Nanoscale and macroscopic electrical ac transport along conductive domain walls in lithium niobate single crystals

Abstract

The electrical impedance properties of UV-illuminated (λ = 310 nm) charged, conductive domain walls (CDWs) in 5 mol% magnesium-doped lithium niobate (LNO) single crystals are investigated on the nm-length scale using nanoimpedance microscopy (NIM) as well as by comparing the macroscopically measured complex impedance response between multi- and single-domain LNO samples. Similar to the case of dc conductivity, a higher conductivity of domain walls (DWs) compared to the bulk insulating matrix was observed. The contrast between DWs and bulk is most pronounced at lower frequencies (f 200 Hz) due to the large bulk capacitance at higher frequencies. Moreover, the simultaneous application of both an ac and dc bias results in an increased real part of the ac DW current. Also, equivalent circuits accurately describing both the domain and CDW contributions were developed; as a result we are able to analyze and quantify the complex dielectric conductive behavior of both bulk and CDWs in LNO within the framework of the mixed conduction model. Hopping of excited charge carriers along the CDWs was identified as the dominant charge transport process.