Studies on solid state reactions of atomic layer deposited thin films of lithium carbonate with hafnia and zirconia

In this paper, results on the solid state reactions of atomic layer deposited Li₂CO₃ with HfO₂ and ZrO₂ are reported. An Li₂CO₃ film was deposited on top of hafnia and zirconia, and the stacks were annealed at various temperatures in air to remove the carbonate and facilitate lithium diffusion into the oxides. It was found that Li⁺ ions are mobile in hafnia and zirconia at high temperatures, diffusing to the film–substrate interface and forming silicates with the Si substrate during heating. Based on grazing incidence x-ray diffraction experiments, no changes in the oxide phases take place during this process. Field emission scanning electron microscopy images reveal that some surface defects are formed on the transition metal oxide surfaces during lithium diffusion. The authors also show that lithium can diffuse through hafnia and react with a potential lithium-ion battery electrode material TiO₂ residing below the HfO₂ layer, forming Li₂TiO₃.