Specific Features of Phase Formation and the Crystal Structures of Compounds in the Ternary Tm-Cu-Si System.

The methods of X-ray phase diffraction and structural diffraction analyses and, partially, the method of microstructural analysis are used to study the phase equilibria in the ternary Tm-Cu-Si system and plot the isothermal section of the phase diagram of this system at 870°K. The existence of seven ternary compounds at this temperature, namely, TmCuSi , TmCuSi , TmCuSi, TmCuSi, TmCuSi , TmCuSi, and TmCuSi is established. It is shown that solely the TmCu binary compound dissolves 5 at.% Si. At the same time, we did not detect any noticeable solubility of the third component in the other binary compounds. The structural parameters are determined for the following ternary compounds: TmCuSi (ST ScNiSi , SG P6 / mmc , PS hP36, a = 8.3898(6), c = 8.6425(7) Å, R = 0.0606, R = 0.0442, R = 0,0351, R = 0.0570, and χ = 1.74), TmCuSi (ZrBeSi, P6 / mmc , hP36, a = 4.1399(3), c = 7.1471(7) Å, R =0.0493, R = 0.0449, R = 0.0698, R = 0.0930, and χ = 1.98), and TmCuSi (AlB , P6/ mmm , hP3, a = 3.9799(3), c = 3.9197(4) Å, R = 0.0543, R = 0.0293, and χ = 1.01). The specific features of the Tm-Cu-Si system and its relationship with the previously studied R-Cu-Si systems are analyzed. [ABSTRACT FROM AUTHOR]