Papers by Author: Ashari Maqsood

Abstract: One-dimensional CdZnS nanostructures have been synthesized through the sublimation. Effect of high substrate temperature on morphology, structural and optical properties of these nanostructures has been studied. X-Ray diffraction peak intensity, lattice parameters, crystallite size decreased with an increase in substrate temperature. The morphology changed with the increase in the substrate temperature. Raman Spectroscopy confirmed the existence of constituent elements in CdZnS solid solution and an increase of Zn concentration with the rise in substrate temperature. The nanostructures exhibited strong photoluminescence emission in the green light region with a substrate temperature-dependent blue shift of 53 meV in emission energy. The Stoke’s shift energy raised from 45 meV to 302 meV as the substrate temperature increased from 510 °C to 550 °C. The stoichiometric deviancies, crystallite size, and quantum confinement effects resulted into an increase in the optical band gap from 2.4 eV to 2.71 eV. The results showed that CdZnS nanostructures could be potential candidates for nanostructure based optoelectronics and photovoltaic devices.

Abstract: We measured the dc electrical resistivity as a function of temperature and dielectric parameters in the frequency range 100 Hz to 3 MHz of nanosized Zr-Mn spinel ferrites with nominal composition CoFe_2-2xZr_xMn_xO₄ (0.1 x 0.4). The dc electrical resistivity decreased with the rise in temperature for all the samples, showing a semiconductor like behavior. From the dc electrical resistivity the activation energy and drift mobility are determined. Both the drift mobility and activation energy increase with a rise in x. The dielectric constant, dielectric (losses) and ac electrical resistivity as a function of frequency are also reported. The low field ac magnetic susceptibility measurement showed that the ferrimagentic transition temperature is in the range of 4395 K to 6585 K.

Abstract: The first measurement of thermal transport properties on the polycrystalline D-Er₂Si₂O₇ have been made in the temperature range 77-300K. Both the thermal conductivity and the thermal diffusivity follow modified Euckens law in this temperature region. The Transient Plane Source technique (TPS) has been used to measure thermal conductivity and thermal diffusivity simultaneously.

Abstract: ZnO thin films were prepared by sol-gel method. Prepared thin films were then characterized by SEM, XRD, EDX and Hall effect measurements. SEM confirmed the morphological studies of ZnO thin films. Crystallite size is calculated using the Scherrer formula. Crystallite and grain sizes are obtained through XRD and SEM. EDS analysis confirms mass percentage of ZnO deposited. Decreasing trend of magneto resistance with temperature is observed. The optical transmission spectra of the solgel deposited ZnO thin films showed high transmittance (>70%) in the visible region and indicates that the transmittance of ZnO films gradually decreased as the thickness increased. Decreasing trend of resistivity and sheet resistance with thickness are also observed. The IV characterization of ZnO thin films under influence of UV and dark conditions are reported. The dc electrical resistivity data follow the hoping model.

Abstract: Samples of Cr doped cobalt ferrite were prepared by co-precipitation route. These particles were characterized by X-ray diffraction (XRD) at room temperature. The structural properties were observed before and after sintering. The FCC spinel structure was confirmed by XRD patterns of the samples. The crystallite sizes lie in the range of 37-60 nm. DC electrical properties as a function composition were measured. Scanning electron microscopy was used in order to investigate the surface morphology of the prepared samples. The system for thermoelectric power measurement was designed, developed and calibrated in the laboratory. The room temperature thermoelectric power was measured for the prepared samples. The magnitude of Seebeck coefficient depends on the composition and resistivity of the samples. The obtained values of Seebeck coefficient for CoFe₂O₄ are in good agreement to the reported values. Determined values of Seebeck coefficient for other studied compositions are an addition to the literature.

Abstract: Mn-Zn ferrite powders (Mn_0.5Zn_0.5Fe₂O₄) were prepared by the chemical co-precipitation method. The effect of sintering temperature on the crystalline phase formation and dielectric properties were investigated by X-ray diffraction and impedance analyzer respectively. The TGA/DTA analysis was carried out to know decomposition mechanism. Ferrites decomposed to Fe₃O₄ above 873 K sintering temperature. Crystallite size increased with increasing sintering temperature between 7-13 nm. The resistivity decreased with increase in temperature showing semiconducting like behaviour. Activation energy was in the range of 0.70 to 0.77eV for these samples. Dielectric constant decreased with increasing frequency. Relaxation peak occurred for loss tangent versus frequency curves. The ac conductivity explained using small polaron tunnelling (SPT) model.

Abstract: Spinel ferrites, which have the general chemical composition MeFe2O4, (Me = Co, Zn, Ni) are of interest due to their electronic, magnetic and optical properties. Nanosized Co-Zr-Mn spinel ferrites with nominal composition CoFe2-2xZrxMnxO4 (0.1≤ x≤0.4) have been prepared by the co-precipitation route. The products are characterized by X-ray diffraction, scanning electron microscopy (SEM) at room temperature, dc electrical resistivity as a function of temperature and dielectric parameters in the frequency range of 100 Hz to 3 MHz are also measured. The lattice constants agree with usual spinel ferrites. The particle size calculated from X-ray data by the Scherrer formula is in the range of 28-30 nm, while the average particle size varies from 15-25 nm obtained from the SEM measurements, X-ray density (Dx), Porosity (P) and bulk density (Dm) for all the samples are calculated. The dc electrical resistivity decreased with the rise in temperature for all the samples, showing a semiconductor like behavior. From the dc electrical resistivity the activation energy and drift mobility are determined. Both the drift mobility and activation energy increase with a rise in x. The dielectric constant, dielectric loss and ac electrical resistivity as a function of frequency are also reported. The low field ac magnetic susceptibility measurement showed that the ferrimagentic transition temperature is in the range of 439±5 K to 658±5 K.

Abstract: Mg-Co nano crystalline ferrites having general formula Mg1-xCoxFe2O4 (x=0, 0.05, 0.1, 0.15, 0.2, 0.25) were prepared by co-precipitation method. X-ray powder diffraction (XRD) patterns of the prepared samples show the formation single spinel phase. The crystallite size, lattice parameters and porosity of samples were calculated by XRD data analysis as function of cobalt concentration. The crystallite size for each sample was calculated using the Scherrer formula considering the most intense (3 1 1) peak lies in the range 27-35 nm. The lattice parameters increased with increase of cobalt concentration. It is because of the fact that cobalt has greater ionic radius then magnesium. The dielectric constant, dielectric loss tangent and ac electrical conductivity of the prepared samples is also measure. The observed variation in electrical and dielectric properties is explained on the basis of cations distribution among tetrahedral (A) and octahedral (B) sites. The variance in saturation magnetization, remanence magnetization and magnetic moment was also measured from BH curve of samples.