Emergent charge ordering in near half doped Na0.46CoO2

We have utilized neutron powder diffraction to probe the crystal structure of layered NaxCoO2 near the half doping composition of x 0.46 over the temperature range of 2 600 K. Our measurements show evidence of a dynamic transition in the motion of Na ions at 300 K, which coincides with the onset of a near zero thermal expansion in the in plane lattice constants. The effect of Na ordering on the CoO2 layer is reflected in the octahedral distortion of the two crystallographically inequivalent Co sites and is evident even at high temperatures. We find evidence of a weak charge separation into stripes of Co 3.5 and Co 3.5 amp; 8722; , 0.06e below TCO 150 K. We argue that changes in the Na 1 O bond lengths observed at the magnetic transition at Tm1 88 K reflect changes in the electronic state of the CoO2 laye