Fig. 2

Diffusion path of H for the Si < = > 4H defect at 2500 K. Mg, Si, O, and H are represented respectively by pink, yellow, red, and white spheres. Sphere radii not to scale. The trajectory of the H atoms is shown with the dotted line over several picoseconds. a shows only the H trajectory for clarity. The diffusion path is shown in the context of the entire structure in (b) and (c). The hydrogen atoms occupy the Si vacancy. After escape, indicated by the white arrow, one of them described donut shapes while trapped in an empty octahedron, before falling into the neighboring Si vacancy and thus realizing a net proton transfer (a). The diffusion path describes channel-like patterns along the z-axis, as viewed in the image along x-axis (b) and z-axis (c). The unit cell is outlined with dashed line