Seminars Archive

Possible liquid-liquid transitions in silicon and boron

Abstract
We present x-ray diffraction, inelastic x-ray scattering and electrodeless conductivity measurements on liquid silicon and boron. The samples are suspended by aerodynamic levitation and heated by CO2 lasers. Both elements exhibit a contraction on melting, accompanied by a considerable decrease in longitudinal sound velocity. On the other hand the entropy increase on melting B is only 9.6 J.mol-1.K-1, a typical value for most elements, while it is three times larger for Si, and the changes in structure and conductivity much more modest in B than in Si. While our results for Si are consistent with the liquid-liquid phase transition proposed by Angell and co-workers, melting in B appears to be more similar to the transition between solid and supercooled tetrahedral liquid Si predicted by computer simulations.