Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2012-02-20
Physics
Condensed Matter
Strongly Correlated Electrons
13 pages, 11 figures, 1 table, with small corrections of v1, accepted in Phys. Rev. B
Scientific paper
We report a systematic study of the $c$ lattice parameter in the Na$_{x}$CoO$_{2}$ phases versus Na content $x>0.5$, in which sodium always displays ordered arrangements. This allows us to single out the first phase which exhibits an AF magnetic order at a N\'eel temperature $T_{N}=$22 K which is found to occur for $x\approx 0.77(1)$. Pure samples of this phase have been studied both as aligned powders and single crystals. They exhibit identical $^{23}$Na NMR spectra in which three sets of Na sites could be fully resolved, and are found to display $T$ dependencies of their NMR shifts which scale with each other. This allows us to establish that the $T$ variation of the shifts is due to the paramagnetism of the Co sites with formal charge state larger than 3$^{+}$. The existence of a sodium site with axial charge symmetry and the intensity ratio between the sets of $^{23}$Na lines permits us to reveal that the 2D structure of the Na order corresponds to 10 Na sites on top of a 13 Co sites unit cell, that is with $x=10/13\approx 0.77$. This structure fits with that determined from local density calculations and involves triangles of 3 Na sites located on top of Co sites (so called Na1 sites). The associated ordering of the Na vacancies is quite distinct from that found for $x<0.75$.
Alloul Henri
Ciomaga V.-C.
Collin Gaston
Dmitriev Ya. V.
Dooglav A. V.
No associations
LandOfFree
23Na NMR study of sodium order in NaxCoO2 with 22K Neel temperature does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with 23Na NMR study of sodium order in NaxCoO2 with 22K Neel temperature, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and 23Na NMR study of sodium order in NaxCoO2 with 22K Neel temperature will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-564368