Fast near-surface changes in the defect structure in lithium tetraborate crystals in an external electric field

The changes in the defect structure in the near-surface layers of lithium tetraborate (Li$_{2}$B$_{4}$O$_{7}$) single crystals under the influence of an external electric field applied along the polar direction [001] have been studied. Using the X-ray diffractometry with 2 ms time resolution the dynamics of the 004 and 008 diffraction peak parameters (the angular position and the integral intensity) variation was determined. Two types of processes caused by the redistribution of the charge localized at the surface of the polar dielectric and by the migration of lithium ions have been observed with different velocity and response time to the external field switching. The measurements are carried out at voltages at which the induced effects have reversible characters. The use of two orders of diffraction with different X-ray extinction lengths made it possible to visualize space charge layers near the anode and cathode by the intensity variation of the diffraction peaks. The estimation of the effective thickness of the charged near-surface layer gives the value of 25 $\mu$m for lithium ions at the cathode and about 45 $\mu$m for lithium vacancies at the anode.