Crystal Chemistry of Ternary Rare Earth Transition Metal Carbides: Studies of the Tb-Fe-C System at 800°C

Abstract

The isothermal section of the phase diagram of Tb–Fe–C system at 800 °C was studied in the full concentration range using powder X-ray phase and structure analyses, and energy-dispersive X-ray spectroscopy. Six ternary compounds Tb1.88Fe14C, Tb13Fe10C13, TbFeC2, Tb15Fe8C25, Tb5.64Fe2C9, Tb2FeC4 and a limited solid solubility of carbon in the crystal structure of the binary parent compound Tb2Fe17Cх (0≤ х ≤0.8) have been found to exist at 800 °C. The crystal structures of two new ternary carbides have been determined by means of powder X-ray diffraction: Tb15Fe8C25 with structure type Er15Fe8C25, space group P321, a = 11.9706(3) Å, c = 5.1733(2) Å, RB(I) = 0.07, RP = 0.06, RPw = 0.08, and Tb13Fe10C13 with structure type Gd13Fe10C13, space group P3121, a = 9.1800(9) Å, c = 23.703(5) Å, RB(I) = 0.04, RP = 0.16. Both compounds are representatives of the carbometalate class of complex carbides. Tb15Fe8C25 displays an itinerant ferro-or ferrimagnetic ordering of the Fe 3d-moments below TM ≈ 50 K while Tb 4f-moments remain essentially paramagnetic at least down to about 10 K.