Variation of a Defect Structure of Lithium Tetraborate (Li2B4O7) in an External Electric Field

Resumo

The variation of a defect structure of a lithium tetraborate single crystal under the influence of a high-strength external electric field applied along polar direction [001] has been studied by the X-ray diffraction (XDR) method. The conductivity kinetics has been measured; it is found to agree with changes in the diffraction peak parameters. Application of the electric field with the strength of 300–500 V/mm leads to a sharp broadening of the rocking curve and the increase in the integral intensity by several times, but the curve position and shape are only slightly changed. At higher electric fields from 500 to 1500 V/mm, the process of broadening the curve slows down; however, the shape asymmetry appears and the peak shifts to smaller angles, which is due to an increase in the lattice parameter along axis c. In this case, the changes become irreversible, since the distorted structure is partially recovered with a very low rate (for several months). Two types of the dependences of the rocking curves parameters variation under an external field are interpreted as the manifestation of two mechanisms of the ionic conduction due to mobile lithium (Li⁺) ions at low fields and oxygen vacancies (\({\text{V}}_{{\text{O}}}^{{2 + }}\)) at higher fields. The charge carrier migration leads to an increase in the defect concentration and structural changes in a near-surface crystal region. The obtained results have practical importance from the point of view of the controlled change in the defect structure in the crystals with ionic conductivity.