Highly textured NaxCoO2-δ ceramics fabricated by both templated grain growth and reactive templated grain growth methods using single-crystalline particles as templates

Textured gamma-NaxCoO2-delta ceramics have been prepared by both templated grain growth (TGG) and reactive templated grain growth (RTGG) methods using single-crystalline particles of gamma-NaCoO2-delta as templates. An XRD analysis indicated that the samples were highly c-axis oriented; i.e., the highest Lotgering's factor was estimated to be 0.93. According to transport property measurements, the highly textured gamma-NaxCoO2-delta sample exhibited electrical conductivity (sigma) = similar to1.85 x 10(4) S/m, Seebeck, coefficient (S) = similar to137 muV/K and power factor (PF = sigma.S-2) =0.35 mW.m(-1).K-2 at similar to800 K. These values of sigma and S are smaller than those of single crystals (sc); that is, sigma(sc) = 19.2 x 10(4) S/m and S-sc = 200 muV/K at 800 K. The magnitude of sigma was found to decrease in proportion to the relative density (d) of the sample, while S was independent of d. Furthermore, both sigma and S seemed to be sensitive to the Na content of the samples. Both the low density (dsimilar to70%) and the deviation from the optimal Na content were considered to be predominant factors for the low thermoelectric properties of the present textured samples.