Abstract
The effects of Ir doping on the low-temperature thermal and electrical transport properties of Ca3Co4−xIrxO9 (0 ≤ x ≤ 0.4) have been investigated. As Ir ions are doped into the system, a low-temperature thermopower upturn is introduced, and the temperature corresponding to the minimum thermopower TSmin increases monotonously with increasing x. Moreover, a low-temperature colossal thermopower is observed in the Ir-doped samples, which is beneficial to the low-temperature thermoelectric refrigeration in superconducting devices. For the x = 0.4 sample, its maximum thermopower Smax at the lowest measured temperature ∼24 K reaches 1500 μV/K. The appearance of such a colossal thermopower phenomenon is suggested to be closely related to the variations of the transport mechanism and the band structure induced by 5d-Ir doping.
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