CHARGE-DENSITY DISTRIBUTION IN ALKALINE-EARTH CUPRATES WITH ONE-DIMENSIONAL OR 2-DIMENSIONAL ARRANGEMENTS OF CU-O

We report the charge density distribution rho(r) ( = \phi(r)\(2); phi( r) wave function) of Ca2CuO3 with the one-dimensional Cu-O chain and ( Sr0.15Ca0.85)CuO2 with the two-dimensional CuO2 plane, in comparison w ith that of superconducting YBa2Cu3O6.9 with both the Cu-O atomic arra ngements. rho(r) was obtained by the Maximum-Entropy Method (MEM) anal ysis using laboratory X-ray powder diffraction data. The rho(r) in (Ca ,Sr)CuO2 is almost spherical, indicating that ionic features are domin ant in the CuO2 planes. This contrasts with the case of superconductin g YBa2Cu3O6.9, which shows remarkable overlapping between Cu 3d and O 2p orbitals. On the contrary, the rho(r) in Ca2CuO3 indicates substant ial overlapping between Cu and O only along the single chain direction and no interaction between each Cu-O chain.