Sodium ordering in NaxW18O49

Sodium insertion in W18O49 proceeds through the formation of a solid soluti on for the whole range of intercalant NaxW18O49 with 0 less than or equal t o x less than or equal to 1.8. The different features detected in -partial derivative x/partial derivative E vs E plots have been associated with cont inuous phase transitions. In order to know more about these transitions, se veral samples NaxW18O49 with compositions around the minimum in the -partia l derivative x/partial derivative E curve have been synthesized and then ch aracterized by both X-ray and electron diffraction techniques, An interesti ng correlation with the electrochemical results has been established. (C) 2 000 Academic Press.