The thermal expansion of cubic sodium tungsten bronzes

The coefficients of thermal expansion of powdered cubic sodium tungsten bronzes (NaxWO3; 0.9 > x > 0.3) from room tempera ture to 600 ° C. have been determined. The expansion coefficients for all compositions studied are constant and essentially identical below transi t ion temperatures (near 200 ° C.) which vary wi th sodium content . At the t rans i t ion temperatures , the expansion coefficients change sharply to lower values which vary with composition, going through a min imum near x = 0.5. The relation between these changes and a similar change in pure WO 3 is pointed out.