Magnetic Properties of Mechanically Alloyed Cobalt-Zinc Ferrite Nanoparticles

In this work, the physical and the magnetic properties of cobalt-zinc ferrite nanoparticles, synthesized via high-energy ball milling (HEBM), were examined. X-Ray diffraction (XRD), field emission scanning electron microscopy (FeSEM), and scanning transmission electron microscopy (STEM) were used to study changes of the powder structure and morphology analyses. Hysteresis and permeability measurement were carried out using a BH hysteresisgraph system and an impedance analyzer, respectively. The results suggested improved magnetic properties of Co_0.5Zn_0.5Fe₂O₄ with increasing sintering temperature from 950 °C up to 1200 °C. However, the variations of the magnetic responses were consistent with the varying volume concentration of the ferrite composites. Unlike the highly crystalline pure ferrite which showed magnetic resonance within the measured frequency, the crystallineamorphous composites showed no visible resonance peak. This proved that the resonance peak shifted to higher frequency as a result of the single domain spin behavior in the absence of domain walls movement.     

Magneto-resistance and Excess Conductivity Studies of Tl(Ba2−y Mg y )Ca 2 Cu 3 O 10−δ Samples

The flux pinning characteristics of T l(B a _2?y M g _y )C a ₂ C u ₃ O _10?δ(0.0≤y≤ 1.5) samples have been studied under the influence of various dc magnetic fields in the light of thermally activated flux flow model. It was observed form the magneto resistivity measurements that the activation energy U has been increased in the sample with Mg incorporation of y=0.5, however, it is decreased in the samples with higher Mg doping. This shows that lower Mg doping concentration promotes enhancement, whereas its higher concentration suppresses the flux pinning characteristics of Tl(Ba _2?yMg _y )Ca ₂Cu ₃ O _10?δ (0.0 ≤y≤1.5) samples. The excess conductivity analysis of Tl(Ba _2?yMg _y )Ca ₂Cu ₃ O _10?δ (0.0 ≤ y ≤ 1.5) samples has shown that the coherence length along the c-axis ξ _c(0), the interlayer coupling J, the phase relaxation time of the carriers τ _? , and the Fermi velocity v _F of the carriers are suppressed with Mg doping. However, the values of B _c0(T), B _c1(T), and J _c(0) are enhanced which complement the magnetoresistivity analysis. These results showed that the flux pinning characteristics are enhanced for lower doping concentration of Mg at the charge reservoir layer sites.     

Influence of sintering temperature on secondary phases formation and microwave dielectric properties of Ca2Ce2Ti5O16 ceramics

Ca₂Ce₂Ti₅O₁₆ dielectric ceramics prepared by conventional solid-state ceramic route was investigated. Phase composition and microwave dielectric properties were measured using XRD and Vector network analyzer, respectively. XRD analysis of the calcined and sintered samples revealed the formation of CeO₂ and another unidentified phase (that vanished at ? 1400 °C) as secondary phases along with the parent Ca₂Ce₂Ti₅O₁₆ phase. The amount of the parent Ca₂Ce₂Ti₅O₁₆ phase increased with increasing sintering temperature from 1350 °C to 1450 °C accompanied by a decrease in the apparent density. The density decreased but ? _r and Q _u f _o increased with sintering temperature. An ? _r ～ 81.5, Q _u f _o ～ 5915 GHz and τ _f ～ 219 GHz were achieved for the sample sintered at 1450 °C.     

反应硼化烧结WCoB基金属陶瓷的组织与性能

采用单质钨粉、钴粉和硼粉结合反应硼化烧结法制备了WCoB基金属陶瓷,研究了WCoB基金属陶瓷在烧结过程中的物相转变和尺寸变化,烧结温度对其力学性能和显微组织的影响。结果发现:随着烧结温度的升高,材料物相逐渐由单质相变为二元硼化物相和三元硼化物相,并且材料的尺寸先发生细微收缩,再在硼化反应过程中逐渐增加,最后在液相烧结过程中逐渐减小;随着烧结温度的升高,WCoB基金属陶瓷的抗弯强度和硬度先增加后减小,在1420℃达到最大,分别为1470 MPa和84.6HRA,显著提高了WCoB基金属陶瓷的抗弯强度。     

Low-energy proton-induced defects in n/p InGaP solar cells

The effects of low-energy proton-induced degradation of photovoltaic properties and generation of deep-level defects in n⁺/p InGaP solar cells have been investigated. Energy-dependent effects included decreased solar cell efficiency and increase the carrier removal rate with decreasing proton energy. The spectral response depicts that the degradation is more at longer wavelengths with the increase of proton fluence. A new majority (hole) trap HP1 has been observed in low-energy proton irradiated p-InGaP at 0.90±0.05 eV above the valence band for the first time. The carrier removal rates were found to be 61433 and 8640 cm⁻¹ for 100 and 380-keV proton irradiation, respectively.     

A wind map of Bangladesh

Utilization of wind energy in Bangladesh has been slow mainly due to lack of quality wind data. Recent measurements in some places have shown significant wind energy potentials in Bangladesh. In this paper, a wind map is presented which incorporates several microscale features, such as terrain roughness, elevation etc. with a mesoscale model. Several meso-maps were obtained from global databases and a suitable model was chosen and modified for a 30-m elevation. Ground data from various sources were collected and modified for height and land condition adjustments based on local knowledge and GIS information. It was found that, the generated wind map and the modified ground data resemble. Annual average wind speed at 30 m height along the coastal belt is above 5 m/s. Wind speed in northeastern parts is above 4.5 m/s while inland wind speed is around 3.5 m/s for most part of Bangladesh. Small-scale wind turbines could be installed and tested in locations such as St. Martins Island, Cox’s Bazar, Patenga, Bhola, Barguna, Dinajpur, Thakurgaon and Panchagar.     

Analysis for superior radiation resistance of InP-based solar cells

Better radiation resistance of InP-based solar cells such as InGaP and InGaAsP cells, and minority-carrier-injection-enhanced annealing phenomena of radiation-induced defects in those materials previously found by the authors has been analyzed by considering introduction rates and annealing behavior of radiation-induced defects in InP-related materials. Radiation resistance of InP-related materials is found to be explained by lower damage coefficients and band-gap energy effects on solar cell degradation compared to other materials.     

Growth and characterization of Ni:DLC composite films using pulsed laser deposition technique

The structure and surface morphology of Ni-incorporated diamond like carbon (Ni:DLC) films have been investigated. These films were deposited on Si substrates using pulsed laser deposition (PLD) technique. A KrF Excimer laser (λ = 248 nm) was used for co-ablation from multi component Ni–graphite target. The concentration of Ni was varied by ablating the Ni part of the target with various numbers of laser pulses. The SEM and AFM analysis reveals that the surface is composed of segregates of Ni which increases with the increase in Ni content during the growth process. The structural investigations by XRD and Raman spectroscopy provided information about the orientation of the incorporated constituent and the ordering of the carbon species. Maximum height of the nano structures which were observed on the surface was ∼50 nm. The G-peak of the graphite was shifted towards higher wave number due to enhancement in SP² sites which have been increased due to the increase in the Ni concentration. A small change in the surface roughness ranging from 7.78 nm to 13.1 nm due to increased Ni concentration was also observed.