ANISOTROPIC BAND PROPERTIES OF THE LINEAR-CHAIN NICKELATE Y2BANIO5

The nonmagnetic band structure of Y2BaNiO5, an orthorhombic nickelate that contains one-dimensional (ID) chains of vertex-linked NiO6 octahedra, has been calculated in the local-density approximation with the use of the linear augmented-plane-wave method. Neglecting magnetic effects, the results imply metallic behavior that originates from partially filled Ni(3d) conduction bands with e(g) character. This e(g) manifold is composite in nature, featuring a relatively narrow (approximately 0.3 eV) delta*-type level amid a broader (approximately 2 eV) sigma* subband with well-defined ID characteristics. At half filling, for example, the components of the sigma*-band Fermi-velocity squared [upsilon(F)2] perpendicular to the chain axis are only approximately 1-2% of the corresponding parallel value. Although antiferromagnetism is expected to induce insulating behavior in this system, the present results may be relevant in doped systems if magnetism can be suppressed.