No abstract

Role of theA-site size and oxygen stoichiometry in charge ordering commensurability of Ln 0.50 Ca 0.50 MnO 3 manganites J. Appl. Phys. 84, 5506 (1998); 10.1063/1.368313Cation size-temperature phase diagram of the manganites Ln0.5Sr0.5MnO3

Two new compounds of the Bi/Ca/Co/O and Bi(Pb)/Ca/Co/O systems have been prepared. Their structure is built up from the intergrowth of four rock-salt-type layers and one [CoO2 ] hexagonal layer. Both cobaltites exhibit large thermopower values (S300 K ∼ 140 µV K−1), low resistivity values (ρ300 K = 40–60 mΩ cm) and small thermal conductivities (κ300 K ∼ 1 W K−1 m−1). Furthermore, these compounds exhibit a negative magnetoresistance, (MR = ρH − ρH = 0/ρH = 0), reaching, at 2.5 K, − 85% in 7 T for the Bi/Ca/Co/O misfit cobaltite. A large negative magnetothermopower is also found for these cobaltites in the same temperature range. A qualitative explanation of the observed behaviour is proposed.