Phase stability and Raman/IR signatures of Ni-doped MoS₂ from DFT studies

Doping MoS₂ with Ni is known to enhance lubrication and catalysis. While much of the experiment and theory regarding doped MoS₂ has focused mostly on monolayers or finite particles, theoretical studies of bulk Ni-doped MoS₂ are lacking and the mechanisms by which Ni alters bulk properties are largely unsettled. We use density functional theory calculations to determine the structure, mechanical properties, electronic properties, and formation energies of bulk Ni-doped MoS₂ while varying the doping concentration. We find four meta-stable structures of Ni-doped MoS₂: Mo or S substitution, and tetrahedral (t-site) or octahedral (o-site) intercalation. To aid in experimental identification, we calculate the infrared and Raman spectra and identify the features unique to each dopant site. We compute formation energies of these structures with respect to chemical potentials to guide experimental synthesis and we find the t-site structure to be particularly stable. Intercalation forms strong interlayer covalent bonds and does not increase the c-parameter. Doping creates new states present in the electronic density of states in MoS₂ and shifts the Fermi level. These results are being used to parametrize force fields for study of Mo₂ friction. arXiv: 2010.02198