ELECTRONIC BAND-STRUCTURE OF TH3NI3SB4 AND TH3X4 (X=P, AS, SB)

In order to clarify the origin of the semiconductor like behavior of U3Ni3Sb4, one-electron energy band structures for the isostructural Th3Ni3Sb4 and the Th3P4 type Th3X4(X = P, As, Sb), which belong to the same space group, are calculated by the self-consistent APW method with the local density approximation. The calculated results for Th3X4 show that the compounds are the narrow gap semiconductor or semimetal; the valence bands are derived from the X p states and the conduction bands from the Th 6d states. Th3Ni3Sb4 is also the semiconductor and the valence bands consist of the Ni 3d and Sb 5p states. Due to the mixing between the Ni 3d and Th 6d states, the empty Th 6d conduction band is shifted up resulting a gap of 0.36 eV. This result explains reasonably why U3X4 is semimetal but U3Ni3Sb4 is semiconductor with a gap of 0.2 eV.