Abstract: Manganese doped cobalt nano ferrites were synthesized by co-precipitation method having general formula Co1-xMnxFe2O4 (x =0.0-1.0). These materials are studied to analyze the structural effects on the associated materials properties. The prepared samples were heat treated at 7500 C for two hours. Sintering effect on the structural properties was investigated. The lattice constants of samples were measured from X-rays diffraction data. The (311) peak was used to find crystallites size by the Scherrer formula. Structural morphology was observed by scanning electron microscopy. Variation with temperature in electrical resistivity (DC) and drift mobility were also investigated. The variations with frequency and composition in AC electrical properties of prepared samples were determined. The structural and electrical properties demonstrated firm association. Saturation magnetization, coercivity and remanence of the samples were discussed with the help of sharing of cations within crystals.
Abstract: One of the key technologies in future optoelectronics is control of excitons in oxide materials by the coupling with plasmons on noble metal surfaces. Optical properties of ZnO nanowires decorated with Au nanoparticles were studied to understand fundamental mechanism of the coupling and to develop optoelectronic devices with new functionalities. Light intensity at the main peak position in the photoluminescence (PL) spectra of ZnO nanowires was enhanced with the coverage of Au nanoparticles. Lifetime of excitons excited optically decreased by the decoration of Au nanoparticles. Understanding of the coupling between excitons and plasmons leads to optical control of excitons and will pave the way for new type of optoelectronic devices.
Abstract: The bismuth layered structure materials (BLSFs) with general formula of the (Bi2O2)2+(Am-1BmO3m+1)2-, have attracted considerable attention for high-temperature piezoelectric applications. Hot pressing is a useful densifying and texture technique for enhancing the piezoelectric properties. In this present study, four different types (m=1, 2, 3, 4) of ceramics with Aurivillius structure were prepared and the influential factors of textured degree was investigated systematically by hot pressing method. The result indicates that the value of m is larger, the BLSFs ceramics is easier to get high degree of texture and high piezoelectric properties in the parallel of the hot pressing direction.
Abstract: Novel compact interdigital bandpass filters (BPFs) which used multilayer stepped impedance resonators (SIRs)/folded quarter–wavelength resonators were presented. Two measures were taken to reduce the sizes of the proposed filters. Firstly, two resonators (SIRs and folded quarter–wavelength resonators) with novel structures were designed. Secondly, all the designed resonators were located on different dielectric layers. The proposed interdigital BPFs, which were simulated with the high frequency structure simulator (HFSS), show excellent performance and could realize the miniaturization purpose. Furthermore, it is found that the proposed filter with folded quarter–wavelength resonators is more excellent in realizing miniaturization and improving performance than that with SIRs.
Abstract: The material sample was prepared by conventional solid state method and sintered in conventional and microwave furnace at different sintering temperatures. Sintered samples were then subjected to XRD and SEM analysis. X-ray diffraction revealed the formation of single phase material. SEM of fractured cross sectional portion showed that finer grains were formed in case of microwave sintering. The dielectric properties and magnetic properties were recorded for both the samples and both properties were found to improve in microwave sintered samples. There is also a significant improvement in density and magnetic properties by microwave processing.
Abstract: Formation of nano-crystalline p+ silicon (Si) in pinholes through a silicon dioxide layer was achieved by pinning of aluminum through the thin silicon dioxide (SiO2) layer. In addition to opening holes of SiO2 layer by aluminum (Al) pining, amorphous silicon (a-Si) was subsequent deposited on the Al layer and another heated at low temperature (500°C) to allow solid- phase epitaxial growth of p+ Si in the pinholes due to the Al induced layer exchange process. The poly-crystalline p+ Si obtains lower effective surface recombination than the Al back surface field (BSF). The technique demonstrated to result in ohmic contacts with low contact resistance. The evaluation of Al-induced crystallization of a-Si in a-Si/Al bilayer was studied by X-ray diffraction. In this paper, the influence of a-Si/Al thickness ratio on the specific conductivity value and crystalline grain size of the p+ Si thin film is discussed. The obtained results are helpful for a further design of the rear passivation contact in solar cell.
Abstract: The polycrystalline samples of Ba4CaRTi3Nb7O30 (R = Eu, Dy), members of tungsten-bronze family, were prepared by high-temperature solid state reaction method and studied for their dielectric and electrical properties. X-ray diffraction (XRD) analysis reveals the formation of single-phase compounds having orthorhombic crystal structure at room temperature. Microstructural analysis by scanning electron microscope (SEM) shows that the compounds have well defined grains, which are distributed uniformly throughout the sample. Detailed dielectric properties of the compounds as a function of frequency and temperature show that the compounds undergo non-relaxor kind of ferroelectric-paraelectric phase transition of diffuse nature. Ferroelectric, piezoelectric and pyroelectric studies of the compounds have been discussed in this paper. The temperature dependence of dc conductivity of the compounds have been investigated. The conductivity study over a wide temperature range suggests that the compounds have negative temperature coefficient of resistance (NTCR) behaviour.
Abstract: The microwave dielectric properties of ZnTiNb2O8 ( ~34, Qf ~42,500GHz, ~ –52ppm/°C) was reported by Hong et. al. To lower the dielectric loss of ZnTiNb2O8, we studied the systems of (Zn1-xMgx)TiNb2O8 (x=0.02-0.1) ceramics. The manner of equivalent-charge trace substitutions for Zn2+-sites were replaced with Mg2+. In order to achieve more stability, CaTiO3 ( ~ +800ppm/°C) was used to adjust the negative τf of (Zn0.95Mg0.05)TiNb2O8 ( ~ –58ppm/°C). A bandpass filter using coupled microstrip-line resonators have been designd for wireless LAN system such as IEEE 802.11 ( 2.4 or 5 GHz). The response of the implemented filter used 0.8(Zn0.95Mg0.05)TiNb2O8-0.2 CaTiO3 ( ~35.77, Qf ~18,000GHz, ~ +4ppm/°C) dielectric substrates. In this paper, the bandpass filter area designed on 0.8(Zn0.95Mg0.05)TiNb2O8-0.2 CaTiO3 is reduced 88% than FR4 substrates and the near zero τf makes better frequency stability.
Abstract: Some physical properties (such as lattice parameter, curie temperature, ac susceptibility) of Mg1-xZnxFe2O4 (where x = 0.3,0.4,0.5,0.6) ferrites have been studied. Magnesium Zinc Ferrites was synthesized by oxalate co-precipitation method at different synthesis temperature and characterized by X-ray diffraction and far IR absorption techniques, scanning Electron microscopy .The lattice parameter were computed. The X-ray diffraction studies reveal the formations of single phase cubic spinel structure.IR absorption bands are observed around 600 cm-1 and 400 cm-1 on the tetrahedral and octahedral sites respectively. Magnetization parameters such as saturation magnetization, and magnetic moment were calculated and the results are discussed with the help of the existing theories. Saturation magnetization was found to be in the range 2 emu/gm to 8.28 emu/gm when the samples were synthesized below 100°C. The variation of A.C. susceptibility with temperature shows the existence of super paramagnetic nature. The Curie temperature was determined from the measurement of the susceptibility verses temperature. The SEM micrograph shows the uniform distribution of the particles, the average size was estimated to be 0. 350 µm.