Abstract
The detailed crystal structures and high temperature thermoelectric properties of polycrystalline Ca3−2xNa2xCo4−xWxO9 (0 ≤ x
≤ 0.075) samples have been investigated. Powder X-ray diffraction data
show that all samples are phase pure, with no detectable traces of
impurity. The diffraction peaks shift to lower angle values with
increase in doping (x), which is consistent with larger ionic radii of Na+ and W6+ ions. X-ray photoelectron spectroscopy data reveal that a mixture of Co2+, Co3+ and Co4+ valence states are present in all samples. It has been observed that electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ) are all improved with dual doping of Na and W in Ca3Co4O9 system. A maximum power factor (PF) of 2.71 × 10−4 W m−1 K−2 has been obtained for x = 0.025 sample at 1000 K. The corresponding thermoelectric figure of merit (zT) for x = 0.025 sample is calculated to be 0.21 at 1000 K, which is ∼2.3 times higher than zT
value of the undoped sample. These results suggest that Na and W dual
doping is a promising approach for improving thermoelectric properties
of Ca3Co4O9 system.
Original language | English |
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Journal | R S C Advances |
Volume | 8 |
Issue number | 22 |
Pages (from-to) | 12211–12221 |
ISSN | 2046-2069 |
DOIs | |
Publication status | Published - 2018 |