Fabrication and thermoelectric properties of Na_{xCoO_{2 by polymerised complex method

Determination of thermoelectric properties of NaxCoO2 (x = 0.5, 0.6, 0.7, 0.8, 0.85, and 0.9) fabricated by polymerised complex (PC) method has been investigated in the temperature range 300-773 K. The single phase of NaxCoO2 was identified in samples with higher Na concentration (x > 0.7), while the second phase of Co3O4 was detected in that of lower Na concentration. The data from the measurement of Seebeck coefficients of all the samples suggest that they are p-type, which means that the major carrier concentrations are holes. The lowest electrical resistivity was obtained from sample x = 0.8. A fine microstructure was observed and is due to the PC method of fabrication, leading to low thermal conductivity. The maximum dimensionless figure of merit (ZT) of 0.25 at 773 K was evident in sample x = 0.8, which was mainly due to its lower electrical resistivity.