BLANGERO, Maxime; CARLIER-LARREGARAY, Dany; POLLET, Michaël; DARRIET, Jacques; DELMAS, Claude; DOUMERC, Jean-Pierre

doi:10.1103/PhysRevB.77.184116

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BLANGERO, Maxime
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

CARLIER-LARREGARAY, Dany
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

POLLET, Michaël
Institut de Chimie de la Matière Condensée de Bordeaux [ICMCB]

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Physical Review B: Condensed Matter and Materials Physics (1998-2015). 2008, vol. 77, n° 18, p. 184116 (8 p.)

American Physical Society

Résumé en anglais

The high temperature phase transition in the three-layered P[prime]3-NaxCoO2 (x~0.62) has been investigated by means of heat capacity measurement, x-ray diffraction, and 23Na magic angle spinning (MAS)–NMR spectroscopy in the 300–550 K range. The phase transition occurs nearby TS=350 K. Below TS, the unit cell is monoclinic (space group C2/m). Above TS, the monoclinic cell is reversibly converted into a rhombohedral cell (space group R3m). The crystallographic change mainly manifests into Na rearrangement in the interslab from a low symmetry position to a higher symmetry position. A global picture for both systems of the (x,y,z) off-center position of Na could be understood as a balance between on-site Na+-Co3+/4+ electrostatic repulsions (z shift) and in-plane Na+-Na+ electrostatic repulsions (xy shift). We suggest that Na+ interlayer redistribution is the driving force of the phase transition. 23Na MAS-NMR spectroscopy has been used to investigate changes in the environment and in the distribution of the sodium cations occurring by raising the temperature. The gradual suppression of the second-order quadrupolar interactions and the resulting new resonance is consistent with the sodium site exchange mechanism. Changes in the resistivity at TS suggest a strong coupling between the Na+ and CoO2 layers.< Réduire

Mots clés en anglais

Phase transition

Inorganic compounds

High temperature

Sodium cobaltite

MAS–NMR spectroscopy

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High-temperature phase transition in the three-layered sodium cobaltite Pf3-NaxCoO2 (x~0.62)

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