| Abstract
| - The seven new isostructural quaternary uranium chalcogenides KCuUS3, RbCuUS3, RbAgUS3, CsCuUS3, CsAgUS3, RbAgUSe3, and CsAgUSe3 were prepared from solid-state reactions. These isostructural materials crystallize in the layered KZrCuS3 structure type in the orthorhombic space group Cmcm. The structure is composed of UQ6 octahedra and MQ4 tetrahedra that share edges to form 2∞[UMQ3−] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing AQ8 bicapped trigonal prisms. There are no Q−Q bonds in the structure, so the formal oxidation states of A/U/M/Q may be assigned as 1+/4+/1+/2−, respectively. CsCuUS3 shows semiconducting behavior with thermal activation energy Ea = 0.14 eV and σ298 = 0.3 S/cm. From single-crystal absorption measurements in the near IR range, the optical band gaps of these compounds are smaller than 0.73 eV. The more diffuse 5f electrons play a much more dominant role in the optical properties of the AMUQ3 compounds than do the 4f electrons in the AMLnQ3 compounds (Ln = rare earth). Periodic DFT spin band-structure calculations on CsCuUS3 and CsAgUS3 establish two energetically similar antiferromagnetic spin structures and show magnetic interactions within and between the layers of the structure. Density-of-states analysis shows M−Q orbital overlap in the valence band and U−Q orbital overlap in the conduction band.
- The new AMUQ3 compounds KCuUS3, RbCuUS3, CsCuUS3, CsAgUS3, RbAgUSe3, and CsAgUSe3 crystallize in the layered KZrCuS3 structure type. These compounds are semiconductors with optical band gaps smaller than 0.73 eV. Density-of-state analysis shows M−Q orbital overlap in the valence band and U−Q orbital overlap in the conduction band.
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