Crystal structures of the R1.33Ni3Ga8 (R = Tb, Ho, Er, Tm, Lu) compounds

The existence of five new ternary compounds with Gd_1.33Pt₃Al₈-type structure (Pearson symbol hR51, space group R-3m) was established by means of X-ray powder diffraction and energy-dispersive X-ray spectroscopy: Tb_1.33Ni₃Ga₈ (а = 4.2056(1), с = 37.8913(9) Å), Ho_1.33Ni₃Ga₈ (а = 4.19666(9), с = 37.7882(9) Å), Er_1.33Ni₃Ga₈ (a = 4.19290(8), c = 37.7446(8) Å), Tm_1.33Ni₃Ga₈ (a = 4.18819(7), c = 37.6980(7) Å), and Lu_1.33Ni₃Ga₈ (a = 4.1826(1), c = 37.647(1) Å). The structures of the ternary R_1.33Ni₃Ga₈ compounds belong to a family of linear-intergrowth structures with the general formula R_0.67T_nM_{2n + m} and are built from atom layers of the composition R_0.67Ga (R_0.67M), separated by single or double NiGa₂ slabs (TM₂). The layers containing the rare-earth metal atoms are characterized by a disordered distribution of rare-earth metal atoms and Ga-atom triangles.