Jan Sakowski

Structural behavior of Pd40Cu30Ni10P20 bulk metallic glass below and above the glass transition

The thermal behavior of the structure of Pd40Cu30Ni10P20 bulk metallic glass has been investigated in situ through the glass transition by means of high-temperature x-ray synchrotron diffraction. The dependence of the x-ray structure factor S(q) of the Pd40Cu30Ni10P20 glass on temperature follows the Debye theory up to the glass transition with a Debye temperature θ=296 K. Above the glass transition temperature Tg, the temperature dependence of S(q) is altered, pointing to a continuous development of structural changes in the liquid with temperature. The atomic pair correlation functions g(r) indicate changes in short-range-order parameters of the first and the second neighborhood with temperature. The temperature dependence of structural parameters is different in glass and in supercooled liquid, with a continuous behavior through the glass transition. The nearest-neighbor distance decreases with temperature, changing the slope at Tg. The interatomic distances of higher coordination shells expand analogo...

Structural behavior of Zr52Ti5Cu18Ni15Al10 bulk metallic glass at high temperatures

The structural behavior of the Zr52Ti5Cu18Ni15Al10 bulk glass-forming alloy has been investigated in situ by means of high-temperature x-ray synchrotron diffraction. The dependence of the structure factor of the glass can be well described with a Debye–Waller factor and a Debye temperature θ=412 K. At the glass transition, the structure factor significantly decreases due to additional thermal excitations. The extrapolation of the structure factor of the supercooled liquid to temperatures above the liquidus curve is in agreement with experimentally determined values of the melt. 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. The formation of complex chemically ordered clusters in the melt is proposed to be essential for the high-glass-forming ability of this alloy.

Short-range and medium-range order in solid and molten metaphosphate glasses

X-ray diffraction measurements of molten binary metaphosphate glasses are described. The changes in the short-range order in the temperature range greater than the glass transition temperature, Tg, are discussed and the differences between the glass and liquid structures are emphasized. The phenomenon of a thermally inducible peak at the smallest Q nm−1 which exists for sodium metaphosphate, but is not detected for diffraction from magnesium or calcium metaphosphate, is regarded as a first sharp diffraction peak (FSDP) and interpreted in terms of the cluster–void picture. The amplitude of the FSDP increases with temperature due to the increase of scattering contrast by the thermal expansion of the NaOn polyhedra. We assert that the FSDP is a sufficient, but not necessary signature of medium-range order.

Structure of Zr52Ti5Cu18Ni15Al10 Bulk Metallic Glass at Elevated Temperatures

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.

Structural Changes in Two Different Types of Oxide Glass Melts: Borates and Metaphosphates

Abstract X-ray diffraction experiments of molten oxide glasses, which give new insights into the structure of melts, were carried out. Using modern means (synchrotron radiation, image plates, container-less high-temperature technique) it could be shown that the short range order of melt and solid glass is often qualitatively different. If vitreous B2O3 or binary borate glasses with low content of network modifier are heated up above Tg , the network topology begins to alter. With rising temperature more and more of the boroxol groups are replaced by independent B0 3 groups. While melting a metaphosphate glass, how-ever, structural changes of another kind take place. In solid glass the environment of the network modifier ions is similar to the one found in crystalline modifications, and their distances to the surrounding PO4 tetrahedra have narrow distributions. In the melt, however, these distances scarcely become evident, probably owing to the increased thermal motion of the modifier ions.