Electronic structure of the negative charge-transfer material Sr 3Fe MO 7 ( M=Fe, Co, Ni)

Abstract

We studied the electronic structure of the substituted Sr 3Fe MO 7 compounds ( M=Fe, Co, Ni). The experimental technique used in the study was M 2 p X-ray photoelectron spectroscopy (XPS). The charge-transfer satellites in the M 2 p spectra were analyzed using cluster model calculations. The analysis indicates that these materials are in the negative charge-transfer regime, and that their ground states are dominated by the 3 d n+1 L configuration (where L denotes a 2 p hole in the oxygen band). The results are similar to those found in the closely related SrFeO 3 and SrCoO 3 compounds. The band gap of these compounds is split off by the relatively large value of the p– d transfer integral T σ The lowest lying excitations are 3 d n+1 L+3 d n+1 L → 3 d n+1+3 d n+1 L 2 and the band gap is of the p– p type. The value of the p– d transfer integral T σ in the Sr 3Fe MO 7 compounds decreases from Fe to Ni. In turn, this helps to explain the increase in the electrical conductivity along the M=Fe, Co, Ni series.