The process of the defect structure rearrangement in a lithium tetraborate single crystal under the influence of high voltage external electric field applied along the polar direction [001] is studied with use of X-ray diffractometry. The results are supplemented by measurements of the conductivity kinetics. Under conditions of electric field of 300-500 V/mm strength, a sharp broadening of the 004 reflection diffraction peak and its integral intensity increasing by several times are observed, however its position and shape practically do not change. Under the influence of DC field with a strength in range of 500 to 1500 V/mm, the broadening process slows down, but the rocking curve asymmetry appears as well as its sharp shift to the smaller angles associated with an increase in the lattice parameter along the c-axis. This process is quasi-reversible, since the distorted structure is partially restored at a very slow rate (for several months). Two types of the diffraction peak parameters variation dependencies on the external field are interpreted as the manifestation of two ionic conductivity mechanisms: mobile lithium ions (Li+) at low-intensity electric field and oxygen vacancies (VO2+) at stronger fields. The process of charge carriers’ migration causes the increase of defects concentration and structure changes in the near-surface region of the crystal.

Using the method of time-resolved X-ray diffractometry in a three-crystal scheme, the lattice deformation of a rubidium biphthalate (С8H5RbO4) crystal was measured in an external electric field. Under the action of an external pulsed electric field along the [001] polar direction, the piezoelectric moduli d31, d32, and d33 were determined independently using three reflections 400, 070, and 004; the obtaind values are –32.8 ± 0.6, 12.8 ± 0.3, and 21.8 ± 1.2 pC/N, respectively. A good agreement was found between the values of the piezoelectric moduli obtained in this work and the values obtained earlier by the quasi-static method.

The results of study of the defect structure variation process in the near-surface layers of lithium tetraborate (Li2B4O7) single crystals under the influence of an external electric field applied along the [001] polar direction are presented. Using the X-ray diffractometry with 2 ms time resolution the dynamics of the 004 and 008 diffraction peak parameters (angular position and integral intensity) variation was determined. Two types of processes caused by redistribution of the charge localized at the surface of the polar dielectric and the migration of lithium ions were revealed with different velocity and response time to the external field switching. The measurements were carried out at voltages providing a reversible character of induced effects. The use of two orders of diffraction with different X-ray extinction length made it possible to visualize space charge layers near the anode and cathode by the intensity variation of the diffraction peaks. Estimation of the effective thickness of the charged surface layer gives a value of 25 μm for lithium ions at the cathode and about 45 μm for lithium vacancies at the anode.

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