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Carbon Nanotubes: A Review of Synthesis and CharacterizationMethods/Techniques IntroductionWith the discovery of lower dimensional forms of carbon with unique mechanical properties in many areas of technology especially in nanotechnology (Popov V. , 2004), over the years until recent, the discovery was not made about nanostructure, particles and fibers and their applications are also not known. In 1991 carbon nanotubes were discovered by Iijima (Resel Das, Sharifah Bee Abd Hamid, 2015) and they have received much attention because of their usefulness in mechanical (

Initially, three samples of carbon nanotubes (SWCNTs) were synthesized from neem tree material. Afterward, these samples were coated with hexagonal boron nitride (h-BN) to form h-BN and CNT composite (h-BN-CNT). The essence of using h-BN (being a perfect insulator) with armchair SWCNT (being a conductor) is to create an interface between an insulator and conductor. The samples were treated under three different transition metal nanoparticles; silver, iron, and nickel. Thermogravimetric (TGA) analysis reveals that h-BN/CNT is thermally more stable with silver than iron and nickel nanoparticles. TGA profile showed resistance to mass loss at the beginning due to the higher thermal resistivity by the impurity compounds. The DFT calculation, generalized gradient approximation (GGA), and Perdew–Burke–Ernzerhof (PBE) analysis found engineered bandgap energy of 3.4 eV for the synthesized h-BN-CNT heterostructure. Because of its unique structural and electronic properties such as tunable bandgaps, the h-BN-CNT heterostructure may open new ways for manipulating excitons in the CNTs, and thus can be explored to develop various new electronic devices.

Lithium hafnium phosphate LiHf2(PO4)3 (LHP) was synthesized via solid-state synthesis technique. The sintering behavior, structure, and phase composition of the as-prepared sample was analyzed using X-ray diffraction (XRD) characterization technique. The XRD-Rietveld refinement analysis showed that after sintering at low temperatures 500 to 1000 °C, it exhibited various secondary phases. However, a single phase was observed as the sintering temperature increases from 1100 to 1200 °C. LHP sintered at 1100 °C produced real features of sodium superionic conductor type (NASICON-type) with hexagonal crystal axis indicating R-3c space group. The electrical properties were studied using impedance spectroscopy technique. Frequency and temperature dependence behavior of conductivity (ac and dc) and dielectric permittivity were studied. The results obtained describes the conduction mechanism in the system. Electric modulus formalism was performed to investigate the relaxation behavior which showed that as measuring temperature increases, the relaxation frequency increases whereas relaxation time decreases. This behavior explains the hopping mechanism of the charge carriers in the system. Likewise, the correlated barrier hopping model elucidates the dominant hopping mechanism.