Bulletin of Materials Science最新文献

The present work investigated the effect of Ni-doping on the structural and dielectric properties of Ni-doped zinc oxide (ZnO) prepared by a solvothermal route. The substitution of nickel at Zn sites was confirmed via X-ray diffraction and Rietveld refinement, which revealed a hexagonal crystal structure. Morphological characterization was performed with the help of SEM, in which a significant variation in morphology was observed with increasing nickel doping concentration. The dielectric properties of all the compositions were measured as a function of frequency (1 Hz–10 MHz) and temperature (100–350°C). A temperature-dependent dielectric study of the compositions showed negative values for the dielectric constant in the low-frequency and high-temperature regimes. A decrease in the dielectric constant is observed for ZnO ceramics with increasing nickel doping percentage and is explained with the Penn model. Finally, an attempt is made to discuss the possible mechanism for the emergence of a negative dielectric constant. Additionally, a detailed structural analysis was performed to understand the conductivity behaviour of the nickel-doped zinc oxide ceramics. For ZnO samples with higher nickel doping, epsilon-near-zero behaviour is achieved, which is necessary for developing waveguides and coil-free resonators.

In this work, a design for a broadband multi-resonator metamaterial absorber (MTMA) for satellite communications is proposed. This design is based on both numerical and experimental data. Four resonators were used to achieve a broad absorption of more than 99% in the frequency range of 12–16 GHz. The electromagnetic properties (absorption, reflection and transmittance) of the MTMA were analysed and extracted. The parametric effects including the type of substrate, its thickness and the change of the resonator width on the absorption spectrum were studied. Also, surface currents, electric field and magnetic field distributions were investigated and presented at 12.75 GHz. Besides, the proposed design was fabricated by using the LPKFan ProtoMat E33 machine and tested by waveguide connected to a vector network analyzer. It was found that there is a good agreement between the simulation and experimental results. The proposed design can be used for different applications, especially for the application of satellite communications.

Effect of dendritic and globular (rosette-like) morphology and its parameters on the hardness of Al–7.5% Si castings has been investigated. It was established that Brinell hardness demonstrates a slight increase with the rise of globules’ size and a slight decrease with the rise in dendrite parameter. In the first case, this is apparently due to isothermal holding in the process of obtaining castings, in the second case, with a decrease in the quenching rate of eutectics due to a decrease in the surface area of the dendrites because of coarsening.

Effective charge separation and use of hot charge carriers are considered to be the most essential factors affecting the activity of an excellent energy harvester. Herein, we have successfully decorated 3 nm of CdSe quantum dots (QDs) on the surface of reduced graphene oxide (rGO) using solvothermal method. Formation of CdSe–rGO nanocomposite (NC) has been confirmed by X-ray diffraction pattern, transmission electron microscopy and Raman analysis. Further, the emission spectrum of CdSe–rGO NC shows quenching of emission of CdSe QDs on the surface of rGO nanosheet. To elucidate this phenomenon, we have carried out time-correlated single-photon counting (TCSPC) measurements, which reveal efficient electron transfer, as the exciton lifetime of CdSe QDs in the NC is significantly reduced compared to bare CdSe QDs. Owing to the efficient electron transfer, this NC showed big boost in total shielding effectiveness (SE_T = 29 dB) when compared to graphene (SE_T = 23 dB) in electromagnetic interference shielding application.

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