Electrical-transport characteristics of as-grown and oxygen-reduced La$_{0.7}$Ce$_{0.3}$MnO$_3$ films: calculation of hopping energies, Mn valences, and carrier localization lengths

TL;DR

This study investigates the electrical transport mechanisms in La$_{0.7}$Ce$_{0.3}$MnO$_3$ thin films, analyzing how oxygen deficiency and CeO$_2$ clusters influence hopping conduction, and calculates key parameters like hopping energies and Mn valences.

Contribution

It provides a comparative analysis of how oxygen deficiency and CeO$_2$ clustering affect hopping conduction mechanisms in La$_{0.7}$Ce$_{0.3}$MnO$_3$ films, including calculation of relevant transport parameters.

Findings

Oxygen deficiency and CeO$_2$ clusters significantly alter hopping mechanisms.

Film thickness has minimal impact on electrical transport.

Different hopping models fit the resistance-temperature data effectively.

Abstract

Presently, cerium-doped LaMnO$_3$ is vividly discussed as an electron-doped counterpart prototype to the well-established hole-doped mixed-valence manganites. Here, La$_{0.7}$Ce$_{0.3}$MnO$_3$ thin films of different thicknesses, degrees of CeO$_2$ phase segregation, and oxygen deficiency, grown on SrTiO$_3$ single crystal substrates, are compared with respect to their resistance-vs.-temperature (R vs. T) behavior from 300~K down to 90~K. While the variation of the film thickness (and thus the degree of epitaxial strain) in the range between 10~nm and 100~nm has only a weak impact on the electrical transport, the degree of oxygen deficiency as well as the existence of CeO$_2$ clusters can completely change the type of hopping mechanism. This is shown by fitting the respective \textit{R-T} curves with three different transport models (adiabatic polaron hopping, Mott variable-range hopping, Efros-Shklovskii variable-range hopping), which are commonly used for the mixed-valence manganites. Several characteristic transport parameters, such as the hopping energies, the carrier localization lengths, as well as the Mn valences are derived from the fitting procedures.