Ternary system Tm-Cu-Ge: isothermal section of the phase diagram at 870 K and crystal structures of the compounds

The isothermal section of the Tm-Cu-Ge phase diagram at 870 K was constructed using X-ray phase analysis. The existence of three ternary compounds was confirmed: TmCu2Ge2 (structure type CeAl2Ga2, space group I4/mmm, Pearson code tI10, a=3.99155(8) A, c=10.3285(2) A), Tm2CuGe6 (structure type Ce2CuGe6, space group Amm2, Pearson code oS18, a=4.061(1) A, b=3.957(4) A, c=20.76(2) A) and Tm6Cu8Ge8 (structure type Gd6Cu8Ge8, space group Immm, Pearson code oI22, a=13.7407(3) A, b=6.5995(1) A, c=4.1368(1) A). A new ternary copper germanide TmCu1.24Ge0.76 (structure type CaIn2, space group P63/mmc, Pearson code hP6, a=4.42254(8) A, c=7.0477(2) A) was found. The crystal structures of TmCu2Ge2, Tm6Cu8Ge8 and TmCu1.24Ge0.76 were refined by full-profile Rietveld method using X-ray powder diffraction data. The binary compound Tm0.9Ge2 (structure type ZrSi2) dissolves up to 5 at.% of Cu. The lattice parameters refined for the sample Tm31Cu5Ge64 (a=4.042(1) A, b=15.793(4) A, c=3.906(2) A) slightly increased, compared with Tm0.9Ge2. The solubility of the third component in the other binary phases was found to be negligible