IS THERE A RELATION BETWEEN GLASS-FORMING ABILITY AND FIRST SHARP DIFFRACTION PEAK

Available data for the first sharp diffraction peak (FSDP), which is observed in many amorphous substances including glasses, is analysed from the point of view of the glass-forming ability (GFA) of a substance. To clarify the subject, the ways of defining GFA and numerical evaluation are discussed first of all. It is shown that, in contrast to intuition, there is no direct connection between FSDP and GFA. Moreover, a non-glass-forming melt or a glass al the boundary of the glass-forming region may demonstrate strong and narrow FSDP. On the other hand, the obtained correlations between FSDP characteristics (position, intensity, halfwidth) and sample parameters, both internal (chemical composition, short-range order) and external (temperature, pressure), need explanations in terms of models that try to understand the origin of FSDP and corresponding medium-range order in the amorphous state, the glassy state being a particular case.