The comprehensive description of both the electrical transport along conductive domain walls in lithium niobate single crystals and the charge injection at the interfacing metal electrodes, emerged to be a complex challenge. Recently, a heuristic evaluation allowed to postulate the “$R2D2$” equivalent-circuit model (consisting of two parallel resistor-diode pairs) to appropriately match the dc current-voltage (I-V) characteristics. Here, we carefully revisit the interfacial electrical behavior, i.e., the diode part of the equivalent circuit model, since many more processes beyond the diode-related electron hopping transport (HT) assumed so far, may concurrently occur, such as thermionic emission (TE), Fowler-Nordheim tunneling (FNT), space-charge limited conduction (SCLC), and others. The “$R2D2$” model thus needs to be generalized into an “$R2X2$” circuit model (with $X$ = HT, TE, FNT, SCLC, and others) to fit to the experimental data. Moreover, to check for the best I-V curve fitting to the different theories, we apply a higher-harmonic DW current-contribution analysis, i.e., an ac I-V inspection, that allows us to discriminate between all these possible models with much higher precision than from pure dc I-V curve fitting. Both the ac and dc analysis yield consistent results, finding that the FNT model accounts best for the domain-wall/electrode junctions investigated here.

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• Domain walls
• Electrical conductivity
• Ferroelectric domains
• High-order harmonic spectroscopy
• Resistivity measurements