Very low thermal expansion in TaO2F

X-ray diffraction data for TaO2F from 20 to 400 K show a thermal expansion so low that we cannot be certain whether it is positive or negative. We estimate the absolute value of the thermal expansion coefficient to be less than 6 x 10(-7)/K. This then is comparable to that of amorphous SiO2, and is apparently unique behavior for a cubic material over such a large temperature range. (C) 2003 Elsevier Science (USA). All rights reserved.