Crystal-to-stripe reordering of sodium ions in NaxCoO2 (x>=0.75)
  The sodium reordering in NaxCoO2 in the vicinity of room temperature is rationalized at high x in terms of phase transitions between square and striped phases. A striking hexagon-of-hexagons diffraction pattern observed for x=0.78 can be reproduced using coexisting square and striped phases that are related by simple shear deformations. All compositions exhibit a partial melting transition to a disordered stripe phase just below room temperature, which alters the topology of the electrical conduction pathways. 
D.J.P. Morris, M. Roger, M.J. Gutmann, J.P. Goff, D.A. Tennant, D.   Prabhakaran, A.T. Boothroyd, E. Dudzik, R. Feyerherm, J...