Stuart Ansell

Structure of supercooled liquid silicon

We report x-ray diffraction measurements of the structure factor S(Q) and the radial distribution function g(r) of levitated liquid silicon in the stable and supercooled states. Supercooling results in a sharpening of the first peak in S(Q) and shift to an 8% higher Q value, the appearance of a double shoulder on the high-r side of the first peak in g(r), a sharpening of the first peak in g(r) and a decrease in coordination number. These changes are consistent with a significantly enhanced degree of covalent bonding.

The electrical conductivity of levitated liquids

The electrical conductivities of aerodynamically levitated liquid spheres have been determined by an electrodeless method. It is shown that this technique is reliable over a wide range of temperatures; results are presented for a variety of systems including metals, semiconductors at room temperature and at their melting points, and solid and liquid Al2O3.

Ionic structure in the aqueous electrolyte glass

The difference methods of neutron diffraction and isotopic substitution were applied to and in the aqueous lithium chloride glass at 120 K (the glass transition ). Results for the ionic hydration show that structural changes are more evident for the coordination than for the coordination. At the level of the anion - anion structure there is an appreciable increase in the nearest-neighbour coordination number over that in the liquid which suggests a greater degree of correlation between the anion and the water molecules. A model of the ionic structure is proposed to explain the relative ease of glassification of concentrated aqueous lithium chloride solutions.

X-ray diffraction on levitated liquids : application to liquid 80%Co-20%Pd alloy.

Abstract We describe the use of a novel levitation apparatus for structural studies on liquid materials using synchrotron X-ray scattering. The apparatus has been employed in investigations of the structural properties of a range of liquid ceramic, metallic, and semiconducting materials in the temperature range of 1000–3500 K. The apparatus uses conical nozzle levitation to stably position solid and liquid specimens at temperatures >1000 K. Specimens are heated with a 270 W, CO2 laser to melt, overheat and supercool the specimens in the desired temperature range. We report the first measurements of the total structure factor, S(Q), and pair distributions function, G(r), of liquid 80%Co–20%Pd in both the normal and supercooled states. This alloy has been previously reported to exhibit magnetic order in the supercooled liquid state. No abrupt structural change was observed as the alloy was supercooled, although it was not possible to cool the liquid to temperatures at which magnetic ordering has been reported.

The structure of supercooled elemental liquids

Recent measurements of the atomic structure of supercooled liquid B, Ni, Si and Zr show a short-range structure similar to that of the nucleating crystalline phases. As the liquids are supercooled, the coordination numbers and interatomic distances increase, decrease or remain essentially constant to approach the values characteristic of the crystals that nucleate from the liquid. Further support for the present observations comes from prior results on Ga, Ge and Pd. This observed correlation between supercooled liquid and crystalline structures provides new insight into nucleation phenomena. The trends in the experimental results and the relationship between the short-range structural properties of supercooled elemental liquids and their crystalline counterparts are discussed.