Electronic State of the ~(57)Fe Probe Atoms in Perovskites LaMO_3 (M = Ni, Cu)

摘要

Mossbauer spectroscopy has been applied for comparative study of the electronic state of probe iron atoms in perovskite-like nikelate LaNi_(0.99)~(57)Fe_(0.01)O_3 and cuprate LaCu_(0.99)~(57)Fe_(0.01)]O_3. The valence states of the ~(57)Fe atoms in these isostructural matrices are significantly different. In the nikelate, the iron atoms are in one of its ordinary valence state Fe~(3+), whereas, in the cuprate, the iron atoms have the formal oxidation state +4, as follows from hyperfine coupling parameters. The observed differences between the valence states of the ~57Fe probe atoms are attributed to the different electronic structures of the Ni and Cu atoms in the perovskites. Configuration interaction calculations show that the major contribution to the electronic state of the cation-anion complex [NiO_6]~(9-) in the nikelate is made by the d~7 configuration. For the cuprate, the d~9L configuration dominates the electronic state of the [CuO_6]~(9-) complex. The existence of one electron hole (L) on oxygen atoms leads to partial charge transfer from the doped iron atoms in the cuprate, Fe~(3+)(d~5) + O~-(L) - > Fe~(4+)(d~4) + O~(2-). As a result, the ground state of the dopant cation-anion complex FeO_6 can be represented as a superposition of configurations, d~4 (55 percent) and d~5L (45 percent).