High-temperature ordering of structural vacancies in the cobalt-rich portion of the binary system Co-Ge

X-ray powder diffraction analysis, macroscopic density measurement and light microscopical methods were used for the investigation of the ordering of structural vacancies in the high-temperature phase Co3Ge2. The heat treated alloy of the composition Co58Ge42 (bulk specimen: 43 h at 700 deg. C; powder specimen: 43 h at 700 deg. C) showed the crystal structure of Co3Ge2: Pearson-Parthe symbol (hP22-1.7), space group P63/mmc, Fe2-xGe type, a = 7.7541(8) A, c = 4.991(1) A. The distribution of structural vacancies as determined for the high-temperature phase Co3Ge2 differs from the one for the quasihomologous phase Ni19Ge12. This effect is caused by the difference in filling of the 3d band for the late transition metals cobalt and nickel