Enhanced thermoelectric properties of NaCo2O4 by adding ZnO

The primary phase present in the as-sintered Na(Co(1-x)Zn(x))(2)O(4) (0 <= x <= 0.1) bodies was the solid solution of the constituent oxides with a bronze-type layered structure. The electrical conductivity of the Na(Co(1-x)Zn(x))(2)O(4) samples significantly increased with an increase in ZnO content. The sign of the Seebeck coefficient for all samples was positive over the whole temperature range (723-1073 K), i.e., p-type conduction. The power factor of Na(Co(0.95)Zn(0.05))(2)O(4) showed an outstanding power factor (1.7 x 10(-3)Wm(-1) K(-2)) at 1073 K. The power factor was above four times superior to that of ZnO-frec NaCo(2)O(4) (0.4 x 10(-3)Wm(-1) K(-2)). This originates from an unusually large Seebeck coefficient (415 mu VK(-1)) accompanied with high conductivity (127 Omega(-1) cm(-1)) at 1073 K. (C) 2007 Elsevier B.V. All rights reserved.