Synthesis, crystal structure, theoretical, and resistivity study of BaUSe₃

The black-colored compound BaUSe₃ has been synthesized at 1173 K by a stoichiometric reaction of the elements in a CsCl flux. BaUSe₃ crystallizes in the GdFeO₃ structure type. There is no change in structure between 100 and 298 K. The U atoms in this structure are octahedrally connected to six Se atoms. Each octahedral unit shares all six corners with neighboring octahedra, forming a three-dimensional network. BaUSe₃ can be charge balanced as Ba²⁺U⁴⁺(Se^2-)₃. DFT electronic structure calculations found BaUSe₃ to be antiferromagnetic in its ground state and to be a semiconductor with a band gap of 2.5 eV. The band gap is inconsistent with the black color of the material and with the small activation energy of 0.12(1) eV obtained from resistivity measurements. A UV-vis spectrum indicated that there was no band gap above 1 eV. It is possible that, for BaUSe₃, intrinsic and extrinsic impurities from the flux create midgap states that lead to the experimentally measured narrow optical gap. More likely, BaUSe₃ presents a challenge to DFT calculations as applied to 5f materials.