Anisotropy and kinetics of the migration-induced layer formation in TeO2

The dynamics and anisotropy of the formation processes of near-surface structures in paratellurite (α-TeO2) single crystals due to the migration of charge carriers induced by an external electric field are studied by x-ray diffraction and electrophysical methods. Significant yet reversible variations in the parameters of the diffraction rocking curves are observed. A diffraction peak broadening occurs for both polarities with a simultaneous shift of its maximum only occurring on the surface with a positive electric potential. For the [100] direction, a much higher velocity of saturation and relaxation processes was registered compared to the [110] direction. Moreover, a significant increase in the integral intensity of the 200 diffraction peak was observed. The electric field application along the fourth-order axis [001] does not lead to visible changes in the diffraction peak parameters. The dynamics and amplitude of the diffraction peak variation reflect the structural changes in the thin near-surface region of the crystal volume. This corresponds to the measured kinetics and value of the electric conductivity and the formation of the electrical double layer close to the insulator–metal interface, which is attributed to the oxide ion migration process from the crystal volume to its surfaces. The thickness of the structure formed close to the surface is estimated by mathematical calculations (the Debye screening length) and by x-ray diffraction (a layer with mechanical deformations) obtained at different diffraction orders. The experimental data are compared with the results of the x-ray diffraction peak simulations considering the crystal lattice strain with the depth attenuation.