Publication Details

de Vaulx, C., Julien, M., Berthier, C., Horvatic, M., Bordet, P., Simonet, V., Chen, D. P. & Lin, C. T. (2005). Nonmagnetic insulator state in Na1CoO2 and phase separation of Na vacancies. Physical Review Letters, 95 (18), 186405-1-186405-4.


Crystallographic, magnetic, and NMR properties of a NaxCoO2 single crystal with x≃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≃0.8 and the occurrence of a metal-insulator transition for x→1.



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