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Covalency Competition in the Quadruple Perovskite CdCu3Fe4O12

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journal contribution
posted on 19.07.2017, 19:14 authored by Ikuya Yamada, Akihiko Takamatsu, Naoaki Hayashi, Hidekazu Ikeno
Cadmium ions (Cd2+) are similar to calcium ions (Ca2+) in size, whereas the Cd2+ ions tend to form covalent bonds with the neighboring anions because of the high electronegativity. The covalent Cd–O bonds affect other metal–oxygen bonds, inducing drastic changes in crystal structures and electronic states. Herein, we demonstrate high-pressure synthesis, crystal structure, and properties of a new quadruple perovskite CdCu3Fe4O12. This compound exhibits an electronic phase transition accompanying a charge disproportionation of Fe ions without charge ordering below ∼200 K, unlike charge-disproportionation transition with rock-salt-type charge ordering for CaCu3Fe4O12. First-principle calculations and Mössbauer spectroscopy display that covalent Cd–O bonds effectively suppress the Fe–O bond covalency, resulting in an electronic state different from that of CaCu3Fe4O12. This finding proposes covalency competition among constituent metal ions dominating electronic states of complex metal oxides.