Advanced Materials Research Vol. 678

Abstract: A Systematic investigation on structural, electrical, microstructure and compositions properties of La0.7Ba0.3MnO3 powder, prepared by a standard solid state reaction method, has been undertaken. The XRD pattern showed that the as prepared LBMO material was in single-phase rhombohedral structure. The electrical properties of as grown powders were carried out using standard four probe technique. The influence of dc biasing current on temperature dependence of resistance of La0.7Ba0.3MnO3 powder was reported. From electrical data it was observed that the electrical resistance decreased with bias current indicating the alignment of spins and increase in spin stiffness coefficient and decreasing the resistance at metal-insulator transition temperature (TMI). The surface morphology of the samples was studied by scanning electron microscope. From scanning electron micrographs, granular features were observed with average grain size of ~20nm.

Abstract: Nanocrystalline ZnS and Ni doped ZnS powders were synthesized by a simple chemical co-precipitation method at room temperature using sodium sulfide and acetates of Zinc and Nickel. 2-Mercapto ethanol is used as a capping agent. Structural and optical properties of as prepared samples were characterized using X-Ray diffraction (XRD), Scanning electron microscopy (SEM), Energy Dispersive Analysis using X-rays (EDAX) and Photoluminescence studies (PL). EDAX measurements confirmed the presence of Zn, Ni and S in the prepared samples. XRD analysis reveals that the Zn1-xNixS (x= 0.00 and 0.01) nanoparticles crystallized in zincblende structure. The average particle sizes of the nanoparticles are in the range of 2-3 nm. Shifting of photo luminescence peak to higher wavelength along with intensity quenching is observed for doped ZnS nanocrystals (NCs).

Abstract: Undoped and Cr doped ZnS nanoparticles with Cr concentrations of 3.0 at.% were prepared by a chemical co-precipitation method for the fist time, using 2-Mercaptoethanol as the capping agent and annealed the synthesized particles at 600°C for 3h in air. The effect of annealing on morphological, structural and optical properties of ZnS and ZnS:Cr have been studied and compared with as prepared samples. EDAX measurements confirmed the presence of Cr in the ZnS lattice and it also confirms the conversion of ZnS into ZnO after annealed at 600 0C/3h. Surface morphologies of all samples were characterized using scanning electron microscopy (SEM). XRD spectra of as synthesized nanoparticles of ZnS and ZnS:Cr exhibited cubic phase. After annealing, the cubic phase is transformed into hexagonal phase. The particle sizes of the ZnS:Cr powders were increased from 5 to 30 nm when the powders were annealed at 600°C. A stable blue emission peak at 445 nm is observed from the as prepared samples (pure ZnS and Cr doped ZnS) but annealed at 600 0C the PL peaked at 500 nm for pure ZnS and Cr doped ZnS nanoparticles exhibited PL peak at 500 nm as well as 654 nm. The emission intensity decreased in annealed particles compared to as synthesized samples.

Abstract: A simple room temperature ethanol assisted alcoholysis synthesis was adopted for the preparation of Sn doped indium oxide nanoparticles. Initially, pure indium oxide nanoparticles prepared using the method results in nanocubes, sized about 80 nm was identified using TEM analysis. When the dopant Sn was added at lower concentration the formed cubes were found to contain tiny particles inside nanocubes. As the concentration of Sn increases, it is observed that the particles were no more in cubical shape. For higher concentration of Sn, the formed particles were taken the shape of nanorods which are bunched together. This is one of the interesting results obtained for room temperature chemical synthesis. The concentration of the metal dopant was analyzed using XPS analysis and the obtained XRD pattern showed the dopant shift in 2θ. This work can be further extended to the field of gas sensors. Because, the metal oxide based gas sensors systems depends on the size and shape of the nanoparticles which can improve the sensing behavior of the material.

Abstract: The samples of Gd1-xPrxBa2Cu3O7-δ with compositions x = 0.0, 0.1 & 0.3 were prepared by ceramic route. The XRD study of all samples is carried out. The XRD studies of the samples prepared by ceramic route show GdPr-123 system have an orthorhombic pervoskite structure. The lattice parameters, oxygen content, volume of unit cell, orthorhombic distortion, hole concentration in CuO2 plane and charge on Cu-O plane were evaluated using XRD data. It is found that the lattice parameters, volume of unit cell increase while oxygen content orthorhombic distortion, hole concentration (Psh) and average charge (p) decrease as doping percentage of Pr increases. The resistivity measurement shows the transition temperature decreases while transition width increases with increasing Pr concentration. The suppression of superconductivity may be due to reduction in hole concentration or magnetic pair breaking. We report such qualitative results of Pr substituted Gd-123 in this paper quantitatively.

Abstract: Density functional theory is used to investigate the adsorption properties of O2, CO2, SO2 and NO2 gas molecules on pristine carbon nanotube (CNT) and Si-doped carbon nanotube (Si-CNT). All molecules except NO2 are physisorbed, with essentially no charge transfer between the CNT and molecules. The electronic properties of CNT are sensitive to the adsorption of NO2 because of its chemisorption, while they are insensitive to the O2, CO2 and SO2 molecules. The weak binding of these molecules on CNT is due to formation of charge-dipole interactions. In case of Si-CNT, all molecules are chemisorbed to the Si-C bonds with appreciable adsorption energy and significant charge transfer. The density of state analysis shows that the additional state near the Fermi level due to doping of silicon is responsible for chemisorption of the molecules. Further, our theoretical results suggest that molecule-induced modification of the density of states close to the Fermi level might significantly affect the transport properties of nanotubes.

Abstract: In this work, desorption of hydrogen from hydrogenated single walled carbon nanotubes (SWCNTs) functionalized with borane is discussed. A hydrogen storage medium based on SWCNTs functionalized with borane is designed. The SWCNTs are functionalized with borane (BH₃) using LiBH₄ as the precursor by solution cast method. The functionalized samples are hydrogenated. A storage capacity of 1.5 wt.% is obtained just above room temperature (50°C). The hydrogenated and dehydrogenated samples are characterized using FTIR and Raman studies. The thermogravimetry/differential thermal analysis (TG/DTA) results reveal that the entire amount of (1.5 wt.%) stored hydrogen is released in the temperature range 100 - 150°C. This temperature range is suitable for hydrogen fuel cells used for vehicular applications.

Abstract: Abstract. The effect of Au, Ag & Cu (1 wt%) photodeposition onto CdS nanorod (length ~ 116 nm, aspect ratio = 21, surface area = 81 m2/gm) has been studied by photocatalytic degradation of 0.5 mM salicylic acid both under direct sunlight and UV (125 W Hg arc lamp, 10.4 mW/cm²) irradiation. The bare CdS nanorod (NR) exhibited higher photoactivity as compared to low activity of bare CdS (~10 nm) nanosphere (NS) and Au & Ag photodeposition highly improved the CdS nanorod photoactivity compared with Cu deposition. The fluorescence emission of CdS nanorod at 479 nm is also quenched due to metals deposition. It is observed that Au-CdS (20 mg) nanorod composites completely degrade 0.5 mM (20 ml) salicylic acid within 2 h sun light exposure. The significant effect of Au-CdS photocatalytic activity on the various sizes (3.5 & 2 nm) of Au deposits has been observed during salicylic acid photodegradation.

Abstract: A novel and simple approach is reported to fabricate ZnO nanorods. Zinc acetate dihydrate, ethanol and de-ionized water were used to prepare seed layer. Zinc nitrate and hexamethylenetetramine solution were used for growth of ZnO nanorods. The ZnO nanorods were grown at two different temperatures of 90°C and 120°C and annealed at three different temperatures of 300°C, 400°C and 500°C in air atmosphere. Nanorod growth temperature and annealing temperature are varied and the corresponding changes in structural, morphological and optical properties were reported. The structure, orientation, surface morphology and optical properties of the ZnO nanorods were investigated by XRD, SEM & UV studies. The influence of growth and annealing temperatures on structural and optical properties were reported.

Abstract: Mass production of carbon nanofibers (CNFs) on a water soluble support has been achieved by chemical vapor deposition method. Carbon nanofibers have been synthesized using metal (Ni, Co, Fe) acetate as catalyst precursors at 680°C. Upon pyrolysis this catalyst yields metal nanoparticles directly. The sodium chloride was used as catalyst support, it was chosen because of its non toxic and water soluble nature. The problems such as detrimental effect, environment and even cost has been avoided by using water soluble support. The structure of the products was characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and X-ray diffraction method. The purity of as grown products and purified products was determined by thermal analysis. The yield of CNFs was up to 7500 wt% relative to the nickel catalyst have been achieved in the growth time of 15 mins. The advantage of this synthesis technique is the simplicity and use of easily available low cost precursors.