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 CoxGe100−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.