Charge Self-Regulation Upon Changing the Oxidation State of Transition Metals in Insulators

Hannes Raebiger, Stephan Lany, Alex Zunger

Research output: Contribution to journalArticlepeer-review

230 Scopus Citations

Abstract

Transition-metal atoms embedded in an ionic or semiconducting crystal can exist in various oxidation states that have distinct signatures in X-ray photoemission spectroscopy and 'ionic radii' which vary with the oxidation state of the atom. These oxidation states are often tacitly associated with a physical ionization of the transition-metal atoms - that is, a literal transfer of charge to or from the atoms. Physical models have been founded on this charge-transfer paradigm, but first-principles quantum mechanical calculations show only negligible changes in the local transition-metal charge as the oxidation state is altered. Here we explain this peculiar tendency of transition-metal atoms to maintain a constant local charge under external perturbations in terms of an inherent, homeostasis-like negative feedback. We show that signatures of oxidation states and multivalence - such as X-ray photoemission core-level shifts, ionic radii and variations in local magnetization - that have often been interpreted as literal charge transfer are instead a consequence of the negative-feedback charge regulation.

Original languageAmerican English
Pages (from-to)763-766
Number of pages4
JournalNature
Volume453
Issue number7196
DOIs
StatePublished - 2008

NREL Publication Number

  • NREL/JA-2A0-43072

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