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To investigate the relationship between the electronic structure and the power factor of Na_xCoO_2(x=0.3,0.5 and 1.0),the first-principles calculation is conducted by using density functional theory and the semi-classical Boltzmann theory.Our results suggest that with the decreasing Na content,a transition from semiconductor to semimetal is observed.Na_(0.3)CoO_2 possesses a higher electrical conductivity at 1000 K due to its increased density of states near the Fermi energy level.However,an optimal Seebeck coefficient at 1000 K is obtained in Na_(0.5)CoO_2 because of its broadened band gap near the Fermi energy level.Consequently,a maximum power factor is realized in Na_(0.5)CoO_2.Thus our work provides a complete understanding of the relationship between the electronic structure and the thermoelectric power factor of Na_xCoO_2.
To investigate the relationship between the electronic structure and the power factor of Na_xCoO_2 (x = 0.3, 0.5 and 1.0), the first-principles calculation is conducted by using density functional theory and the semi-classical Boltzmann theory. Our results suggest that with the Na Na (0.3) CoO_2 possesses a higher electrical conductivity at 1000 K due to its increased density of states near the Fermi energy level. However, an optimal Seebeck coefficient at 1000 K is obtained in Na_ (0.5) CoO_2 because of its broadened band gap near the Fermi energy level. Reconstructed, a maximum power factor is realized in Na_ (0.5) CoO_2.Thus our work provides a complete understanding of the relationship between the electronic structure and the thermoelectric power factor of Na_xCoO_2.