The isothermal section of the Tb–Co–Sb ternary system at 500°C

Abstract The isothermal section of the phase diagram of the Tb–Co–Sb system at 500 °C was investigated mainly by X-ray powder diffraction. The binary compounds: Tb 2 Co 17 , Tb 2 Co 7 , TbCo 3 , TbCo 2 , Tb 4 Co 3 , Tb 12 Co 7 , Tb 3 Co, CoSb, CoSb 2 , CoSb 3 , Tb 2 Sb 5 , TbSb, Tb 4 Sb 3 and Tb 5 Sb 3 have been confirmed at 500 °C. No ternary compound was found in this system. The binary compound Tb 2 Sb 5 instead of TbSb 2 was found in the Tb–Sb binary system. The compound Tb 2 Sb 5 is of Ho 2 Sb 5 -type structure (monoclinic, space group P 2 1 / m ) with a = 1.31108(3), b = 0.416979(8), c = 1.46490(3) nm, β = 102.344(1)°. The homogeneity range of CoSb is about 2.0 at.% Sb at 500 °C. The maximum solid solubility of Tb in CoSb is less than 1.0 at.%. The maximum solid solubility of Tb in CoSb 3 at 500 °C is small (less than 0.4 at.%), while the homogeneity ranges of the other single-phase regions are non-observable.