Formation of Zinc–Antimony-Based Spinel Phases

Formation of spinel phases in ZnO–Sb₂O₃and ZnO–Sb₂O₃–Bi₂O₃systems is studied by the use of X-ray diffraction. The formation of nonstoichiometric Zn_2.33Sb_0.67O₄phase is observed in both the systems at ∼900°C. However, in these systems, at higher temperatures ( T ≥ 1100°C), formation of the inverse spinel phase Zn₇Sb₂O₁₂is observed. The study has been extended to understand the effect of CrO₃doping on the stability of the different spinel phases in the previously mentioned systems. Interestingly, in both the systems, samples doped with CrO₃, displayed the presence of Zn_2.33Sb_0.67O₄phase <1200°C, indicating the stabilization of the spinel phase by CrO₃.     

Kinematic Design and Analysis of a 7 Degree-of-Freedom Dual-Stage Inspection Manipulator for Dexterous Subsea Applications

This paper describes the design of a 7 degree-of-freedom (d.o.f) manipulator for underwater inspection applications. The functional requirements of an underwater manipulator for subsea inspection are discussed and the desired performance requirements identified. The inspection process of a weld joint using a manipulator is described and the desirable attributes of a 5 d.o.f manipulator for the inspection process established. A novel kinematic structure, for Underwater Robotic Vehicle (URV) operation, having a 2 d.o.f launching stages and a 5 d.o.f inspection stage is proposed for the manipulator. This configuration increases the dexterity, without compromising on the total reach of the manipulator. The kinematic structure of the 7 d.o.f, 2 stage, manipulator is presented. A hybrid power actuation is proposed for the manipulator to exploit the benefits of both hydraulic as well as electric actuators. Kinematic analysis of the manipulator is presented. The link dimensions of the inspection stage manipulator is done on the basis of kinematic performance indices of the manipulator. The novel kinematic structure and the hybrid power actuation strategy results in a power efficient, dexterous manipulator for underwater applications.     

Stochastic inverse heat conduction using a spectral approach

An adjoint‐based functional optimization technique in conjunction with the spectral stochastic finite element method is proposed for the solution of an inverse heat conduction problem in the presence of uncertainties in material data, process conditions and measurement noise. The ill‐posed stochastic inverse problem is restated as a conditionally well‐posed L₂ optimization problem. The gradient of the objective function is obtained in a distributional sense by defining an appropriate stochastic adjoint field. The L₂ optimization problem is solved using a conjugate‐gradient approach. Accuracy and effectiveness of the proposed approach is appraised with the solution of several stochastic inverse heat conduction problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Magnetic Behaviour of Granular GdMnO<Subscript>3</Subscript> Film

The present study deals with the investigation of magnetic properties along with morphological and microstructure analyses of a multiferroic GdMnO₃ film fabricated on Si(100) substrate by the pulsed laser deposition technique. Rutherford backscattering spectroscopic analysis suggests that the film is fabricated in the form of diffused layers having different stoichiometric proportions. Raman spectroscopy signifies that few modes present in the film are associated with MnO₆ octahedra and some extra peaks indicating the mixed phase formation in tuning with the Rutherford backscattering spectroscopy. Atomic force microscopy confirms the granular nature of the film. Field-cooled and zero-field-cooled thermal magnetization curves show irreversible behaviour extending well above room temperature, which is associated with spin disorder. The presence of Gd⁺³ state and Mn⁺³/Mn⁺⁴ mixed states in the uppermost layers of the film was confirmed by near-edge X-ray absorption fine structure. Subsequently, in association with these observations, the film is a weak ferromagnetic at 5 K and even at room temperature.     

Effect of composition on steady state and transient photoconductivity in isocoordinated In<Subscript>x</Subscript>Sb<Subscript>30−x</Subscript>Se<Subscript>70</Subscript> (0 ≤ x ≤ 25) chalcogenide films

The study of steady state and transient photocurrent measurement provide important information about carrier generation and recombination phenomena in various semiconducting systems for photo-sensor device applications. In the present work, the composition dependent analysis of photocurrents was studied for thermally evaporated Se-rich In_xSb_30?xSe₇₀ films of average thickness 800 nm. The indirect optical gap has been calculated from the transmission and reflection data and the variation of molecular units was studied from the Raman spectroscopy. The initial rise of photocurrent sharply to approach a steady state value during illumination and fast decay to a constant persistent current after stopping the illumination has been observed. The intensity dependence of photocurrent obeys the power law I_Ph?=?F^γ, where the value of exponent tells about the recombination process. The decay of photocurrent has been fitted with stretched exponential function for different compositions and at different light intensities. These results are important for the development of low cost photo absorbers for solar cell applications and visible region responsive photo sensor devices.     

Optical,DC and AC electrical investigations of 4-hydroxy coumarin molecule as an organic Schottky diode

The current–voltage (I–V) and optical characteristics of 4-hydroxy coumarin Schottky diode were investigated. The conventional methods related with device were used to extract the various diode parameters. From dielectric study low dielectric constant and loss was observed. From its optical study, an indirect allowed transition is shown by this compound. The optical band gap (E _g ) was found to be around 3.78 eV. The observed properties shown by this molecule give a bright opportunity to explore its application for different organic devices.     

Effect of 80 MeV Au ions irradiation on CuInTe2 single crystals grown by CVT technique

Single crystals of CuInTe₂ (CIT) have been grown by the chemical vapor transport (CVT) technique using iodine as the transporting agent. CIT crystals were irradiated with 80 MeV Au⁸⁺ ions at room temperature at different fluences. The surface roughness was measured using an atomic force microscope (AFM). It was found to increase from 9.319 nm in the as-grown sample to 61.169 nm in the sample irradiated with a fluence of 1×10¹³ ions/cm². The intensities of the X-ray diffraction peaks corresponding to the (112) and (004/200) planes of the irradiated sample decrease with respect to the fluences. The full-width at half-maximum (FWHM) of X-ray rocking curves was measured as a function of different ion fluences. The FWHW increases with increase of ions fluences. This is attributed to the irradiation-induced partial amorphization of the top surface of the CIT crystals. The fall in absorption coefficients with photon energy is sharper for as-grown samples than irradiated samples. The band gap value gradually decreases from 1.04 to 0.977 eV upon Au⁸⁺ ions’ irradiation with a fluence of 1×10¹³ ions/cm². Photoluminescence (PL) measurements show a red shift compared to the as-grown CIT single crystals. The Raman modes of A₁ (high) and E and/or B₂ (LO) are observed at 123 and 173 cm⁻¹ in as-grown CIT single crystals, respectively. As the ion fluence is increased, the Raman frequency increases and the curves broaden. The above observed features are related to the large electronic energy transfer of the Au beam to the CIT crystals.     

Effect of 50 MeV Li ion irradiation on electrical, optical and mechanical properties of 4,4′-dimethylbenzophenone

4,4′-Dimethylbenzophenone (DMBP) single crystals were irradiated at room temperature and at liquid nitrogen temperature with 50 MeV Li³⁺ ions at fluences 1 × 10¹² and 1 × 10¹³ ions/cm². The dielectric constant and dielectric loss as a function of frequency of the applied ac field in the range from 20 Hz to 1 MHz and at temperatures ranging from 313 to 353 K were analyzed. The dielectric constant decreases with increase in frequency for all the temperatures. The dielectric constant and dielectric loss increase with fluence. Optical absorption was measured at different conditions. UV-Vis studies reveal the decrease in bandgap. The unirradiated as well as irradiated crystals were characterized by photoluminescence. Ion-induced changes were also studied with respect to their mechanical response using the Vicker’s microhardness technique and parameters including fracture toughness, brittleness index and yield strength are calculated.     

Studies on microstructure and density of sintered ZnO-based non-linear resistors

Systematic studies have been made of the grain growth and density of sintered ZnO-based systems containing one or more additive oxides of the type Nb₂O₅, Bi₂O₃, Sb₂O₃, CoO, Cr₂O₃, MnO₂, NiO and Al₂O₃. These samples were characterized using such techniques as scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The influence of the nature and amount of additive oxides and sintering temperature is discussed in relation to microstructure, density and the phases present.