Oriented thin films of Na _0.6CoO ₂ and Ca ₃Co ₄O ₉ deposited by spin-coating method on polycrystalline substrate

Thin film of two thermoelectric materials, Na _xCoO ₂ (x ~ 0.6) and Ca ₃Co ₄O ₉, was deposited using the sol–gel spin-coating method on a polycrystalline yttria-stabilized zirconia (YSZ) substrate. Despite the polycrystalline character of the substrate, the c-axis preferred orientation was obtained, suggesting self-assembly growth mechanism. The deposition procedure used offers several benefits, namely simplicity, high deposition rate, low fabrication cost as well as low price of the substrate, and low thermal conductivity of the substrate suitable for characterization of thermoelectric properties and for applications. The thermoelectric properties of the thin films are comparable with bulk materials. The samples exhibit power factor 0.23 - 0.26 × 10^-3 W ⋅ m ^-1 ⋅ K ^-2 at 750 K. - Highlights: • Thin film of thermoelectric cobaltates was deposited using the spincoating method. • The c-axis preferred orientation was obtained on polycrystalline YSZ substrate. • Benefits of the chosen procedure are simplicity, low cost, and low thermal conductivity of the substrate.