Articles you may be interested inEffects of microwave power on the structural and emission properties of hydrogenated amorphous silicon carbide deposited by electron cyclotron resonance chemical vapor deposition
The solidification microstructures of three nine-element Zr-Ni-based AB 2 type C14/C15 Laves hydrogen storage alloys are determined. The selected compositions represent a class of alloys being examined for usage as an MH electrode in nickel metal-hydride batteries that often have their best properties in the cast state. Solidification is accomplished by dendritic growth of hexagonal C14 Laves phase, peritectic solidification of cubic C15 Laves phase, and formation of cubic B2 phase in the interdendritic regions. The B2 phase decomposes in the solid state into a complex multivariate platelike structure containing Zr-Ni-rich intermetallics. The observed sequence C14/C15 upon solidification agrees with predictions using effective compositions and thermodynamic assessments of the ternary systems, Ni-Cr-Zr and Cr-Ti-Zr. Experimentally, the closeness of the compositions of the C14 and C15 phases required the use of compositional mapping with an energy dispersive detector capable of processing a very high X-ray flux to locate regions in the microstructure for quantitative composition measurement and transmission electron microscope examination.
The complex dielectric function of the three stoichiometric compositions GeSb4Te7, GeSb2Te4, and Ge2Sb2Te5 has been measured by spectroscopic ellipsometry in the energy range of 1.4–5.1 eV. Each composition was measured in the amorphous and in the two crystalline states, the metastable face-centered-cubic and the stable hexagonal phases. The complex dielectric function shows strong differences between the amorphous and the crystalline samples, these differences are responsible for the drastic contrast in the reflectivity spectra. The ellipsometric spectra are fitted with models which fulfilling the Kramers–Kronig relations. Thus the Forouhi–Bloomer model was used for the amorphous samples and the Lorentz harmonic oscillator model for the crystalline samples. The temperatures at which the phase transformations are achieved were determined by measuring the ac electrical resistance at 100 Hz while the samples were heated. The temperature derivative of the electrical conductivity shows two well defined peaks at critical temperatures where the phase transformation occurs as is revealed by the x-ray data.
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