The U5+ compound Ba9Ag10U4S24: Synthesis, structure, and electronic properties

• Black crystals of Ba9Ag10U4S24 have been made by direct combination of BaS, Ag, U, and S at 1273 K.
• Ba9Ag10U4S24 contains U5+ and charge balance is achieved with 9 Ba2+, 10 Ag1+, 4 U5+, and 24 S2−.
• DFT calculations predict an antiferromagnetic ground state and a band gap of 2.1 eV.
• The compound is a semiconductor with activation energies ranging from 0.03(1) eV to 0.08(1) eV.

Black crystals of Ba9Ag10U4S24 have been made by direct combination of BaS, Ag, U, and S at 1273 K. This compound crystallizes in a new structure type in the space group C4v10−I4cm of the tetragonal system with four formula units in a cell with lattice constants a=13.9189(6) Å and c=23.7641(11) Å (V=4604(5) Å3). Multiphoton Luminescence Spectroscopy measurements are consistent with the noncentrosymmetric nature of the structure. In the structure each U atom is octahedrally coordinated by six S atoms, whereas three of the five crystallographically independent Ag atoms are tetrahedrally coordinated to four S atoms, another has a seesaw coordination to four S atoms, and the last has a triangular coordination to three S atoms. The overall structure consists of the three-dimensional stacking of the US6, AgS4, and AgS3 polyhedra to leave channels in which Ba atoms reside. Based on the values of the U–S interatomic distances, the compound Ba9Ag10U4S24 contains U5+ and charge balance is achieved with the formal oxidation states of 9 Ba2+, 10 Ag1+, 4 U5+ and 24 S2−. DFT calculations predict an antiferromagnetic ground state and a band gap of 2.1 eV. Resistivity measurements indicate that the compound is a semiconductor with a complex activation mechanism and activation energies ranging from 0.03(1) eV to 0.08(1) eV.

General view of the Ba9Ag10U4S24 structure.Figure optionsDownload as PowerPoint slide