Sodium Ordering in NaxW18O49

Sodium insertion in W18O49 proceeds through the formation of a solid solution for the whole range of intercalant NaxW18O49 with 0≤x≤1.8. The different features detected in −∂x/∂E vs E plots have been associated with continuous phase transitions. In order to know more about these transitions, several samples NaxW18O49 with compositions around the minimum in the −∂x/∂E curve have been synthesized and then characterized by both X-ray and electron diffraction techniques. An interesting correlation with the electrochemical results has been established.