We report a simple approach of fabricating thermoelectric γ-NaxCoO2 film with the c-axis orientation using the sol–gel spin-coating method. The inferred sodium content is x = 0.65 according to the correlation between the c-axis lattice constant and x. Temperature dependence of both the resistivity and thermopower resembles that of the γ-Na0.68CoO2 film grown by the reactive solid-phase epitaxy. The fitted thermopower data show that the bandwidth of γ-NaxCoO2 is found to be ~ 101 meV, being close to the quasi-particle band (70–100 meV) derived from an angle-resolved photoemission study of γ-Na0.7CoO2. These results enable the possibility of low-cost fabrication of γ-NaxCoO2-based thermoelectric film devices. Furthermore, we have also topotactically transformed the of γ-NaxCoO2 film to a superconducting Nax(H2O)yCoO2-δ film with Tc, onset = 4.12 K.
