Pressure-induced Fe↔Cu cationic valence exchange and its structural consequences: High-pressure studies of delafossite CuFeO2

W. M. Xu, G. Kh Rozenberg, M. P. Pasternak, M. Kertzer, A. Kurnosov, L. S. Dubrovinsky, S. Pascarelli, M. Munoz, M. Vaccari, M. Hanfland, R. Jeanloz

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Abstract

The present high-pressure studies of CuFeO2 to 30 GPa using x-ray diffraction, along with F 57 e Mössbauer and Fe and CuK -edge x-ray absorption spectroscopy methods, reveal a sequence of intricate structural/electronic-magnetic pressure-induced transitions. The low-pressure R 3̄ m structure (0-18 GPa) is composed of sheets of Fe S=5/2 3+ ions alternating with layers of O-Cu S=0 1+ -O dumbbells, the latter oriented along the c axis. This structure is characterized by an unusual positive d (c/a) /dP. At 18 GPa a structural transition takes place to a more isotropic C2/c structure with the O-Cu S=0 1+ -O axis tilted 28° from the c axis and with negative d (c/a) /dP. This transition corroborates with the onset of long-range antiferromagnetic order. Starting at ∼23GPa, with an initial volume reduction in ∼ | ΔV/ V0 | =0.16, the Cu-Fe bands overlap and this leads to a (Cu S=0 1+ Fe S=5/2 3+) → (Cu S=1/2 2+ Fe S=2 2+) interionic valence exchange in about 1/3 of the C2/c -CuFeO2 at 27 GPa. As a result: (i) the Cu2+ -O becomes fourfold coordinated and is in a new crystallographic structure with space group P 3̄ m, and (ii) the Néel temperature increases above twofold [TN (Cu S=1/2 2+ Fe S=2 2+) 2.2 TN (Cu S=0 1+ Fe S=5/2 3+)]. This sequence of transitions is reversible with minimal hysteresis.

Original languageEnglish
Article number104110
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume81
Issue number10
DOIs
StatePublished - 17 Mar 2010

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