Staging model of the ordered stacking of vacancy layers and phase separation in layered NaxCoO2 (x≳0.71) single crystals

• Main Authors: Shu, G. J. (Author), Huang, F.-T (Author), Chu, M.-W (Author), Lin, J.-Y (Author), Lee, Patrick A. (Contributor), Chou, F. C. (Author)
• Other Authors: Massachusetts Institute of Technology. Department of Physics (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2010-01-29T20:20:06Z.
• Subjects: Article
• Online Access: Get fulltext

Phase diagram of Na[subscript x]CoO[subscript 2](x≳0.71) has been reinvestigated using electrochemically fine-tuned single crystals. Both phase-separation and staging phenomena as a result of sodium multivacancy cluster ordering have been found. Phase-separation phenomenon is observed in the narrow ranges of 0.76≲x≲0.82 and 0.83≲x≲0.86. While x=0.820 shows A-type antiferromagnetic (A-AF) ordering below 22 K, x=0.833 is confirmed to have a magnetic ground state of A-AF ordering below ∼8 K 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 29 K. Staging model based on ordered stacking of multivacancy layers is proposed to explain the hysteretic behavior and A-AF correlation length for x ∼0.82-0.86.
Department of Energy
National Science Council of Taiwan