DIFFAX SIMULATIONS OF POLYTYPISM AND DISORDER IN HYDROTALCITE

Abstract

DIFFaX simulations show that the 3R1 and 3R2 polytypes of hydrotalcites (HT) have distinctly different X-ray powder diffraction (XRPD) patterns. The HT samples obtained by coprecipitation 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-2 region (30 - 50°; 3 - 1.8 Å) are excessively broadened and do notcorrespond 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 × 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.