Pulsed laser deposited ZnO:In as transparent conducting oxide

Zinc oxide (ZnO) and indium doped ZnO (IZO) thin films with different indium compositions were grown by pulsed laser deposition technique on corning glass substrate. The effect of indium concentration on the structural, morphological, optical and electrical properties of the film was studied. The films were oriented along c-direction with wurtzite structure and highly transparent with an average transmittance of more than 80% in the visible wavelength region. The energy band gap was found to decrease with increasing indium concentration. High transparency makes the films useful as optical windows while the high band gap values support the idea that the film could be a good candidate for optoelectronic devices. The value of resistivity observed to decrease initially with doping concentration and subsequently increases. IZO with 1% of indium showed the lowest resistivity of 2.41 x 10(-2) Omega cm and large transmittance in the visible wavelength region. Especially 1% IZO thin film was observed to be a suitable transparent conducting oxide material to potentially replace indium tin oxide. (C) 2011 Elsevier B.V. All rights reserved.

Quantum corrections to the conductivity in a perovskite oxide: A low-temperature study of LaNi1-xCoxO3 (0?x?0.75)

In this paper we propose to study the evolution of the quantum corrections to the conductivity in an oxide system as we approach the metal-insulator (M-I) transition from the metallic side. We report here the measurement of the low-temperature (0.1 Koxide system LaNi1-x CoxO3 (0?x?0.75). LaNiO3 is a metal and LaCoO3 is an insulator. The system is metallic for x?0.65. For all x, at low temperatures, the conductivity (?) rises with temperature (T). Below 2 K, ? follows a power-law behavior, ?(T)=?(0)+?Tm. For samples in the metallic regime, away from the metal-insulator transition (x?0.4), m?0.3�0.4. As the transition is approached [i.e., ?(0)?0], m increases rapidly; and at the transition [?(0)=0, xc?0.65], m?1. On the insulating side (x>0.65), m takes on large values and ?(0)=0. We explain the temperature dependence of ?(T), for T<2 K, on the metallic side (x?0.4), as arising predominantly from electron-electron interactions, taking into account the diffusion-channel contribution (which gives m=0.5) as well as the Cooper-channel contribution. In this regime, the correction to conductivity, ??(T), is a small fraction of ?(T). However, as the M-I transition is approached (x?xc), ??(T) starts to dominate ?(T) and the above theories fail to explain the observed ?(T).

Thermo and photoluminescence properties of Eu3+ activated hexagonal, monoclinic and cubic gadolinium oxide nanorods

Different phases of Eu3+ activated gadolinium oxide (Gd (OH)(3), GdOOH and Gd2O3) nanorods have been prepared by the hydrothermal method with and without cityl trimethyl ammonium bromide (GAB) surfactant. Cubic Gd2O3:Eu (8 mol%) red phosphor has been prepared by the dehydration of corresponding hydroxide Gd(OH)(3):Eu after calcinations at 350 and 600 degrees C for 3 h, respectively. When Eu3+ ions were introduced into Gd(OH)(3), lattice sites which replace the original Gd3+ ions, a strong red emission centered at 613 nm has been observed upon UV illumination, due to the intrinsic Eu3+ transition between D-5(0) and F-7 configurations. Thermoluminescence glow curves of Gd (OH)(3): Eu and Gd2O3:Eu phosphors have been recorded by irradiating with gamma source ((CO)-C-60) in the dose range 10-60 Gy at a heating rate of 6.7 degrees C sec(-1). Well resolved glow peaks in the range 42-45, 67-76,95-103 and 102-125 degrees C were observed. When gamma-irradiation dose increased to 40 Gy, the glow peaks were reduced and with increase in gamma-dose (50 and 60 Gy) results the shift in first two glow peak temperatures at about 20 degrees C and a new shouldered peak at 86 degrees C was observed. It is observed that there is a shift in glow peak temperatures and variation in intensity, which is mainly attributed to different phases of gadolinium oxide. The trapping parameters namely activation energy (E), order of kinetics (b) and frequency factor were calculated using peak shape and the results are discussed. (C) 2010 Elsevier B.V. All rights reserved.

Retarding effect of surface hydroxylation on titanium(IV) oxide photocatalyst in the degradation of phenol

Nanosized powders of TiO2 (anatase) were prepared by the hydrothermal method, acid-medium hydrolysis or by vacuum freeze-drying of sols, and annealing at temperatures <700-degrees-C. Photocatalytic activities of these powders in the mineralization of phenol, were evaluated in comparison to that of Degussa P25. Kinetic data indicated that surface hydroxylation had a retarding effect on the degradation of phenol. Formation of stable peroxotitanium species were observed on hydroxylated powders, whereas only V(Ti)-O- hole trap centres were detected by EPR on the heat treated samples. The data supports direct hole oxidation of the substrate preadsorbed on the photocatalyst, which is otherwise blocked by surface hydroxyls.

Solid Oxide-Ion Electrolytes

Solid oxide-ion electrolytes find application in oxygen sensors, oxygen pumps and in high-temperature electrolyser-fuel-cell hybrid systems. All the solid electrolytes known so Qr, however, exhibit: tow oxide-ion conductivities below 973 K. Therefore, there is a need for fast oxide-ion conductors operative at temperatures around 673 K, Recently, efforts have been directed towards developing such materials. This article summarizes various type of oxide-ton electrolytes reported in literature and outlines a strategy for the identificatiom/synthesis of improved materials.

Universal Stability and Temperature Dependent Phase Transformation in Group VIIIB-IB Transition Metal FCC Nanowires

Atomistic simulation of Ag, Al, Au, Cu, Ni, Pd, and Pt FCC metallic nanowires show a universal FCC -> HCP phase transformation below a critical cross-sectional size, which is reported for the first time in this paper. The newly observed HCP structure is also confirmed from previous experimental results. Above the critical cross-sectional size, initial < 100 >/{100} FCC metallic nanowires are found to be metastable. External thermal heating shows the transformation of metastable < 100 >/{100} FCC nanowires into < 110 >/{111} stable configuration. Size dependent metastability/instability is also correlated with initial residual stresses of the nanowire by use of molecular static simulation using the conjugant gradient method at a temperature of 0 K. It is found that a smaller cross-sectional dimension of an initial FCC nanowire shows instability due to higher initial residual stresses, and the nanowire is transformed into the novel HCP structure. The initial residual stress shows reduction with an increase in the cross-sectional size of the nanowires. A size dependent critical temperature is also reported for metastable FCC nanowires using molecular dynamic, to capture the < 110 >/{111} to < 100 >/{100} shape memory and pseudoelasticity.

Interaction of Bacillus polymyxa with some oxide minerals with reference to mineral beneficiation and environmental control

Interaction of Bacillus polymyxa with calcite, hematite, corundum and quartz resulted in significant surface chemical changes not only of the cells but also in the minerals. Both the cell surfaces as well as quartz particles were rendered more hydrophobic after mutual interaction, whilst the rest of the minerals exhibited enhanced hydrophilicity after interaction with the bacteria. The bacteria were also observed to be capable of dissolving calcite, hematite and corundum and biosorbing the dissolved metal ions to varying extents. An excess of polysaccharides could be observed on biotreated calcite, hematite and corundum while the predominance of a protein-based metabolic product was evident on quartz surfaces. The utility of bioprocessing in the beneficiation of the above minerals through bioflotation and bioflocculation is demonstrated. (C) 1997 Elsevier Science Ltd.

Oxide nanotubes prepared using carbon nanotubes as templates

Hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis.

Role of silver doping in oxygen incorporation of oxide thin film

A distinctive characteristic of silver in oxygen incorporation of oxide thin films during pulsed laser ablation has been discovered. Optical emission spectroscopy studies of laser-induced plume of Ag-target indicates the presence of AgO species whose concentration increases with an increase in oxygen partial pressure. The formation of AgO in laser-plume has been found to be very useful for the realization of high temperature superconducting YBa2Cu3O7-delta (YBCO) and giant magnetoresistive La0.7MnO3-delta (LMO) thin films with dramatically superior quality if the target materials contained a small amount of silver. The improvement in the quality of these films is brought about by the supply of atomic oxygen to oxide lattices during their formation. This becomes possible due to the fact that Ag, after it is ablated with other constituent materials in the target, gets moderately oxidized in an oxygen atmosphere and the oxidized species dissociate back into Ag and nascent O at the substrate surface. The nascent oxygen is very highly reactive and is easily assimilated into the lattice of these compounds. (C) 1997 Elsevier Science S.A.

Surface modification and biobeneficiation of some oxide minerals using Bacillus polymyxa

The interaction of Bacillus polymyxa and minerals such as hematite, corundum and quartz resulted in significant surface chemical changes, both on the cell surfaces and on the interacted oxide minerals. After such treatment, quartz was rendered relatively more hydrophobic, while hematite and corundum were rendered more hydrophilic. Biopretreatment was observed to be beneficial in the separation of silica from hematite and alumina by both selective flocculation and flotation. The possible role of bacterial adhesion and metabilites in the biobeneficiation process is illustrated.

The effect of aluminosilicate on the delayed onset of upturn voltages of zinc oxide varistor ceramics

The effect of aluminosilicate (Al2SiO5) on the upturn characteristics of ZnO varistor ceramics has been investigated. Addition of Al2SiO5 shifts the point of upturn above 10(4) A cm(-2). The extended nonlinearity in the high current density region is better correlatable to the presence of higher density of trap stales and changing pattern of trap depths at the grain boundary interface as much as the grain interior conductivity. Microstructure studies show the formation and involvement of a liquid phase during sintering. The secondary phases, predominantly are antimony spinel, Zn7Sb2O12, zinc silicate, Zn2SiO4 and magnesium aluminium silicate. MgAl2Si3O10. Energy dispersive X-ray analyses (EDAX) show that Al and Si are distributed more in the grain boundaries and within the secondary phases than in the grain interiors. Capacitance-voltage analyses and dielectric dispersion studies indicate the presence of negative capacitance and associated resonance, indicative of the oscillatory charge redistribution involving increased trapping at the interface states. The admittance spectroscopy data show that the type of trap slates remains unaltered whereas the addition of Al2SiO5 increases the density of low energy traps. (C) 1997 Published by Elsevier Science S.A.

Magnetoresistance of the metallic perovskite oxide LaNiO3-delta

We report a study of the magnetoresistance (MR) of the metallic perovskite oxide LaNiO3-delta as a function of the oxygen stoichiometry delta (delta less than or equal to 0.14), magnetic field (H less than or equal to 6 T) and temperature (1.5 K less than or equal to T less than or equal to 25 K). We find a strong dependence of the nature of the MR on the oxygen stoichiometry. The MR at low temperatures changes from positive to negative as the sample becomes more oxygen deficient (i.e. delta increases). Some of the samples, which are more resistive, show resistivity minima at T-min approximate to 20 K. We find that in these samples the MR is positive for T > T-min and negative for T < T-min. We conclude that in the absence of strong magnetic interaction, the negative MR in these oxides can arise from weak-localization effects.

Microwave preparation of oxide bronzes

Several vanadium, tungsten, and molybdenum oxide bronzes have been prepared using microwave irradiation. Metal oxides and alkali metal iodides were used as starting materials, Intermittent grinding and inert atmosphere were found to be necessary for the synthesis of most of the bronzes, The reaction temperatures are remarkably lower than those employed for conventional synthetic techniques and the microwave assisted reactions proceed at extremely fast rates. The microwave synthesized bronzes consist of particles having long, rectangular rod-like morphology. (C) 1999 Academic Press.

Process-kinetics in facing targets sputtering of multi-component oxide thin films

The kinetics of the processes in facing targets sputtering of multicomponent oxide films is presented. The novel configuration of the process exhibits an enhanced ionization efficiency. Discharge diagnostics performed using optical emission spectroscopy revealed strong dependence of plasma parameters on process conditions. Numerical simulation based on thermalization and diffusion of sputtered atoms has been performed to estimate the transport efficiency in off-axis mode. Composition, structure and epitaxial quality of YBa2Cu3O7-x films prepared was found to be strongly dependent on atomic flux ratios (of Cu/Y and Ba/Y) arriving at the substrate, resputtering effect and phase stability of YBa2Cu3O7-x These studies have been shown to be useful in understanding the complex processes that occur in sputtering of multicomponent films. (C) 1999 Elsevier Science S.A. All rights reserved.