Papers by Keyword: Hexagonal

Abstract: In this article, the structural, microstructural, and dielectric properties of Lead- free perovskite ceramic Bi_0.5(Na_0.78K_0.22)_0.5TiO₃ [BNKT] have been reported. The material was synthesized through the solid-state reaction method. The compound formed is found to have a hexagonal structure, confirmed by XRD analysis of the sample. The microstructural analysis of the compound revealed the polycrystalline nature of the ceramic having quasi-cubic grain morphology with distinct grain boundaries. From the dielectric study, it was found that the dielectric constant increases with temperature and attained maximum value at temperature T_c = 335° C, after which it decreased. The frequency independence of transition temperature (T_c) suggested the classic ferroelectric behaviour of the compound. The broad dielectric peak around transition temperature confirms the relaxor behaviour of the compound as well as diffused phase transition at T_c. The value of the relative permittivity and loss tangent at ambient temperature for 1kHz frequency is 627 and 0.223 respectively. The synthesized material can be utilized for the fabrication of capacitors and energy storage applications.

Abstract: Zinc oxide (ZnO) thin films are synthesized by using modified successive ionic layer adsorption and reaction techniques (SILAR) on glass substrate at room temperature. These as deposited thin films are characterized for structural, compositional, surface morphology and optical characterizations using X-ray diffraction (XRD), energy dispersive X-ray absorption spectra analysis (EDAX), atomic force microscopy (AFM) and Uv-vis absorption spectroscopy. From XRD pattern; the low intensity peaks indicate that the films consist coarsely fine grains and/or amorphous in nature. The diffraction peaks observed at 2θ = 31.71 ̊, 36.27 ̊and 56.29 ̊ are attributed to (100), (101) and (110) planes having hexagonal phase while EDAX shows elemental traces for Zn and O. Surface morphology observed from the AFM corresponds granular shape evenly distributed over substrate surface.

Abstract: The electrical characteristics of the 1.2-kV rated 4H-SiC accumulation-channel split-gate octagonal cell MOSFET (SG-OCTFET) are experimentally compared with linear, square, hexagonal, octagonal, and compact-octagonal cell topologies. The specific on-resistance of the SG-OCTFET is 52% larger than the conventional linear cell topology. However, the SG-OCTFET has: (i) high-frequency figure-of-merit HFFOM[R_on×C_gd] 9.4×, 6.1×, 2.6×, 2.0×, and 1.8× superior to the square, hex, linear, octagonal, and compact-octagonal cells; (ii) fastest switching performance among all cell topologies, with 26% smaller switching energy loss than the conventional linear cell topology; and (iii) short circuit capability 1.5× longer than the conventional linear cell topology. The SG-OCTFET device is therefore an optimum candidate for high frequency applications of SiC MOSFETs.

Abstract: A simple method to synthesized nanoparticles was satisfied by reduction of tetrachloroauric acid in the presence of palm oil fronds extracts as capping and reduced agents. The as-synthesized gold nanoparticles structures have a triangular and hexagonal shape that are of tens of nanometre in size. It was realized that good control shape of nano-hexagonal gold nanoparticles were obtained from nano-triangular gold nanoparticles in the absence of any soft template. The production techniques of the gold nanoparticles were examined by using UV-vis spectroscopy, EFTEM and XRD patterns, which showed peaks at (111), (200), (220), (311) and (222), that described the preferential structure of the AuNPs as face-centered cubic crystal

Abstract: Magnetic composite comprising zinc ferrite and barium hexaferrite; BaFe₁₂O₁₉/ZnFe₂O₄ nanoparticles having super paramagnetic nature were synthesized by co-precipitation of iron, zinc and barium chloride salts using 7.5 M sodium hydroxide solution. The resulting precursors were heat treated (HT) at 800 and 1200°C for 4 h in nitrogen atmosphere. The hysteresis loops showed an increase in saturation magnetization from 1.040 to 52.938 emu/g with increasing heat treatment (HT) temperatures. The ‘as synthesized’ particles have size in the range of 20–22 nm with spherical and needle shapes. Further, these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plate shape with increase in HT temperatures. The effect of such a systematic morphological transformation of nanoparticles on microwave absorption properties were estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite reaches-23.12 dB (more than 99% power attenuation) at 10.46 GHz which make it a potential material in the area of stealth technology.

Abstract: We give here an overview of our recent work on growth of rhombohedral boron nitride (r-BN) thin films on SiC substrates by chemical vapor deposition (CVD). We demonstrate the growth of twinned r-BN on various SiC polytypes at 1500 °C, using H₂ as carrier gas and triethyl boron and ammonia as precursors with an N/B ratio of ~ 640. The epitaxial relation with various substrates is determined from XRD and TEM. Adding Si to the gas phase stabilizes the r-BN phase but does not alter the electric properties of the material which remains electrically insulating.

Abstract: The crystalline structure of the hexagonal Ba (Ti_0.95Fe_0.05)O_3−δ (BTF) ceramic were directly measured using a temperature-dependent XRD technique. Different from the traditional structural transitions of rhombohedral-orthorhombic (−90 °C), orthorhombic-tetragonal (−10 °C), and tetragonal-cubic (i.e., the Curie temperature T_C = 130 °C) for BaTiO₃, the phase transition from hexagonal to any phase above for BTF cannot occur at T_C even up to 300 °C. Increasing temperature cannot give rise to the occupation of oxygen vacancies by environmental oxygen absorbed. The lattice electro-neutrality maintained by Fe³⁺-V_O-Fe³⁺ defect complexes is predominant in BTF. This experiment clarifies the phase stability of the hexagonal perovskite structure above T_C up to 300 °C.

Abstract: Hexagonal Ni micro/nanoplates were successfully prepared via a facile hydrothermal route using the polyvinylpyrrolidone as structure-directing agent. It has been verified from x-ray powder diffraction and transmission electronic microscopy that as-prepared products with high purity and fine dispersity belong to face-centered cubic microstructure of nickel metal. The magnetic hysteresis loop of the hexagonal Ni micro/nanoplates exhibits the ferromagnetic characteristics, and its coercivity increases by 25 % in comparison with the bulk nickel materials. The possible mechanism of the formation of hexagonal micro/nanoplates was suggested.

Abstract: For random distribution of large-scale wireless sensor network (WSN), the hexagonal distributed cluster-based multi-hop routing protocol based on event triggering (HDCMET) is proposed. Triggered by events, nodes optimize a cluster head, according to the rest energy. A cluster head chooses other nodes for a hexagon, with distance to the cluster, energy and so on. Simulation results show that this protocol prolongs the network life in total, improving the network performance in large-scale WSN, compared with the low energy adaptive cluster hierarchy (LEACH).

Abstract: The texture and microstructure evolution during uniaxial compression of Zircaloy-4 at 500C has been studied. X-ray diffraction was used to measure the bulk texture compressive after strains of 20% and 50%. Early stages of texture evolution involve the strengthening of the fibre through the action of prismatic slip. With further deformation, the basal poles move toward the rolling direction from the normal direction as a result of a non-prismatic slip system. A detailed EBSD study in a small region showed that the grains of the fibre are more stable than those of the fibre. The latter rotates further during deformation and shows a greater spread of grain average misorientation (GAM). This could be due to a greater accommodation of plastic strain in these grains and/or a difference in recovery rates between the two fibres.