Panoply of Ni-Doping-Induced Reconstructions, Electronic Phases, and Ferroelectricity in 1T-MoS₂

The distorted phases of monolayer 1T-MoS2 have distinct electronic properties, with potential applications in optoelectronics, catalysis, and batteries. We theoretically investigate the use of Ni-doping to generate distorted 1T phases and find not only the ones usually reported but also two further phases (3 × 3 and 4 × 4), depending on the concentration and the substitutional or adatom doping site. Corresponding pristine phases are stable after removal of dopants, which might offer a potential route to experimental synthesis. We find large ferroelectric polarizations, most notably in 3 × 3 which─compared to the recently measured 1T″─has 100 times greater ferroelectric polarization, a lower energy, and a larger band gap. Doped phases include exotic multiferroic semimetals, ferromagnetic polar metals, and improper ferroelectrics with only in-plane polarization switchable. The pristine phases have unusual multiple gaps in the conduction bands with possible applications for intermediate band solar cells, transparent conductors, and nonlinear optics.