The thermal expansion and phase transitions of WO 3

Abstract

The thermal expansion of we a from room temperature to 700 ° C. has been measured by X-ray diffraction methods. The expansion of the a and c axes of the unit cell can be represented by a smooth curve for the entire range investigated. The b axis expands uniformly from room temperature to about 300 ° C. and decreases slightly in length from 330 to 700 ° C. The monoclinic unit cell undergoes a transformation near 330 ° C. to an orthogonal form, which is probably orthorhombic. Foiix (1945) measured the thermal expansion of WOa dilatometrically and reported an average coefficient of linear expansion of about 13× 10-6 from room temperature up to about 330 ° C.; the coefficient decreased to 10 × 10-6 for the range from 330 ° to 710 ° C.