Figure 1. Atomic structures of the various structures of hydrogen at an O-site in ZnO: (a) H_O, (b) H-DX, and (c) H-DX*.

The (red)-dashed arrow lines in (b) and (c) indicate the direction of H-displacement for the formations of H-DX⁻ structures. (c) H-DX* is a meta-stable structure. The open circles describe V_O⁰ site in the H-DX⁻ which is a complex defect of H_i⁻ and V_O⁰.