Rare Earth Metal Polytellurides RETe1.8 (RE = Gd, Tb, Dy) - Directed Synthesis, Crystal and Electronic Structures, and Bonding Features

Single crystals of the polytellurides RETe1.8 of gadolinium, terbium, and dysprosium were prepared by chemical vapor transport and alkali metal halide flux reactions. To determine proper synthesis conditions for the desired target composition, the binary phase diagram Gd-Te was evaluated by CalPhaD methods. The compounds are isostructural to SmTe1.8 and crystallize in space group P4/n (no. 85) with lattice parameters of a = 966.10(4), 960.00(3), and 957.33(2) pm and c = 1794.15(10), 1785.77(6), and 1779.38(5) pm for GdTe1.8, TbTe1.8 and DyTe1.8, respectively. The structures consist of puckered [RETe] double slabs and planar telluride layers composed of Te-2 dumbbells and linear Te-3 units in accordance with ELI-D based bonding analyses. The latter can be understood as a Te-3(4-) anion. GdTe1.8 is a semiconductor with a bandgap of 0.19 eV/0.17 eV (experimental/calculated). Magnetization data confirm trivalent RE ions and indicate antiferromagnetic order at T-N = 12 K for TbTe1.8 and T-N = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K.