Direct determination of thermal expansion coefficients from the profile fitting of a diffractogram

Abstract This paper presents a set of files for working with Topas software in order to calculate the thermal expansion coefficients of a crystal phase as a function of the temperature from a set of powder diffractograms. All the calculations and profile fittings are performed in the same run, in cascade and without interruption. Free graphics software GNUPLOT reads the output files in order to display both the characteristic three-dimensional thermal expansion surface and any section of this surface. The results are also generated as text files. The files also calculate the thermal expansion coefficients in any [u, v, w] direction and at any temperature, and the angles between the principal axes and the crystallographic axes. The user can modify the input text files to their requirements. The calculations have been checked with calculated diffractograms at different temperatures for a triclinic, monoclinic and tetragonal phase. The calculated coefficients have been compared with previous works and show good agreement. The extent to which the peak/noise ratio of the diffractogram affects the calculated thermal expansion coefficients is also discussed.