Spectroscopic comprehension of Mott-Hubbard insulator to negative charge transfer metal transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>La</mml:mi><mml:msub><mml:mi>Ni</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mi mathvariant="normal">V</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> thin films
Anupam Jana, Sophia Sahoo, Sourav Chowdhury, Arup Kumar Mandal, Santosh Bimli, Rupesh S. Devan, R. J. Choudhary, D. M. Phase, A. K. Raychaudhuri
Abstract
The room-temperature (300 K) electronic structure of pulsed laser deposited $\mathrm{La}{\mathrm{Ni}}_{x}{\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{O}}_{3}$ thin films has been demonstrated. The substitution of early-transition metal (TM) V in $\mathrm{LaV}{\mathrm{O}}_{3}$ 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 $\mathrm{La}{\mathrm{Ni}}_{x}{\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{O}}_{3}$ 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 $3d\text{\ensuremath{-}}\mathrm{O} 2p$ hybridized band. The shift of Ni $3d\text{\ensuremath{-}}\mathrm{O} 2p$ hybridized band towards higher energy in Ni-doped $\mathrm{LaV}{\mathrm{O}}_{3}$ films compared to the $\mathrm{LaNi}{\mathrm{O}}_{3}$ film endorses the modification in ligand to metal charge transfer (CT) energy. The Ni doping in Mott-Hubbard insulator $\mathrm{LaV}{\mathrm{O}}_{3}$ 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 $\mathrm{LaV}{\mathrm{O}}_{3}$ to negative CT metallic character in $\mathrm{LaNi}{\mathrm{O}}_{3}$ 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 $\mathrm{LaV}{\mathrm{O}}_{3}$ films.