Effect of microstructure on the electric properties of NaCo₂O₄ ceramics

NaCo₂O₄ polycrystalline powders were synthesized by self-flux method, and then ceramic samples were prepared by two methods of uniaxial pressing and cold isostatic pressing. Phases and micro-morphology analysis as well as its electric properties were observed. The impacts of grain preferred orientation and relative density of NaCo₂O₄ ceramics on electric properties were investigated accordingly. As a result, a higher electrical conductivity and power factor of sample are caused by its higher preferred orientation degree and relative density. The sample of Na∶ Co=0.7∶1 with uniaxial pressure is proved to have a higher preferred orientation degree and relative density comparatively. Meanwhile, it can be observed that electrical conductivity reaches to a maximum value of 4.2×10⁴ S·m^-1 at 303 K, and a maximum value of power factor equals to 450μ W·m^-1·K^-2 at 823 K.