Abstract
Two new compounds of the Bi/Ca/Co/O and Bi(Pb)/Ca/Co/Osystems have been prepared. Their structure is built up fromthe 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, at2.5 K, − 85%in 7 T for the Bi/Ca/Co/O misfit cobaltite. A large negative magnetothermopower isalso found for these cobaltites in the same temperature range. A qualitativeexplanation of the observed behaviour is proposed.
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