The electronic structure of various nickel oxides with nickel valence varyi
ng from 1+ to 3+ was investigated with the aim to find similarities and dif
ferences to the isoelectronic cuprates. Only if the Ni ions are forced into
a planar coordination with the O ions can a S = 1/2 magnetic insulator be
realized with the difficult Ni+ oxidation state and possibly doped with low
spin (S = 0) Ni2+ holes directly analogous to the superconducting cuprates
. The more common Ni3+ oxidation state cannot be used to make a parent magn
etic insulator as it forms rather as localized S = 1 Ni2+ embedded in a sea
of itinerant O holes. Strong coupling of these holes to the localized spin
s via 2p-3d hybridization leads to a heavy-fermion system with a large Kond
o temperature, which was confirmed experimentally for LaNiO3. [S0163-1829(9
9)03411-6].