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).