THE 1201 BISMUTH-BASED COBALTITE BI0.5CD0.3SR2CO1.2O5-DELTA - A NEW MAGNETORESISTANT SPIN-GLASS-LIKE INSULATOR

A new ''1201'' bismuth based cobaltite, Bi0.5Cd0.3Sr2Co1.2O5-delta, ha s been synthesized. Its single crystal structure determination shows t hat this tetragonal phase [a = 3.7765(1) Angstrom, c = 8.7812(3) Angst rom] exhibits regular single perovskite layers [SrCoO3](infinity) char acterized by an elongation of the CoO6 octahedra, whereas the rock sal t layers [Bi0.5Cd0.3Co0.2SrO2-delta](infinity) exhibits disordered phe nomena especially concerning the distribution of the metallic species and splitting of the oxygen positions in the intermediate layer [(Bi, Cd, Co)O]. The most important feature of this oxide deals with its spi n glass like behavior (T-cusp = 49 K) and negative magnetoresistance p roperties (MR% = 23% at 70 K). The latter are interpreted in terms of competition between double-exchange (Co3+-Co4+ ferromagnetic interacti ons) and superexchange (Co3+-Co3+ and Co4+-Co4+ antiferromagnetic inte ractions). (C) 1998 Elsevier Science Ltd.