Structure of levitated Si-Ge melts studied by high-energy x-ray diffraction in combination with reverse Monte Carlo...

The short-range order in liquid Si, Ge and binary Si-Ge_1-alloys (x= 0.25, 0.50, 0.75) was studied by x-ray diffraction and reverse Monte Carlo simulations. Experiments were performed in the normal and supercooled liquid states by using the containerless technique of aerodynamic levitation with CO₂laser heating, enabling deeper supercooling of liquid Si and Si-Ge alloys than previously reported. The local atomic structure of liquid Si and Ge resembles theβ-tin structure. The first coordination numbers of about 6 for all compositions are found to be independent of temperature indicating the supercooled liquids studied retain this high-density liquid (HDL) structure. However, there is evidence of developing local tetrahedral ordering, as manifested by a shoulder on the right side of the first peak inS(Q) which becomes more prominent with increasing supercooling. This result is potentially indicative of a continuous transition from the stable HDLβ-tin (high pressure) phase, towards a metastable low-density liquid phase, reminiscent of the diamond (ambient pressure) structure.