Characterization of conduction properties of La_1.4Sr_1.6Mn₂O₇ by complex impedance spectroscopy

The electrical transport characterization of dual-layer perovskite, La_1.4Sr_1.6Mn₂O₇(327), has been systematically studied by the complex impedance technique. The complex resistivity spectra, under a dc bias (Vdc) from 0 to 400 mV, have been analyzed by an equivalent circuit model (ECM), including a resistance (R) component and two sets of parallel R and capacitance (C) components in series. The electrical elements represent the 327 grain and 327 two different (extrinsic and intrinsic) grain boundaries (GBs) contributions, respectively. The analyzing results by the ECM demonstrate the R decreases, but C increases with rising V_dcfor extrinsic phase of 327 GBs. The behavior can be assigned to the trap-states dominated conduction. For intrinsic phase of 327 GBs, R is almost independent on the V_dc but C decreases with rising V_dc, The transport behavior can be attributed to the decrease of electric dipoles rotation by increasing V_dc. It is here noted that the R element of 327 grains is almost independent on V_dc. The results indicate that two phase GBs is a predominant effect on the electrical transport for 327 and exists different transport behavior on V_dc.