Sharif Digital Repository

Electrical conductivities in dark and light were investigated in Calcium doped Bismuth Ferrite thin films. Higher dark conductivity, in the order of 10 times higher than conductivity of bismuth ferrite, was observed for Bi 0.85Ca0.15FeO3 - δ. Structural analyses using Rietveld refinement showed a deviation from volume reduction for Bi 0.85Ca0.15FeO3 - δ which could be the reason of abnormally high conductivity for this compound. Although higher calcium doping reduced conductivity, photoconductivity was observed again. Atomic Force Microscopy investigations showed that surface roughness and grain size decreased with increasing calcium concentration. Enhanced photoconductivity is reported for... 

In this study, titania-ceria-graphene quantum dot (TC-GQD) nanocomposite was synthesized by hydrothermal method for the first time. The prepared nanomaterials were characterized by XRD, FTIR dynamic light scattering (DLS), FESEM, HRTEM, and EDX spectroscopy along with elemental mapping. The synergistic effect of the nanocomposite components was studied by diffuse reflectance spectroscopy (DRS) and electrical conductivity meter. The results showed that band gap of TC-GQD nanocomposite was shifted to visible lights relative to its components (1.3 eV), and electrical conductivity of the sample was significant increased to 89.5 μS cm−1. After chemical and physical characterization, prepared new... 

Device-to-device (D2D) communication improves spectrum efficiency (SE) and increases system capacity. Heterogeneous networks comprise macrocell and several small cells, such as picocells and femtocells, where femtocells are more efficient. In cooperative communications, one or several additional nodes help to send data from source to destination to improve the quality of service (QoS). Network coding (NC) in cooperative networks can extend data rate and coverage area of D2D communication. The purpose of this article is to minimize power consumption of transmitting nodes during network-coded cooperative D2D transmission to reduce the interference on co-channel transmissions. In this study, we... 

The effects of graphite content on the density and oxidation behavior of MgO-C refractory samples were studied. The samples were formulated with various amounts of graphite and their oxidation behavior was investigated (in an isothermal condition); using a Thermo Gravimetric system (TG), in air and at temperatures ranging from 900"C to 1450"C. The preliminary results showed that the porosity and density of tempered samples were decreased when the graphite content was increased. However, after heating the samples at higher temperatures, the decreasing rate of porosity was lowered. At the beginning of the oxidation process, the rate of weight loss was high, but was gradually decreased when the... 

The morphological characteristics as well the optical properties of Ca-doped BiFeO3 films grown by pulsed-laser deposition technique have been investigated. AFM images revealed that calcium has a radical effect on the surface features of BiFeO3 films. By utilizing spectrophotometer, transmission behaviour of the films was investigated. Local IV characteristics of the films disclosed about three orders of magnitude enhancement concerning electrical conductivity through Ca doping. X-ray photoelectron spectroscopy results revealed that Ca can reduce the valence state of iron in the compound  

Solid oxide fuel cells (SOFCs) are rapidly becoming recognized as a new alternative to traditional energy conversion systems because of their high energy efficiency. From an ecological perspective, this environmentally friendly technology, which produces clean energy, is likely to be implemented more frequently in the future. However, the current SOFC technology still cannot meet the demands of commercial applications due to temperature constraints and high cost. To develop a marketable SOFC, suppliers have tended to reduce the operating temperatures by a few hundred degrees. The overall trend for SOFC materials is to reduce their service temperature of electrolyte. Meanwhile, it is... 

In this research, cold compaction behavior and pressureless sinterability of WC, WC-10%wtCu and WC-30%wtCu powders were investigated. WC and WC/Cu powders were milled in a planetary ball mill for 20h. The milled powders were cold compacted at 100, 200, 300 and 400 MPa pressures. The compressibility behavior of the powders was evaluated using the Heckel, Panelli-Ambrosio and Ge models. The results showed that the PanelliAmbrosio was the preferred equation for description the cold compaction behavior of the milled WC and WC-30%wtCu powders. Also, the most accurate model for describing the compressibility of WC-10%wtCu powders was the Heckel equation. The cold compacts were sintered at 1400oC.... 

Magnesia-dolomite refractories have advantages such as stability in the basic environments, clean steel production, high corrosion resistance, proper covering in the cement furnace, and low production costs. However, their application is restricted due to low hydration resistance. In this research, the effects of nano and micro alumina particles on the microstructure, sintering behavior, and properties of magnesia-dolomite refractories were studied. For this purpose, MgO-CaO refractories were formulated using dolomite and magnetite and 0, 2, 4, 6 and 8 wt percentage nano and micro alumina were added to the formulation. Phase and microstructure analysis of the samples were performed using... 

In the present paper, the effect of silicon carbide (SiC) fines was studied on the phase and microstructural properties of bauxite-based low-cement refractory castables (LCC) at different firing temperatures. XRD and SEM techniques were employed to evaluate phase and microstructure analysis, and physical/mechanical properties were measured according to standard methods. The results showed that the oxidation of SiC particles related to the oxygen partial pressure and active/passive oxidation behavior of SiC fines could markedly affect the microstructure and properties of bauxite-based LCC fired at high temperatures. Despite the negative influence of addition of SiC fines on cold mechanical... 

Nanocars have been proposed to transport nanomaterials on the surface. Study of the mechanism of the motion of nanocars has attracted a lot of interests due to the potential ability of these nano-vehicles in the construction of nanostructures with bottom-up approach. Using molecular dynamics simulations, we study the motion of two nano-vehicles named “Nanocar” and “Nanotruck” on hexagonal boron-nitride monolayer. The obtained results reveals that, boron-nitride is an appropriate option to obtain higher mobility of nanocars compared with metal substrates. Considering different temperatures reveals that nanocars start to move on the BN at 200 K, while long range motions are observed at 400 K... 

Titania nanoparticles with high photocatalytic activity were prepared from titanium alkoxide dissolved in alcohol and water under acidic conditions. The effects of the key parameters including (alkoxide/water) ratio, (alkoxide/alcohol) ratio, precursor type, solvent type, type and concentration of stabilizer, calcination temperature, presence of methylcellulose (MC) and hydrothermal treatment were studied. The optimal conditions were obtained through an experimental design technique. This technique is also used to find the main factors influencing the degradation of methylene blue (MB) and mass percent of anatase phase. The powders characteristics were investigated by XRD and... 

In this paper we have studied the motion of a nanocar and nanotruck on gold substrate using the classical molecular dynamics method. Analyzing the motion regime of the nanocar at different temperatures is one of the main goals of this paper. In the past years, similar molecules such as Trimmer, Z-car and nanotruck have been simulated by Konyukhov and Akimov. To increase the modeling accuracy in this paper we have used classical molecular dynamics contrary to previous works which used a rigid body molecular dynamics method. The result of our simulations were compared qualitatively to the experimental tests performed by Zhang et al. [12]. There was a good agreement between the results achieved... 

Embedded dielectric scatterers comprise an important approach for light trapping in dye-sensitized solar cells (DSCs) due to their simple fabrication process. The challenge in applying these scatterers lies in finding the optimal dimensions and concentration of the scatterers. This requires many experiments and it is often quite difficult to have a starting point for optimizing the concentration. Based on theories of light propagation in random media, we propose a simple model for DSCs with embedded silica spherical particles. Then, by full-wave optical calculations, we determine a narrow range for the concentration of silica particles that leads to the largest optical absorption in the... 

Spherical dielectric particles, nanofibers, and nanorods have been widely used as embedded scattering objects in nanostructured thin film solar cells. Here we propose micron-scale rod-like dielectric particles as a more effective alternative to the spherical ones for light trapping in thin film solar cells. The superior performance of these micro-rods is attributed to their larger scattering efficiency relative to the spherical particles as evidenced by full-wave optical calculations. Using a one-pot process, 1.7 μm-long bullet-shaped silica rods with 330 nm diameter are synthesized and their concentration in a N719-sensitized solar cell is optimized. A solar cell with an optimal... 

In this study, SnO 2-based varistors were prepared from mechanically activated nanocrystalline powders. Nanocrystalline powders were derived by subjecting the initial powders to intensive high-energy activation with different times and ball to powder ratio. The effect of activation parameters on the powder properties and sintering temperature, as well as microstructural, micro-electrical and macro-electrical properties of the final specimens was evaluated. Varistors derived from high-energy mechanical activation exhibit a higher density (98.3% relative density) and more refined microstructure upon sintering at 1,300 °C in comparison varistors prepared from conventional powders. Breakdown... 

In this study organically modified nanoclay were prepared by exchanging of the cetyltrimethylammonium (CTAB), with inorganic/metal ions/cations in montmorillonite structure. To investigate the influence of the amount of modifier on basal spacing and subsequent removal efficiency of hydrocarbon, different amount of modifier was used. The modified and unmodified nanoclays characterized by XRD, CHN and FTIR techniques. The X-ray diffraction results showed that the interlayer spacing of CTAB-modified clays increased from 12 to 22Å. The effectiveness of the sorbent materials for sorption of a range of products was investigated using crude oil, kerosene, gasoline and toluene. The process... 

Al2O3-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO2 and Y2O3 as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al2O3 and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl 3, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al2O3 hindered densification. In contrast, the addition of nano MgO and nano TiO2 to Al 2O3-5 vol.% SiC composites improved densification but Y2O3 did not have positive effect on... 

The objective of this study was to evaluate the effects of P 2O5 particle size distribution on the crystalline phases and microstructure of lithium disilicate glass-ceramics derived from the TiO2-ZrO2-Li2O-CaO-Al2O 3-SiO2 system for dentistry applications. The samples were made via fusion and casting procedure. Crystallisation as well as the morphology and microstructure of the samples were investigated using X-ray diffraction, differential scanning calorimetric and scanning electron microscopy. The results showed that the crystallisation of the samples occurred in the range of 500-650°C. The main crystalline phase was lithium disilicate (Li2Si2O5) along with Lithium metasilicate (Li2SiO3),... 

(Lanthanum, Cerium)(Iron, Manganese, Cobalt, Palladium)(Oxygen)3- Perovskite catalyst was prepared by the citrate route and deposited on ceramic monoliths via dip coating procedure. The catalyst was applied on a car with XU7 motors and the amount of emission was monitored with vehicle emission test systems in Sapco company. The results were compared with the imported catalyst with noble metals such as palladium, platinum and rhodium by Iran Khodro company based on the Euro III standards. The catalysts were characterized by specific surface area measurements, scanning electron microscopy, X-ray diffraction, line scan and map. In the results, obtained in the home made sample, the amount of...