The process of formation of surface structures in a paratellurite crystal (α-TeO₂) in an external electric field has been studied by in situ X-ray diffraction (XRD) measurements. This process is reversible and its dynamics (duration of tens of minutes) corresponds to the formation of a screening layer near the insulator–metal interface owing to the counter migration of oxygen ions and vacancies in the external electric field. The formation of domains has been observed in the experiment as the broadening and splitting of the XRD curve and is explained by mechanical stresses that appear in the high electric field near the surface in view of the piezoelectric effect and are responsible for a ferroelectric α–β phase transition. A change in the lattice parameter near the anode (surface of the crystal with a positive external charge) has been detected simultaneously. This change is due to the local rearrangement of the crystal structure because of the inflow of oxygen ions in this region and outflow of oxygen vacancies.