Electronic Structure of Spinel-Type MgTi2O4: Valence Change at Surface and Effect of Fe Substitution for Mg

Tomoyuki Yamaguchi, Mario Okawa, Hiroki Wadati, Tom Z. Regier, Tom Saitoh, Yasumasa Takagi, Akira Yasui, Masahiko Isobe, Yutaka Ueda, Takashi Mizokawa

Research output: Contribution to journalArticlepeer-review

Abstract

Bulk and surface electronic states of MgTi2O4 have been investigated by means of x-ray absorption spectroscopy (XAS), hard x-ray photoemission spectroscopy (HAXPES), and theoretical calculations. The Ti 2p XAS spectra exhibit multiplet structures derived from the bulk Ti3+ and surface Ti4+ features. In the surface sensitive O 1s XAS of the total electron yield mode, the magnitude of ligand field splitting is enhanced due to existence of surface Ti4+ species. The bulk-sensitive O 1s XAS spectrum taken in the total fluorescence yield mode is well reproduced by unoccupied part of O 2p density of states obtained by band structure calculations with on-site Coulomb interaction U for Ti 3d. In addition, occupied part of the calculated Ti 3d density of states agrees with the hard x-ray photoemission spectrum indicating Mottness of Ti 3d electrons. In Mg1−xFexTi2O4, the bulk sensitive Fe 2p XAS is consistent with high spin Fe2+ indicating isovalent substitution for Mg while the surface sensitive Fe 2p XAS includes high spin Fe3+. The multiplet structures in the Ti 2p and Fe 2p XAS spectra show that the 3d electrons in the bulk Ti3+ and Fe2+ are basically localized. On the other hand, a low energy shoulder of the Ti 2p HAXPES peak, which can be assigned to Ti2+ or screening effect, suggests charge fluctuation due to proximity to the metal–insulator transition.

Original languageEnglish
Article number074704
Journaljournal of the physical society of japan
Volume91
Issue number7
DOIs
Publication statusPublished - 2022 Jul 15

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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