Papers by Author: J. Neuefeind

Abstract: The glass transition and the phase formation during crystallization of the Zr₅₂Ti₅Cu₁₈Ni₁₅Al₁₀ bulk metallic glass were followed in situ by high-temperature X-ray diffraction using synchrotron radiation at the high energy beam-line BW5 ( λ = 0.01040 nm) at the storage ring DORIS (HASYLAB, Hamburg). The experimental set-up enables to record intensities in transmission up to scattering vectors q of 200 nm ^-1 with a measuring time of 20 s per diagram. The crystallization starts with the formation of an extremely fine nanostructure followed by the transformation into tetragonal NiZr₂-type crystals plus an unknown phase. Both phases are metastable and transform at about 1123 K into the stable equilibrium phases. The temperature dependence of the structure factor S(q) of the glass can be well described within the framework of the Debye theory. At the glass transition the first derivative dS(q)/dT changes. A Debye temperature Θ = 412 K was estimated for the glassy, and Θ = 162 K for the liquid state of the Zr₅₂Ti₅Cu₁₈Ni₁₅Al₁₀ alloy. The short-range order of the glass, of the supercooled liquid state, and of the equilibrium melt at T = 1193 K is found to be quite similar.

Abstract: A considerable fraction of atoms in nanosize particles is at the grain surface (due to the small size of the crystals). We assume that the surface atoms form a separate structural phase relative to the bulk of the grain (the core). Therefore, one set of the lattice parameters characterizing a nanocrystal may be inadequate for a unique description of its structure. An alternative evaluation of diffraction data of nanocparticles, based on the 'apparent lattice parameter' is proposed. Based on this new methodology it is shown that real nano-crystals constitiute a complex, more than a one-uniform-phase structure.