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 octahe dra, has been calculated in the local-density approximation with the u se of the linear augmented-plane-wave method. Neglecting magnetic effe cts, the results imply metallic behavior that originates from partiall y filled Ni(3d) conduction bands with e(g) character. This e(g) manifo ld is composite in nature, featuring a relatively narrow (approximatel y 0.3 eV) delta-type level amid a broader (approximately 2 eV) sigma* subband with well-defined ID characteristics. At half filling, for ex ample, the components of the sigma-band Fermi-velocity squared [upsil on(F)2] perpendicular to the chain axis are only approximately 1-2% of the corresponding parallel value. Although antiferromagnetism is expe cted to induce insulating behavior in this system, the present results may be relevant in doped systems if magnetism can be suppressed.