Orientation alignment of epitaxial LiCoO₂ thin films on vicinal SrTiO₃ (100) substrates

LiCoO₂ is epitaxially grown on SrTiO₃ (100) substrates with (104) orientation. Because the LiCoO₂ film is grown with its c-axis parallel to four equivalent 〈111〉 axes of the SrTiO₃, the (104)-oriented film exhibits four-domain structure on the SrTiO₃ (100) substrate. Introducing off-cut angle to the substrate surface breaks the equivalency between the four 〈111〉 axes of the SrTiO₃ substrate to induce preferential growth of specific orientation with the c-axis in a descending direction of off-cut surface. Increasing off-cut angle and lowering deposition rate promote the preferential growth, because they facilitate step-flow growth mode, and finally align the c-axes in the domains completely into one 〈111〉 direction of the SrTiO₃ substrate. The LiCoO₂ film delivers a discharge capacity of 90 mAh g⁻¹ at a low discharge rate of 0.01 C, and 25% of capacity is kept even at a high rate of discharge with 100 C.