DIFFaX SIMULATIONS OF POLYTYPISM AND DISORDER IN HYDROTALCITE

摘要

DIFFaX simulations show that the 3R_1 and 3R_2 polytypes of hydrotalcites (HT) have distinctly different X-ray powder diffraction (XRPD) patterns. The HT samples obtained by copredpitation as well as those subjected to a subsequent hydrothermal treatment exhibit non-uniform broadening of lines in their XRPD patterns as well as anomalous variation in the intensities of the basal reflections. The reflections appearing in the mid-2θ region (30-50°; 3- 1.8 A) are excessively broadened and do not correspond to either of the 3R polytypes. This broadening is shown to be due to a stacking of layers randomly rotated about the c crystallographic axis by n x 120° (n = 1,2). The intensities of the basal reflections vary due to the departure of the layer composition from the nominal value, essentially due to an increase in the intercalated water content.