Fabrication of lithium-doped zinc oxide film by anodic oxidation and its ferroelectric behavior

A lithium-doped zinc oxide (ZnO) film was obtained by the anodic oxidation of a zinc sheet in a lithium hydroxide (LiOH) solution under an external DC voltage. The formation of the ZnO film on the surface of the Zn sheet is attributed to two simultaneous processes: the electrochemical oxidation of Zn to ZnO, and the chemical dissolution of ZnO. It was also confirmed that Li element was successfully introduced into the lattice of the ZnO film. The curves of the polarization versus applied field were measured to be hysteresis loops, suggesting ferroelectricity of the Li-doped ZnO film. The remanent polarization and the coercive field of the film were measured to be 4.7 × 10 −3 C m −2 and 1.2 × 10 7 V m −1, respectively. This ferroelectricity is believed to be the result of the occupation of off-centered positions in oxygen tetrahedra by the Li + ions.