Ab initio study of bilateral doping within the MoS2-NbS2 system

We present a systematic study on the stability and the structural and electronic properties of mixed molybdenum-niobium disulphides. Using density-functional theory we investigate bilateral doping with up to 25% of MoS2 (NbS2) by Nb (Mo) atoms focusing on the precise arrangement of dopants within the host lattices. We find that over the whole range of considered concentrations, Nb doping of MoS2 occurs through a substitutional mechanism. For Mo in NbS2 both interstitial and substitutional dopings can coexist depending upon the particular synthesis conditions. The analysis of the structural and electronic modifications of the perfect bulk systems due to the doping is presented. We show that substitutional Nb atoms introduce electron holes to the MoS2 leading to a semiconductor-metal transition. On the other hand, the Mo doping of NbS2 does not alter the metallic behavior of the initial system. The results of the present study are compared with available experimental data on mixed MoS2-NbS2 (bulk and nanoparticles).