Abstracts:In the present investigation, we point out the effect of the substrate crystallinity on the growth rate, efficiency, quality and the structure of synthesized aligned carbon nanotubes (CNTs). Three substrates are tested: amorphous alumina (Al2O3), silica (Si/SiO2), and crystalline alumina (sapphire). The growth is carried out using the floating catalyst-CVD process with the ferrocene-toluene solution as precursor. In addition, different concentrations of H2 in the gas supply are investigated. It is observed that the sapphire substrate provides a more homogenous forest of vertically oriented straight nanotubes with small diameter, despite initial horizontal alignment of the nanotubes. In the presence of H2, long arrays of high L/Φ aspect ratio nanotubes were obtained with a reduction of diameter and the number of walls. L/Φ aspect ratio in the case of 7% H2 is c.a. 3600 for sapphire substrate, 1500 and 2000 for alumina and silica amorphous substrate, respectively. When sapphire substrate is used, the increase of H2 to 15% provides the L/Φ aspect ratio of ∼14,000.

Abstracts:(BiFeO3)1− x (α-Fe2O3) x nanocomposites were synthesized from dried gels of BiFeO3 and α-Fe2O3. Samples with x = (0.00 (BiFeO3), 0.25, 0.50 and 1.00 (α-Fe2O3)) were studied using X-rays diffractions (XRD), UV–vis spectroscopy, photoluminescence spectroscopy (PL), electron spin resonance (ESR) and vibrating sample magnetometer (VSM). Amounts of α-Fe2O3 phase were 23 and 35% for samples x = 0.25 and 0.50, respectively. Microstrain of BiFeO3 phase tended to decrease with increasing α-Fe2O3. Optical band gap reduced from 2.42 eV for BiFeO3 to 2.35 eV for sample x = 0.25 and then increased to 2.56 eV for sample x = 0.50. From PL, intensity of near band emission peak of BiFeO3 increased with increasing α-Fe2O3 content. From ESR and VSM, the g-value and magnetization saturation were enhanced with embedding of α-Fe2O3 into BiFeO3.

Abstracts:The nanocrystalline (Fe0.9Co0.1)73.5Si13.5B9− x Nb3Cu1Ge x alloys were obtained by partial devitrification of their amorphous precursors. The influence of partial substitution of B by Ge on the microstrucural evolution of these alloys was studied by means of X-ray diffraction (XRD) and differential scanning calorimeter (DSC). The temperature dependence of initial permeability (μi-T curves) for (Fe0.9Co0.1)73.5Si13.5B6Nb3Cu1Ge3 alloys heating–cooling cycled at 450–650 °C was mainly measured. It was found that the Ge doping into (Fe0.9Co0.1)73.5Si13.5B9Nb3Cu1 alloy can reduce the onset primary crystallization temperature (T x1), enlarge the interval temperature (ΔT x) from 129 °C to 180 °C and improve the high temperature soft magnetic properties, especially for (Fe0.9Co0.1)73.5Si13.5B6Nb3Cu1Ge3 alloy. After annealed at 450–650 °C for the alloy with x = 3, the optimum high temperature magnetic softness was observed in 600 °C-annealed sample, the μi above 1000 at 10 kHz can be kept up to 550 °C, which is due to the higher crystallization phase volume fraction and the thinner amorphous layer thickness and an enhancement of the exchange stiffness in the intergranular region.