Ab-initio Band Structure Calculations and ⁶¹ Ni-Mössbauer Studies of BaNiO₂ , BaNiO₃ and CaNiN

Abstract

The electron density distribution of the nickel compounds BaNiOBaNiOThe principal axis z is perpendicular to the NiOThe nitridoniccolate CaNiN contains infinite linear chains

Charge and dimensionality effects on the properties of CaNiN

“…The electron density of the latter is spread out over the complete system-i.e., also between the NiN chain and the Ca atoms-which is a clear indication of covalency. A similar result can be seen in the electron-density plots for crystalline CaNiN of Hannebauer et al 5 Qualitative, but only partly quantitative, estimates of atomic charges, electron transfers, and covalent interactions can be obtained from the number of electrons inside the atomic spheres and the Löwdin and Mulliken populations. These are presented in Table I.…”

“…Thus, Hannebauer et al 5 find the deepest band between about −14.7 and −13.5 eV and the upper features above around −6.7 eV. The calculations of Massidda et al 3 give that the upper feature starts at −6.5 eV and the Van Hovelike feature appears at −4.3 eV, and also Mattheiss 4 finds that the broadband saround the Fermi level start at around −6.5 eV.…”

“…He was especially interested in comparisons between this material and the high-T c cuprate superconductors, since both systems have negatively charged 2D layers separated by positively charged ions. Finally, Hannebauer et al 5 compared the band structures, the total electron density, and Ni Mössbauer parameters of BaNiO 2 , BaNiO 3 , and CaNiN. The Mössbauer parameters were compared with their own experimental results.…”

“…Although the studies of Massidda et al, 3 Mattheiss, 4 and Hannebauer et al 5 were very useful, a number of issues were not completely resolved. For example, when discussing superconductivity, it is crucial to have an accurate description of the density of states (DOS) around the Fermi level.…”

Electronic State of Nickel in Barium Nickel Oxide, BaNiO3

“…This quadrupole splitting is observed when the electric field gradient (efg) which is controlled by valence and lattice contributions is unequal to zero at the nucleus. The quadrupole splitting measured for BaNiO 2 corresponds to V zz = −1.5 × 10 18 V cm -2 and belongs thus to the highest values measured so far for nickel compounds . In contrast with the 4-fold coordination of nickel by oxygen in BaNiO 2 the octahedral ligand field of Ni 4+ in BaNiO 3 is not expected to result in quadrupole splitting.…”