Structural study of CoxGe100−x alloys produced by mechanical alloying

Two alloys of the Co-Ge system were produced by mechanical alloying starting from the elemental powders in the compositions Co₂₀Ge₈₀ and Co₄₀Ge₆₀. The crystalline structures of the Co_xGe_100−x (x=20, 40) alloys obtained were investigated using the X-ray diffraction (XRD) technique. The measured XRD patterns showed the presence of the peaks corresponding to the crystalline m-CoGe phase and also to the high pressure and temperature phase c-CoGe in the as-milled sample for Co₂₀Ge₈₀, although it was milled at room temperature and pressure. For Co₄₀Ge₆₀, the crystalline Co₃Ge₂ phase was obtained, and structural data for all phases were determined by means of a Rietveld refinement procedure. The thermal stability of the phases was investigated performing a heat treatment of the alloys at 450 °C for 6 h and, after that, new XRD measurements were collected and were also studied using a Rietveld refinement procedure. The m-CoGe and Co₃Ge₂ phases seem to be very stable, but the relative amount of c-CoGe decreases a little, indicating a less stable phase, which can be explained by the fact that it is produced usually under extreme conditions.