Nonmagnetic insulator state in Na1CoO2 and phase separation of na vacancies.
Crystallographic, magnetic, and NMR properties of a Na1CoO2 single crystal with x approximately = 1 are presented. We identify the stoichiometric Na1CoO2 phase, which is shown to be a nonmagnetic insulator, as expected for homogeneous planes of Co3+ ions with S = 0. In addition, we present evidence that, because of slight average Na deficiency, chemical and electronic phase separation leads to a segregation of Na vacancies into the well-defined, magnetic, Na0.8CoO2 phase. The importance of phase separation is discussed in the context of magnetic order for x approximately = 0.8 and the occurrence of a metal-insulator transition for x --> 1.
de Vaulx
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Laboratoire de Spectrométrie Physique, Université J. Fourier & UMR5588 CNRS, Saint Martin d'Hères, France.
Julien
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Berthier
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Horvatić
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Bordet
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Simonet
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Chen
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DP
Lin
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