Bashir Ahmmad

Room temperature dielectric and magnetic properties of Gd and Ti co-doped BiFeO3 ceramics

Room temperature dielectric and magnetic properties of BiFeO3 samples, co-doped with magnetic Gd and non-magnetic Ti in place of Bi and Fe, respectively, were reported. The nominal compositions of Bi0.9Gd0.1Fe1–xTixO3 (x = 0.00-0.25) ceramics were synthesized by conventional solid state reaction technique. X-ray diffraction patterns revealed that the substitution of Fe by Ti induces a phase transition from rhombohedral to orthorhombic at x > 0.20. Morphological studies demonstrated that the average grain size was reduced from ∼1.5 μm to ∼200 nm with the increase in Ti content. Due to Ti substitution, the dielectric constant was stable over a wide range of high frequencies (30 kHz to 20 MHz) by suppressing the dispersion at low frequencies. The dielectric properties of the compounds are associated with their improved morphologies and reduced leakage current densities probably due to the lower concentration of oxygen vacancies in the compositions. Magnetic properties of Bi0.9Gd0.1Fe1–xTixO3 (x = 0.00-0.25) ...

Anomalous coercivity enhancement with temperature and tunable exchange bias in Gd and Ti co-doped BiFeO3 multiferroics

We have investigated the effects of temperature on the magnetic properties of the Bi0.9Gd0.1Fe1−x Ti x O3 (x = 0.00–0.20) multiferroic system. Unexpectedly, the coercive fields (H c ) of this multiferroic system increased with increasing temperature. The coercive fields and remanent magnetization were higher over a wide range of temperatures in sample x = 0.10, i.e. in a sample with a composition Bi0.9Gd0.1Fe0.9Ti0.1O3 than those of x = 0.00 and 0.20 compositions. Therefore, we carried out temperature-dependent magnetization experiments extensively for sample x = 0.10. The magnetic hysteresis loops at different temperatures exhibit an asymmetric shift towards the magnetic field axes, which indicates the presence of an exchange bias effect in this material system. The hysteresis loops were also carried out at temperatures of 150 K and 250 K by cooling down the sample from 300 K in various cooling magnetic fields (). The exchange bias field () values increased with and decreased with temperature. The values were tunable by field cooling at temperatures of up to 250 K.

Tunable exchange bias effect in magnetic Bi0.9Gd0.1Fe0.9Ti0.1O3 nanoparticles at temperatures up to 250 K

The exchange bias (EB) effect has been observed in magnetic Bi0.9Gd0.1Fe0.9Ti0.1O3 nanoparticles. The influence of magnetic field cooling on the exchange bias effect has also been investigated. The magnitude of the exchange bias field (HEB) increases with the cooling magnetic field, showing that the strength of the exchange bias effect is tunable by the field cooling. The HEB values are also found to be dependent on the temperature. This magnetically tunable exchange bias obtained at temperatures up to 250 K in Bi0.9Gd0.1Fe0.9Ti0.1O3 nanoparticles may be worthwhile for potential applications.

Bioplastic based on starch and cellulose nanocrystals from rice straw

Bioplastic based on starch as the matrix and cellulose nanocrystals from rice straw as reinforcing filler were prepared in this study. The isolation of cellulose nanocrystal (CNC) followed a series of steps: delignification, sulfuric acid hydrolysis, and sonication. The process afforded short, rod-like CNCs with particle diameter ranging from 10 to 12 nm and crystallinity index of 76.1%. Fourier transform infrared analysis of the CNCs also confirmed absorption patterns typical of cellulose and the removal of silica. Bioplastic with different starch-to-CNC ratios were prepared by solution casting and evaporation method. Scanning electron micrographs of the films showed uniform dispersion of CNC in the starch matrix. Mechanical tests revealed that both tensile strength and modulus significantly increased with increasing CNC load while percent elongation decreased. The moisture uptake of the films reinforced with CNC also decreased an indication of improvement in water resistance. However, the thermal stability of the films decreased by the addition of CNC.

Size dependent magnetic and electrical properties of Ba-doped nanocrystalline BiFeO3

Improvement in magnetic and electrical properties of multiferroic BiFeO3 in conjunction with their dependence on particle size is crucial due to its potential applications in multifunctional miniaturized devices. In this investigation, we report a study on particle size dependent structural, magnetic and electrical properties of sol-gel derived Bi0.9Ba0.1FeO3 nanoparticles of different sizes ranging from ∼ 12 to 49 nm. The substitution of Bi by Ba significantly suppresses oxygen vacancies, reduces leakage current density and Fe2+ state. An improvement in both magnetic and electrical properties is observed for 10 % Ba-doped BiFeO3 nanoparticles compared to its undoped counterpart. The saturation magnetization of Bi0.9Ba0.1FeO3 nanoparticles increase with reducing particle size in contrast with a decreasing trend of ferroelectric polarization. Moreover, a first order metamagnetic transition is noticed for ∼ 49 nm Bi0.9Ba0.1FeO3 nanoparticles which disappeared with decreasing particle size. The observed stro...

Room temperature atomic layer deposition of TiO2 on gold nanoparticles

The authors developed a room temperature atomic layer deposition (ALD) system that can deposit TiO2 on gold nanoparticles by using tetrakis(dimethylamino)titanium and plasma-excited humidified argon. The growth per cycle of TiO2 was measured to be 0.25 nm/cycle on a monitored Si sample. For applying the nanoparticle coating, the source material, i.e., gold particles, is electrostatically attached to the susceptor in the ALD system to avoid their gas transport. These particles are then mixed by a rotating scraper during the ALD process. This system allows a conformal deposition of TiO2 without the aggregation of nanoparticles. The thickness of TiO2 for shell coating is controlled by counting the number of ALD cycles. The deposition of TiO2 coating with a nanometer scale thickness on the gold nanoparticle is demonstrated in this paper.

Dy doped BiFeO3: A bulk ceramic with improved multiferroic properties compared to nano counterparts

Abstract The synthesis as well as structural, multiferroic and optical characterization of Dy doped BiFeO3 multiferroic ceramic are presented. Bulk polycrystalline Bi 0.9 Dy 0.1 FeO 3 sample is synthesized by solid state reaction, while their nano counterparts are prepared using ultrasonic probe sonication technique. Significant improvement of phase purity in the as synthesized samples is observed after the doping of Dy both in bulk Bi 0.9 Dy 0.1 FeO 3 sample and corresponding nanoparticles as evidenced from Rietveld refinement. Magnetization measurements using SQUID magnetometer exhibit enhanced magnetic properties for Dy doped bulk Bi 0.9 Dy 0.1 FeO 3 ceramic compared to their nanostructured counterparts as well as undoped BiFeO3. Within the applied field range, saturation polarization is observed for Bi 0.9 Dy 0.1 FeO 3 bulk ceramic only. As a result, intrinsic ferroelectric behavior is obtained just for this sample. Optical bandgap measurements reveal lower bandgap for Dy doped bulk Bi 0.9 Dy 0.1 FeO 3 ceramic compared to that of corresponding nanoparticles and undoped BiFeO3. The outcome of this investigation demonstrates the potential of Dy as a doping element in BiFeO3 that provides a bulk ceramic material with improved multiferroic and optical properties compared to those of corresponding nanoparticles which involve rigorous synthesis procedure.

Large difference between the magnetic properties of Ba and Ti co-doped BiFeO3 bulk materials and their corresponding nanoparticles prepared by ultrasonication

The ceramic pellets of the nominal compositions Bi0.7Ba0.3Fe1−x Ti x O3 (x = 0.00–0.20) were prepared initially by standard solid state reaction technique. The pellets were then ground into micrometer-sized powders and mixed with isopropanol in an ultrasonic bath to prepare nanoparticles. The x-ray diffraction patterns demonstrate the presence of a significant number of impurity phases in bulk powder materials. Interestingly, these secondary phases were completely removed due to the sonication of these bulk powder materials for 60 minutes. The field and temperature dependent magnetization measurements exhibited significant difference between the magnetic properties of the bulk materials and their corresponding nanoparticles. We anticipate that the large difference in the magnetic behavior may be associated with the presence and absence of secondary impurity phases in the bulk materials and their corresponding nanoparticles, respectively. The leakage current density of the bulk materials was also found to suppress in the ultrasonically prepared nanoparticles compared to that of bulk counterparts.

Optimized design of moth eye antireflection structure for organic photovoltaics

To improve the power conversion efficacy of organic photovoltaics (OPVs), it is required to design antireflection structures that could realize efficient and broadband light trapping. In this article, we perform global optimization of the textured pattern of moth eye antireflection surfaces to maximize the short-circuit current density (JSC) of OPVs with a poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-based bulk heterojunction. We introduce an optimization algorithm consisting of two steps: in the first step, the simple grid search is conducted to roughly estimate a globally optimal solution, while in the second step, the Hooke and Jeeves pattern search is executed to refine the solution. By combining the optimization algorithm with the optical simulation based on the finite-difference time-domain method, we find the optimal period and height of moth eye array with which the level of JSC can be increased by 9.05% in the P3HT:PCBM-based organic solar cell. We also demonstrate that the optimized moth eye structure can significantly modify the light path at a long wavelength range to strengthen the electric field intensity and enhance energy absorption within the active layer.

Hybrid antireflection structure with moth eye and multilayer coating for organic photovoltaics

We propose a hybrid antireflection structure (ARS), which integrates moth eye texturing and multilayer interference coating, to improve efficiency of organic photovoltaic (OPV) solar cells. We perform nearly global optimization of the geometric parameters characterizing the hybrid ARS, by using optical simulations based on the finite-difference time-domain method. The proposed optimization algorithm consists of two steps: in the first step, only the moth eye structure is globally optimized and, in the second step, the whole hybrid structure is optimized efficiently based on the results of the first step. Thus, the optimal moth eye structure is additionally obtained as an intermediate result. By applying this optimization method to an organic thin film solar cell, we show that the short-circuit current density (JSC) is increased by 8.90% with the moth eye structure and by 9.89% with the hybrid ARS. We also study the sensitivity of photocurrent to the geometric parameters of hybrid ARS, and the change in the spatial distribution of electric field intensity by the ARS. The results show that the hybridization of the two types of light trapping techniques is effective to reduce the inhomogeneity in the electric field distribution and obtain higher electric intensity in almost the whole active layer. The design concept of the hybrid ARS is quite useful for improving light trapping in OPVs and allows for extending the options available for broadband antireflection.