Phase diagram of Nax CoO2 (x0.71) 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 0.76x0.82 and 0.83x0.86. 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 ∼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 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.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|State||Published - 6 Aug 2009|