Abstract
We report a simple approach of fabricating thermoelectric gamma-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 gamma-Na0.68CoO2 film grown by the reactive solid-phase epitaxy. The fitted thermopower data show that the bandwidth of gamma-NaxCoO2 is found to be similar to 101 meV, being close to the quasi-particle band (70-100 meV) derived from an angle-resolved photoemission study of gamma-Na0.7CoO2. These results enable the possibility of low-cost fabrication of gamma-NaxCoO2-based thermoelectric film devices. Furthermore, we have also topotactically transformed the of gamma-NaxCoO2 film to a superconducting Na-x(H2O)(y)CoO2-delta film with T-c,T- (onset) = 4.12 K. (C) 2009 Elsevier B.V. All rights reserved.