Correlation of high temperature x-ray photoemission valence band spectra and conductivity in strained LaSrFeNi oxide on SrTiO3(110)

Reversible and irreversible discontinuities at around 573 and 823 K in the electric conductivity of a strained 175 nm thin film of (La0.8Sr0.2)(0.95)Ni0.2Fe0.8O3-delta grown by pulsed laser deposition on SrTiO3 (110) are reflected by valence band changes as monitored in photoemission and oxygen K-edge x-ray absorption spectra (XAS). The irreversible jump at 823 K is attributed to depletion of doped electron holes concomitant with reduction of Fe3+ toward Fe2+, as evidenced by oxygen and iron core level soft XAS, and possibly of a chemical origin, whereas the reversible jump at 573 K possibly originates from structural changes.