Annealing environment dependent electrical and chemical state correlation of Li-doped NiO

The effects of annealing environments and dopants on the structural, chemical, optical, and electrical properties of NiO are investigated. Pristine NiO exhibits electrically insulating behavior regardless of the annealing environments (e.g., vacuum and O2 environments). On the other hand, Li-doped NiO exhibits electrical resistivities of ∼350 Ω cm and ∼9 Ω cm for the ceramics annealed under vacuum and O2, respectively with reduced optical band-gap. The structural analysis revealed that all the samples exhibit a cubic structure (Fm-3m, SG 225) without any measurable secondary phases. However, Li-doped NiO samples showed a reduction in the unit cell volume as compared to the undoped NiO samples. X-ray photoelectron spectroscopy revealed different residual Li content depending on the annealing environments, and the presence of induced Ni3+ state in the Li-doped NiO. These induced Ni3+ states and doped Li are responsible for the observed change in the structural and electrical properties of the Li-doped NiO samples. •Li doping can reduce electrical resistivity and unit cell volume.•Annealing under O2 environment allowed to dope more Li in the host lattice rather than vacuum annealing.•Substituting Li+ ions at Ni2+ sites can induce Ni3+ ions by oxidation process owing to the charge compensation.•Decrease in the electrical resistivity with Li doping may be related to the Ni3+-induced acceptor level.