Microstructural, Thermoelectric and Mechanical Properties of Cu Substituted NaCo2O4

Polycrystalline samples of NaCo2-xCuxO4 (x = 0, 0.01, 0.03, 0.05) were obtained from powder precursors synthesized by a mechanochemically assisted solid-state reaction method (MASSR) and a citric acid complex method (CAC). Ceramic samples were prepared by pressing into disc-shaped pellets and subsequently sintering at 880 degrees C in an argon atmosphere. Effects of low concentrations of Cu doping and the above-mentioned synthesis procedures on the thermoelectric and mechanical properties were observed. The electrical resistivity (rho), the thermal conductivity (kappa) and the Seebeck coefficient (S) were measured simultaneously in the temperature gradient (Delta T) between the hot and cold side of the sample, and the figure of merit (ZT) was subsequently calculated. The ZT of the CAC samples was higher compared with the MASSR samples. The highest ZT value of 0.061 at Delta T = 473 K was obtained for the sample with 5 mol% of Cu prepared by the CAC method. The CAC samples showed better mechanical properties compared to the MASSR samples due to the higher hardness of the CAC samples which is a consequence of homogeneous microstructure and higher density obtained during sintering of these samples. The results confirmed that, besides the concentration of Cu, the synthesis procedure considerably affected the thermoelectric and mechanical properties of NaCo2O4 (NCO) ceramics.

Automated summary

The thermoelectric and mechanical properties of NaCo2O4 ceramics were significantly affected by the synthesis procedure and Cu doping concentration. Samples prepared by the citric acid complex method showed higher thermoelectric performance and mechanical properties.