An electron hole doping and soft x-ray spectroscopy study on La1-xSrxFe0.75Ni0.25O3-{\delta}

TL;DR

This study investigates the electronic structure and conductivity of La1-xSrxFe0.75Ni0.25O3-{ extdelta} using soft X-ray spectroscopy, revealing optimal doping levels and the effects of hole doping on electronic properties relevant for fuel cell cathodes.

Contribution

It provides new insights into the relationship between doping, electronic structure, and conductivity in La1-xSrxFe0.75Ni0.25O3-{ extdelta} using soft X-ray spectroscopy.

Findings

Maximum conductivity at x=0.5 (~678 S/cm)

Lowest activation energy for polaron conduction at x=0.5 (39 meV)

Linear correlation between hole doping and oxygen K-edge pre-peak variation

Abstract

The conductivity of the electron hole and polaron conductor La1-xSrxFe0.75Ni0.25O3-{\delta}, a potential cathode material for intermediate temperature solid oxide fuel cells, was studied for 0 <x < 1 and for temperatures 300 K <T < 1250 K. In LaSrFe-oxide, an ABO3 type perovskite, A-site substitu-tion of the trivalent La3+ by the divalent Sr2+ causes oxidation of Fe3+ towards Fe4+, which forms conducting electron holes. Here we have in addition a B-site substitution by Ni. The compound for x = 0.5 is identified as the one with the highest conductivity ({\sigma} ~ 678 S/cm) and lowest activation energy for polaron conductivity (Ep = 39 meV). The evolution of the electronic structure was monitored by soft x-ray Fe and oxygen K-edge spectroscopy. Homogeneous trend for the oxida-tion state of the Fe was observed. The variation of the ambient temperature conductivity and activation energy with relative Sr content (x) shows a correlation with the ratio of (eg/eg+t2g) in Fe L3 edge up to x=0.5. The hole doping process is reflected by an almost linear trend by the variation of the pre-peaks of the oxygen K-edge soft x-ray absorption spectra.