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Abstract:
The electron density distribution of the nickel compounds BaNiO2, BaNiO3
and CaNiN has been investigated experimentally by Ni-61 Mossbauer
spectroscopy and theoretically by band structure calculations using the
FP-LMTO (Full Potential Linear Muffin-Tin Orbital) method. For all
compounds good agreement is found between the experimental and
theoretical values of the electric field gradient q(exp.) and q(theor.)
at the nickel site.
BaNiO2 contains nickel in a square-planar coordination forming puckered
chains of edge-sharing NiO4 squares. \q\ at nickel is large: q(exp.) =
-15.7(1.5) . 10(21) Vm(-2) and q(theor.) = -15.59 . 10(21) V-m-2.
The principal axis z is perpendicular to the NiO, squares. The crystal
structure of BaNiO, contains face-sharing chains of NiO6 octahedra. In
BaNiO3 q(Ni) is small: q(exp) = +/- 3.6 (2.0) . 10(21) Vm(-2) and
q(theor.) = - 1.86 . 10(21) Vm(-2). Because of the small broadening of
the Mossbauer resonance line the sign of q could not be determined
experimentally.
The nitridoniccolate CaNiN contains infinite linear chains
The nitridoniccolate CaNiN contains infinite linear chains 1 over
infinity [NiN2/2] which run perpendicular to the c axis. Unexpectedly,
\q(Ni)/ in CaNiN is small: q(exp.)=0.0(2.0). 10(21)Vm(-2) and
q(theor.)=-3.05 . 10(21)Vm(-2). Again the sign q(Ni) could not be
determined experimentally. It is found theoretically that the small
value of q(Ni) is caused by severe cancellation between sigma and pi
contributions.
[NiN2/2] which run perpendicular to the c axis. Unexpectedly, \q(Ni)\ in
CaNiN is small: q(exp) = 0.0 (2.0) . 10(21) Vm(-2) and q(theor.) = -3.05
. 10(21) Vm(-2). Again the sign of q(Ni) could not be determined
experimentally. It is found theoretically that the small value of q (Ni)
is caused by severe cancellation between sigma and pi contributions.
