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 870A degrees 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 P6(3) /mmc , PS hP36, a = 8.3898(6), c = 8.6425(7) , R (B) = 0.0606, R (F) = 0.0442, R (P) = 0,0351, R (wp) = 0.0570, and chi(2) = 1.74), TmCuSi (ZrBeSi, P6(3) /mmc , hP36, a = 4.1399(3), c = 7.1471(7) , R (B) =0.0493, R (F) = 0.0449, R (P) = 0.0698, R (wp) = 0.0930, and chi(2) = 1.98), and TmCu0.5Si1.5 (AlB2 , P6/mmm , hP3, a = 3.9799(3), c = 3.9197(4) , R (I) = 0.0543, R (P) = 0.0293, and chi(2) = 1.01). The specific features of the Tm-Cu-Si system and its relationship with the previously studied R-Cu-Si systems are analyzed.