Electronic structure of possible nickelate analogs to the cuprates

The electronic structure of various nickel oxides with nickel valence varying from 1+ to 3+ was investigated with the aim to find similarities and differences 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 magnetic 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 spins via 2p-3d hybridization leads to a heavy-fermion system with a large Kondo temperature, which was confirmed experimentally for LaNiO3. [S0163-1829(99)03411-6].