Spectroscopic comprehension of Mott-Hubbard insulator to negative charge transfer metal transition in LaNixV1-xO3 thin films

The room-temperature (300 K) electronic structure of pulsed laser deposited LaNixV1-xO3 thin films has been demonstrated. The substitution of early-transition metal (TM) V in LaVO3 thin films with late-TM Ni leads to the decreasing in out-of-plane lattice parameter. Doping of Ni does not alter the formal valence state of Ni and V in LaNixV1-xO3 thin films, divulging the absence of carrier doping into the system. The valence-band spectrum is observed to comprise incoherent structure owing to the localized V 3d band along with the coherent structure at Fermi level. With increase in Ni concentration, the weight of the coherent feature increases, which divulges its origin to the Ni 3d-O 2p hybridized band. The shift of Ni 3d-O 2p hybridized band towards higher energy in Ni-doped LaVO3 films compared to the LaNiO3 film endorses the modification in ligand to metal charge transfer (CT) energy. The Ni doping in Mott-Hubbard insulator LaVO3 leads to the closure of the Mott-Hubbard gap by building of spectral weight that provides the delocalized electrons for conduction. A transition from bandwidth control Mott-Hubbard insulator LaVO3 to negative CT metallic character in LaNiO3 film is observed. The study reveals that unlike in Mott-Hubbard insulators, where the strong Coulomb interaction between the 3d electrons decides the electronic structure of the system, CT energy can deliver an additional degree of freedom to optimize material properties in Ni-doped LaVO3 films.