BONDING PATTERNS AND INSTABILITIES IN THE M=2 RUDDLESDEN-POPPER PHASES - LASR2MN2O7 AND LA2CACU2O6

We present the results of high level band structure calculations on th e important layered compounds LaSr2Mn2O7 and La2CaCu2O6; both of which have the structure of the m = 2 member of the Ruddlesden-Popper phase s and comprise intergrowths of double perovskite slabs with rock-salt slabs. The cuprate additionally has an ordered oxygen defect. For furt her comparison, the band structure of tetragonal La2CuO4 has also been calculated. The manganite is a material exhibiting giant magnetoresis tance (GMR) effects and the cuprates can be doped to give superconduct ors. The calculations have been performed using the TB-LMTO-ASA progra ms within the local (spin) density approximation L(S)DA; for the manga nite, spin-polarized calculations result in a magnetic ground state; c alculations on the ferromagnet and two antiferromagnetic structures ar e compared. The calculations show up similarities and differences betw een the bonding patterns of these two structurally related compounds t hat display widely different ground states when they are doped. The in stabilities on or near the Fermi surface possibly implicated in the st abilization of the different ground states are, however, quite similar in character.