Origin of the leakage current in Zr-substituted magneto-dielectric BaFeO3−δ single-crystal films on (0 0 1) SrTiO3 substrates

Epitaxially-grown BFZO thin films with various amounts of Zr content were successfully fabricated on (0 0 1) Nb doped-SrTiO3 substrates using the pulsed laser-beam deposition technique. The Zr substitution caused a substantial decrease in the leakage current density of the films. According to the analysis of the origin of the leakage current behaviour, the samples with x values smaller than 0.7 were found to show Poole–Frenkel (PF) type leakage properties at high electric fields, and the samples with larger x values exhibited Schottky-type behaviour. Regarding the x = 0.7 sample, it was considered that the currents of the PF- and Schottky-type behaviours determined the leakage properties of the samples, resulting in an intermediate state. The observed mechanism change is discussed in conjunction with the electronic band structure change, which may be caused by the increase in the relative amount of Zr ions, as well as by the change in the valence state of the Fe ions associated with Zr substitution.