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arXiv · 0901.0622

Staging model of the ordered stacking of vacancy layers and phase separation in the layered NaCoO(x > 0.71) single crystals

G. J. Shu·F. -T. Huang·M. -W. Chu·J. -Y. Lin·Patrick A. Lee·F. C. Chou
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Abstract

Phase diagram of Na$_x$CoO$_2$ (x $\gtrsim$ 0.71) has been reinvestigated using electrochemically fine tuned single crystals. Both phase separation and staging phenomena as a result of sodium multi-vacancy cluster ordering have been found. Phase separation phenomenon is observed in the narrow ranges of 0.76 $\lesssim$ x $\lesssim$ 0.82 and 0.83 $\lesssim$ x $\lesssim$ 0.86. While x = 0.820 shows A-type antiferromagnetic (A-AF) ordering below 22K, x = 0.833 is confirmed to have a magnetic ground state of A-AF ordering below $\sim$8K and is only reachable through slow cooling. In addition, x = 0.859 is found to be responsible for the highest A-AF transition temperature at about 29K. Staging model based on ordered stacking of multi-vacancy layers is proposed to explain the hysteretic behavior and A-AF correlation length for x $\sim$ 0.82-0.86.

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G. J. Shu, F. -T. Huang, M. -W. Chu, J. -Y. Lin, Patrick A. Lee, F. C. Chou. 2009-07-13. Staging model of the ordered stacking of vacancy layers and phase separation in the layered NaCoO(x > 0.71) single crystals. https://arxiv.org/abs/0901.0622

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