Pressure-induced structural change in liquid GeTe and Liquid GeSe

X-ray diffraction has been measured up to 19 GPa for liquid GeTe and up to 15 GPa for liquid GeSe using synchrotron radiations. Static structure factor S(Q) and pair distribution function g(r) was obtained. Both S(Q) of liquid GeTe and liquid GeSe change their shape with increasing pressure, indicating anisotropic contraction of the local structure. A sharp change in S(Q) and g(r) was observed in liquid GeTe between 1.8 GPa and 4.0 GPa. Pressure dependences of S(Q) and g(r) of liquid GeSe change around 6 GPa. In liquid GeSe a small pre-peak was observed around 1.2 A-1 up to 1.7 GPa which suggests the presence of the medium range order of covalent bond network. With increasing pressure the Peierls-type distortion becomes small and the bond angle decreases; the local structure becomes a rhombohedral structure. These pressure dependences of the structure of liquid GeTe and liquid GeSe are different from those of the crystals. These results are compared with those of other liquids and discussed in relation to the bonds between atoms in the liquids.