spectrumcharacteristics of Eu$^{3+}$ ions have a strong dependence on Eu$^{3+}$ doping levels as well as ZnO/TiO$_2$ ratio variations. The photoluminescence results indicate that these phosphors could be efficiently excited by near-ultraviolet radiation, which causes emissions in orange–red regions.

• Effect of height to diameter ($h/d$) ratio on the deformation behaviour of Fe–Al$_2$O$_3$ metal matrix nanocomposites

The present paper reports the effect of height to diameter ($h/d$) ratio on the deformation behaviour of Fe–Al$_2$O$_3$ metal matrix nanocomposites (MMNCs) during bulk processing. Sintered compacts were machined to the required size with different $h/d$ ratios. Test specimens were subjected to deformation at room temperature under three different interfacial friction conditions such as dry, solid and liquid lubrications. Deformed specimensshow a significant improvement in the density and hardness. Results also revealed the formation of a nanosize iron aluminate phase due to reactive sintering, which in turn contributes to grain refinement. Experimental density of the specimens was also verified with the theoretical density using the standard equations. It is expected that the present work will be useful in designing and developing MMNC products with better quality at competitive cost.

• Tailoring ultrafine grained and dispersion-strengthened Ti$_2$AlC/TiAl composite via a new fabrication route

In situ Ti$_2$AlC/TiAl composite was fabricated by hot-pressing method via the reaction system of Ti$_3$AlC$_2$ and Ti-Al pre-alloyed powders at low temperature of 1150$^{\circ}$C. The composite mainly consisted of TiAl, Ti$_3$Al and Ti$_2$AlC phases. Fine Ti$_2$AlC particles were homogeneously distributed and dispersed in the matrix. Ti$_2$AlC played the significant role of deflecting and blunting the cracks and contributed to improve the mechanical properties of the composite. The Vickers hardness, flexural strength and fracture toughness were 6.2 GPa, $993.9\pm 50.8$ MPa and $6.7\pm 0.3$ MPa m$^{1/2}$, respectively.

• Microstructure and oxidation behaviour of TiAl(Nb)/Ti$_2$AlC composites fabricated by mechanical alloying and hot pressing

TiAl-based intermetallic matrix composites with dispersed Ti$_2$AlC particles and different amounts of Nb were successfully synthesized by mechanical alloying and hot pressing. The phase evolution of Ti–48 at%. Al elemental powder mixture milled for different times with hexane as a process control agent was investigated. It was found that after milling for 25 h, a Ti(Al) solid solution was formed; also with increase in the milling time to 50 h, an amorphous phase was detected. Formation of a supersaturated Ti(Al) solid solution after 75 h milling was achieved by crystallization of amorphous phase. Addition of Nb to system also exhibited a supersaturated Ti(Al,Nb) solid solution after milling for 75 h, implying that the Al and Nb elements were dissolved in the Ti lattice in a nonequilibrium state. Annealing of 75 h milled powders resulted in the formation of equilibrium TiAl intermetallic with Ti$_2$AlC phases that showed the carbon that originates from hexane, participated in the reaction to form Ti$_2$AlCduring heating. Consolidation of milled powder with different amounts of Nb was performed by hot pressing at 1000$^{\circ}$C for 1 h. Only the presence of $\gamma$-TiAl and Ti$_2$AlC was detected and no secondary phases were observed on the base of Nb. Displacement of $\gamma$-TiAl peaks with Nb addition implied that the Nb element was dissolved into TiAl matrix in the form of solid solution, causing the lattice tetragonality of TiAl to increase slightly. The values for density and porosity of samples indicated that condition of hot pressing process with temperature and pressure was adequate to consolidate almost fully densified samples. The isothermal oxidation test was carried out at 1000$^{\circ}$C in air to assess the effect of Nb addition on the oxidation behaviour of TiAl/Ti$_2$AlC composites. The oxidation resistance of composites was improved with the increase in the Nb content due to the suppression of TiO$_2$ growth, the formation and stabilization of nitride in the oxide scale and better scale spallation resistance.

• Development and evaluation of degradable hydroxyapatite/sodium silicate composite for low-dose drug delivery systems

This study was designed to develop innovative degradable hydroxyapatite (HAp)-based systems working as potential carriers for low-dose drugs. The HAp-based systems combine three components: HAp, sodium silicate and citric acid (HSC), which together could exhibit optimal characteristics as drug carriers. Both synthetic HAp (s-HAp) and extracted biological HAp (b-HAp) were used as sources of HAp due to their optimal biological properties and adsorption capacity. The s-HAp powder was prepared by co-precipitation method, while the b-HAp powder was extracted from bovine bone. Aqueous drug solutions of the atenolol, antihypertensive drug, were used as a model drug to investigate the drug release behaviour from HSC composites. The properties of s-HAP, b-HAp powders and HSC composite tablets were characterized by conventional methods. The results revealed that both s-HAp and b-HAp are pure powders and exhibited agglomerated microstructures with grain sizes less than 100 $\mu$m. The HSC composite tablets exhibited a dense structure, excellent compressive strength and excellent in-vitro release behaviour of atenolol. The results indicated that HAp powders and their composite tablets can be promised as economic raw materials and carriers for low-dose drugs.

• Structural, electrical and electrochemical studies of LiNi$_{0.4}M_{0.1}$Mn$_{1.5}$O$_4$ ($M$ = Co, Mg) solid solutions for lithium ion battery

The LiNi$_{0.4}M_{0.1}$Mn$_{1.5}$O$_4$ ($M$ = Co, Mg) solid solutions are synthesized by citric acid assisted sol–gel method and characterized by using TG/DTA, XRD, FTIR, EPR and SEM. The electrochemical characterization is carried out using CR-2032 coin type cell configuration. The cyclic voltammogram shows two pairs of redox current peaks, 4.35/3.80 V and 4.90/4.37 V vs. Li in a typical case of Co-doped sample, ascribed to two-step reversible intercalation of Li. A.c.-impedance (Nyquist plot) shows high frequency semicircle and a sloping line in the low frequency region. The semicircle is ascribed to Li-ion migration through interface from the surface layer of the particlesto electrolyte. The LiNi$_{0.4}Co_{0.1}$Mn$_{1.5}$O$_4$ shows reasonably good capacity retention in 20 cycles of galvanostatic charge/discharge cycling.

• Structure and properties of silver-doped calcium phosphate nanopowders

Stable and antimicrobial silver-doped calcium phosphate nanopowders were synthesized using sol–gel route by setting the atomic ratio of Ag/(Ag +Ca) at 3%and (Ca $+$ Ag)/P at 1.67. Prior to synthesis of nanopowders, influence of time of hydrolyzation on pH and density of precursors were comprehensively studied. Hydrolyzation time was found to have profound influence on pH of constituent precursors. Sufficient hydrolysis resulted in early maturation of sol. Scanning electron microscopy (SEM) showed the heterogeneous and agglomerated state of particles with average size of $3.9\pm 1.9$ $\mu$m. Energy dispersive X-ray spectroscopy (EDX) presented uniform distributionof O, Ag, Ca and P elements in nanopowder. Fourier transform infrared spectroscopy (FTIR) confirmed the formation of apatitic structure, whereas X-ray diffraction (XRD) revealed the multiphase constitution of nanopowdersprimarily composed of $\beta$-TCP, Ag and other hybrid phases. Crystallite size and lattice parameters of $\beta$-TCP and Ag phases were increased with the rise in calcination temperature. Thermogravimetric analysis (TGA) showed threeregions of weight change and indicated the high thermal stability of nanopowders. Disk diffusion method was used to test the antimicrobial resistance of nanopowders against Escherichia coli and Staphylococcus aureus bacterial strains. All nanopowders exhibited antimicrobial resistance against both E. coli and S. aureus bacteria.

• Effects of size on mass density and its influence on mechanical and thermal properties of ZrO$_2$ nanoparticles in different structures

This study investigates the effect of size on mass density and its subsequent influence on the other physical parameters of zirconia nanoparticles in the structural forms of cubic, tetragonal and monoclinic. The general equations for these calculations are established based on the variation of lattice parameter model and surface internal atoms ratio. The mass density of nanoparticles differs from the bulk value when particle size decreases. At a diameter of 4 nm, the mass density values of zirconia nanoparticles are 3.898, 3.626 and 3.488 g $\cdot$ cm$^{−3}$ compared to 6.25, 6.1 and 5.87 g $\cdot$ cm$^{−3}$ for bulk cubic, tetragonal and monoclinic forms, respectively. These results indicate thatthe variation in mass density is largely due to the differences on their boundaries and the variation in lattice parameters. The calculated results agree well with the available experimental data for the monoclinic form structure ofZrO$_2$ nanoparticles. The relationship between mass density and melting temperature; and Debye temperature and cohesive energy are proposed. All these parameters have the same nanosize dependence in this regard.

• Understanding the effect of $n$-type and $p$-type doping in the channel of graphene nanoribbon transistor

In this paper, device performance of graphene nanoribbon field effect transistor (GNRFET) with different doping concentrations in different parts of the channel is reported. The study is performed by using atomistic simulations based on self-consistent solution of Schrodinger’s and Poisson’s equation within the non-equilibrium Green’s function formalism. The transfer and output characteristics suggest that device performance with $n$-type doping in the channel is better with smaller supply voltage compared to higher supply voltage. On increasing the $n$-type doping concentration, we obtained better on-current and output characteristics in comparison with undoped and $p$-type doped channel GNRFET. Further, we introduced step-doping profile in the graphene nanoribbon (GNR) channel and found that the device gives better on-current and good saturation condition when compared to undoped or uniformly-doped channel.

• Structure and magnetic properties of Zr–Mn substituted strontium hexaferrite Sr(Zr,Mn)$_x$Fe$_{12−2x}$O$_{19}$ nanoparticles synthesized by sol–gel auto-combustion method

In this research, nano-sized powders of Zr–Mn substituted strontium hexaferrite (Sr(Zr,Mn)$_x$Fe$_{12−2x}$O$_{19}$ ($x = 0, 2, 2.5, 3$)) were synthesized by sol–gel auto-combustion route using subsequent heat treatment. The samples were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), Mössbauer spectroscopyand vibration sample magnetometer (VSM) techniques. XRD and Mössbauer spectroscopy results revealed formation of Sr(Zr,Mn)$_x$Fe$_{12−2x}$O$_{19}$ accompanied with Mn$_{\delta}$Fe$_{2−\delta}$O$_4$ lateral phase in the samples. Also, FTIR and XRDresults demonstrated presence of SrO impurity phase. FESEM micrographs show particle size reduction and presence of two distinct powder morphologies with different brightness levels with Zr$^{4+}$ and Mn$^{2+}$ substitutions which approves existence of lateral phases in the substituted samples. TEM micrographs show nanometric particles with sizes smaller than 100nm with high crystallinity. Mössbauer results showed that at low level of substitution, Zr$^{4+}$ ions prefer to occupy both 4f1 and 2b however, at higher level of substitution, they prefer exclusively 4f1 site. While, Mn$^{2+}$ ions distributed approximately equally between 12k and 2a sites. The presence of nonmagnetic Zr$^{4+}$ cation leads to decrease in exchange interaction, especially at 12k and 2a sites. VSM results showed decrement of coercivity force (${}_i$H$_c$) from 5593.60 to 3282.46 Oe and maximum magnetization from 62.60 to 46.15 emu g$^{−1}$, respectively, by increment of Zr–Mn substitution values. Variations in maximum magnetization magnitude have been explained on the basis of occupation of the substituted cations at different iron sites.

• Atomistic simulation of the structural and elastic properties of magnesite

Atomistic simulation was carried out to study the structural and elastic properties of MgCO$_3$ magnesite within the pressure range of the Earth’s mantle based on a novel force field. The lattice parameters and elasticconstants as a function of pressure up to 150 GPa are calculated. The results are in good agreement with the available experimental data and previous theoretical results, showing no phase transition over the pressure range of interest. We also found that magnesite exhibits a strong anisotropy throughout the lower mantle and that the nature of the anisotropy changes significantly with depth.

• Detection of anomalies in NLO sulphamic acid single crystals by ultrasonic and thermal studies

The ultrasonic pulse echo overlap technique (PEO) has been used to measure the velocities of 10 MHz acoustic waves in sulphamic acid single crystals in the range of 300–400 K. This study evaluated all the elastic stiffnessconstants, compliance constants and Poisson’s ratios of the crystal. The temperature variations of the elastic constants have been determined. The phase transition studies above room temperature were investigated using ultrasonic PEO technique. This study has suggested new weak elastic anomalies for the crystal around 330 K. The transverse elastic constants C44 and C66 have shown clear thermal hysteresis of 2 K. The present differential scanningcalorimetric (DSC) studies carried out at a slow heating rate have also suggested weak phase transition around 331 K. The present elastic and thermal studies have been substantiated by already reported DC electrical conductivitystudies around 330 K.

• Evidence for the complicated Fermi surface in 2H- and 4H-NbSe$_2$

In this study, we have found superconducting state (SC) at 7.4 and 6.4 K and charge density wave state (CDW) at 35 and 42 K in our 2H- and 4H-NbSe$_2$ single crystals, respectively. Besides this, there exists a positive magneto-resistance (MR) below the CDWtransition temperature on both the crystals. Therefore, we have calculated their fractional change in MR i.e., $\Delta \rho/\rho_0$ around 8 K in $H_{\perp}$ plane of NbSe$_2$ and $H_{\parallel}$ plane of NbSe$_2$ configurations. Both single crystals show anisotropic $\Delta \rho/\rho_0$, which are described by Kohler’s rule, two-band model and magnetic breakdown model. In the present scenario, the magnetic breakdown model explains our anisotropic $\Delta \rho/\rho_0$ better than other two models: Kohler’s and two-band model. This model also established the presence of complicated Fermi surface on both single crystals.

• Embedded atom approach for gold–silicon system from ab initio molecular dynamics simulations using the force matching method

In the present paper, an empirical embedded atom method (EAM) potential for gold–silicon (Au–Si) is developed by fitting to ab initio force (the ‘force matching’ method) and experimental data. The force database is generated within ab initio molecular dynamics (AIMD). The database includes liquid phase at various temperatures. Classical molecular dynamics simulations are performed to examine structural, coordination numbers, structure factors and dynamic properties of Au$_{81}$Si$_{19}$ alloy, with the interaction described via EAM model. The results are in good agreement with AIMD simulations and experimental data.

• Nanoscaled In$_2$O$_3$:Sn films as material for thermoelectric conversion: achievements and limitations

In this paper, thermoelectric properties of nanoscaled In$_2$O$_3$:Sn films are considered. The limitations that may appear during the usage of such materials in devices developed for the market of thermoelectric generatorsand refrigerators are also analysed. It is shown that nanoscaled In$_2$O$_3$:Sn is a promising material for thermoelectric applications. It is also established that insufficient thermal stability of nanostructured materials is themain limitation of these materials application in high-temperature thermoelectric converters. Optimization of grain boundary parameters and the usage of specific surrounding atmosphere can significantly improve the efficiency of thermoelectric conversion of nanostructured materials in the region of intermediate temperatures.

• Effect of nickel oxide substitution on bioactivity and mechanical properties of bioactive glass

A small amount of nickel oxide is doped in bioglass$^{\circledR}$ system and it is replaced by silica. The use of 45S5 glass composition is one such material able to bond strongly to bone within 42 days. The 45S5 bioglass$^{\circledR}$ system develops a hydroxyl carbonate apatite (HCA) layer, which is chemically and crystallographically similar to mineral phase of bone. But it has low fracture toughness and mechanical weakness due to an amorphous glass network andit is not compatible for load-bearing applications. In the present work, the effect of addition of nickel oxide that annualizes the improvement in its mechanical strength and bioactivity is studied. Bioactivity of base glass and doped glass samples were tested through their HCA abilities by immersing them in simulated body fluid (SBF) for different days. The formation of HCA was confirmed by FTIR spectroscopy and pH measurement. Densities and mechanical properties of samples were also increased considerably by increasing the concentration of nickel oxide.

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Posted on July 25, 2019