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, Tm3Cu11Si4 , TmCu2Si2 , Tm6Cu8Si8, TmCuSi, TmCu0.5Si1.5 , TmCu0.39–0.09Si1.61–1.91, and TmCu0.05Si1.66 is established. It is shown that solely the TmCu2 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: Tm3Cu11Si4 (ST Sc3Ni11Si4 , SG P63 /mmc , PS hP36, a = 8.3898(6), c = 8.6425(7) A, R B = 0.0606, R F = 0.0442, R P = 0,0351, R wp = 0.0570, and χ2 = 1.74), TmCuSi (ZrBeSi, P63 /mmc , hP36, a = 4.1399(3), c = 7.1471(7) A, R B =0.0493, R F = 0.0449, R P = 0.0698, R wp = 0.0930, and χ2 = 1.98), and TmCu0.5Si1.5 (AlB2 , P6/mmm , hP3, a = 3.9799(3), c = 3.9197(4) A, R I = 0.0543, R P = 0.0293, and χ2 = 1.01). The specific features of the Tm–Cu–Si system and its relationship with the previously studied R–Cu–Si systems are analyzed.