Reactive Solid-Phase Epitaxial Growth of Na x CoO 2 ( x ∼ 0.83) via Lateral Diffusion of Na into a Cobalt Oxide Epitaxial Layer

High-quality epitaxial films of layered cobaltite Na 0.83 CoO 2 were successfully grown on (0001)-oriented α-Al 2 O 3 substrate by reactive solid-phase epitaxy using CoO epitaxial layer and NaHCO 3 powder. First, the thermal oxidation of the CoO film into Co 3 O 4 occurs at a lower temperature (300−500 °C), then a Na 0.83 CoO 2 epitaxial layer formed via lateral diffusion of Na + ions together with oxide ions into Co 3 O 4 layers.