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

Abstract : The present high-pressure studies of CuFeO2 to 30 GPa using x-ray diffraction, along with F57e 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 R3¯m structure (0-18 GPa) is composed of sheets of FeS=5/23+ ions alternating with layers of O-CuS=01+-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-CuS=01+-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 (CuS=01+FeS=5/23+)→(CuS=1/22+FeS=22+) 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 P3¯m , and (ii) the Néel temperature increases above twofold [TN(CuS=1/22+FeS=22+)≈2.2TN(CuS=01+FeS=5/23+)] . This sequence of transitions is reversible with minimal hysteresis.
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https://hal-insu.archives-ouvertes.fr/insu-00553391
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Submitted on : Friday, January 7, 2011 - 12:50:40 PM
Last modification on : Friday, September 25, 2020 - 3:13:57 AM

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W. M. Xu, G. Kh. Rozenberg, M. P. Pasternak, M. Kertzer, A. Kurnosov, et al.. Pressure-induced Fe↔Cu cationic valence exchange and its structural consequences: High-pressure studies of delafossite CuFeO2. Physical Review B: Condensed Matter and Materials Physics, American Physical Society, 2010, 81, pp.104110. ⟨10.1103/PHYSREVB.81.104110⟩. ⟨insu-00553391⟩

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