The effect of synthesis technique on thermoelectric properties of nanocrystalline NaCo2O4 ceramics

Sodium cobalt oxide (NaCo2O4) nanocrystalline thermoelectric ceramic powders were synthesized using conventional polymerized complex sol–gel and electrospinning techniques and then consolidated into bulk ceramics. We have investigated the differences in the microstructure and thermoelectric properties of the samples prepared using electrospinning and sol–gel methods. The crystal structures of the powders and nanofibers were characterized using X-ray diffraction and scanning electron microscopy before and after calcination at different temperatures. Nanofibers prepared by electrospinning have a diameter of approximately 300 nm, while the diameter of the grains of sol–gel powders ranges from 1 to 5 µm. Thermoelectric properties of the bulk ceramics were measured by physical properties measurement system in the temperature range of 15–300 K. The calculated values of dimensionless figure of merit at 300 K are 6 × 10−7 and 4 × 10−5 for sintered powders from sol–gel and nanofibers, respectively. While electrospinning production technique increase thermoelectric power approximately 15 % and it fold electrical conductivity average 20 times, it decreased thermal conductivity by 90 %.