Ordered U(Al, Si)₃phase: Structure and bonding

Recently the crystal structure of a new stable ordered U(Al, Si)₃phase was solved using electron crystallography and powder X-ray diffraction. The proposed atomic structure included 7 Wyckoff sites. 16m site was assigned to uranium atoms, while others could not be certainly assigned to either silicon or aluminum atoms due to similar scattering factors. In the current research, ab initio calculations, via Density Functional theory (DFT), were used for full structure solution. Assuming that only one type of elements occupies each specific Wyckoff position, the silicon and aluminum positions were assigned. It was found that compared to aluminum, the silicon occupies the closest sites to uranium. The optimized volume and the relaxed atomic positions calculated in the framework of DFT are in good agreement with the experimental data. Density of States (DOS) analysis shows stronger bonding between uranium and silicon compared to the bond between uranium and aluminum in the energetically preferable structure.