LAUSR

DOI: 10.1002/aelm.201700242 devices,[10] and the fundamental inspection by theory and experiment. While ferroelectrics constitute wideband gap semiconductors with good insulating properties, their DWs may possess a significantly increased electrical conductivity, as is of central focus in the work here. This so-called domain wall conductivity (DWC) has been reported first for multiferroic bismuth ferrite[11] and lead-zirconate-titanate[12] thin films, followed by research on (improper) erbium manganite[13] and barium titanate[14] bulk ferroelectric crystals. DWC in lithium niobate (LiNbO3:LNO) so far was reported to happen under photoexcitation only.[15,16] However, recent experiments by Godau et al.[17] on LNO single crystals (sc) have shown that reshaping the DW to larger inclination angles by applying a dedicated electrical tuning protocol enhances DWC by 3–4 orders of magnitude, and gives rise to DW currents in the upper μA range at room temperature and in the dark. Theoretical approaches applied to explain the increased DWC in these materials include phenomenological Landau[18] and Landau–Ginzburg–Devonshire theory,[19] and more recently also the combination of quantum mechanics with phenomenological Landau theory.[20] All these microscopic theories aim at predicting and quantifying the relevant local-scale domain wall parameters, i.e., the DW formation energy, the free charge distribution, and the DW conductivity. Nevertheless, it is difficult to compare the outcomes of such microscopic theories directly to experimental data, as the latter generally is based on macroscopic quantities. In contrast, our resistor network (RN) approach provides a clue link to experiments, in spite of being nonpredictive (i.e., as it requires some initial experimental input). Hence, our results can be directly compared to the local currents flowing within the DW as measured for instance by conductive atomic force microscopy (cAFM). The simple picture of a RN thus elegantly complements the microscopic theories of DWC.