ELECTRONIC-STRUCTURE AND STABILITY OF PERIODICALLY REPEATED CU(CA0.3SR0.7)(2)(CA0.3SR0.7)(N-1)CUNO2N-DELTA DEFECT LAYERS IN INFINITE-LAYER SUPERCONDUCTORS(2)

Based on an analysis of high-resolution electron microscope images, Ta o and Nissen have recently proposed a class of structural units involv ing partially occupied apical oxygen sites to model the defect layers occurring in superconducting infinite-layer compounds. In this work we study the stability of the smallest of these structural units by mini mizing the total energy with respect to the cell parameters and intern al atomic coordinates, using the full-potential augmented plane wave ( FLAPW) method. To investigate the proposed coexistence of both n and p type doping according to the O content or to the number n of CuO2 pla nes, we study the electronic structure of this system, of an O deficie nt supercell and of the n = 2 structure. We find that even for a nomin al electron doping, the charge carriers in the system are hole-like.