X-rays investigation of the α→β phase transition in the GexSi1−x solid solutions at high pressure

We have investigated the α → β phase transition in the solid solution Ge_xSi_1?x using a diamond anvil cell and the energy dispersive x-ray diffraction technique. The transition pressure p_T obtained from samples with x=0, 0.345, 0.543, 0.774, 0.897 and 1 shows a clear nonlinear dependence on the Ge concentration x; p_T is always larger than expected on the basis of a linear interpolation between the p_T-values of pure Si and Ge. In addition to that we have obtained the volume of the α-phase (diamond structure) and of the β-phase (white- tin structure) at p_T. The first one is linear in x, whereas the second one exhibits a nonlinear x-dependence. These results are discussed on the basis of recent pseudopotential calculations by Soma et al.