Valence changes associated with the metal-insulator transition in Bi 1 − x La x Ni O 3 </mml:…
2005; American Physical Society; Volume: 72; Issue: 15 Linguagem: Inglês
10.1103/physrevb.72.155103
ISSN1550-235X
AutoresHiroki Wadati, M. Takizawa, T. T. Tran, Kiyohisa Tanaka, T. Mizokawa, A. Fujimori, Akira Chikamatsu, Hiroshi Kumigashira, M. Oshima, Shintaro Ishiwata, Masaki Azuma, M. Takano,
Tópico(s)Multiferroics and related materials
ResumoPerovskite-type BiNiO$_3$ is an insulating antiferromagnet in which a charge disproportionation occurs at the Bi site. La substitution for Bi suppresses the charge disproportionation and makes the system metallic. We have measured the photoemission and x-ray absorption (XAS) spectra of Bi$_{1-x}$La$_{x}$NiO$_{3}$ to investigate how the electronic structure changes with La doping. From Ni $2p$ XAS, we observed an increase of the valence of Ni from 2+ toward 3+. Combined with the core-level photoemission study, it was found that the average valence of Bi remains $\sim 4+$ and that the Ni valence behaves as $\sim (2+x)+$, that is, La substitution results in hole doping at the Ni sites. In the valence-band photoemission spectra, we observed a Fermi cutoff for $x>0$, consistent with the metallic behavior of the La-doped compounds. The Ni $2p$ XAS, Ni $2p$ core-level photoemission, and valence-band photoemission spectra were analyzed by configuration-interaction cluster-model calculation, and the spectral line shapes were found to be consistent with the gradual Ni$^{2+} \to$ Ni$^{3+}$ valence change.
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