High Temperature X-ray Diffraction Study of Reaction Rates in Ceramics

The reaction rates and formation mechanisms of various n=3 Aurivillius phases were studied. Current research has shown that in order to make phase pure materials via solid-state synthesis, over 100 hours of heat treatment are necessary. A custom high temperature X-ray diffractometer (HTXRD) was utilized to observe in-situ formation reactions. The Bi2Sr2Nb2TiO12 formation reaction could not be followed to completion in-situ, but the initial reactions were clarified. Starting with precursor powders, at least two Aurivillius phases formed by 650°C, and at 1250°C there was a mixture of SrTiO3, Bi2O3, SrBi2Nb2O9, Bi2Sr2Nb2TiO12, and SrBi4Ti4O15. A phase purity study was done of Aurivillius phases containing aluminum and gallium (Bi2Sr2Nb2GaO11.5 and Bi2Sr2Nb2AlO11.5). Phase purity is in question for PDF cards 50-0498 and 50-0499, identifying Bi2Sr2Nb2AlO11.5 and Bi2Sr2Ta2AlO11.5. Three distinct phases were found present in polished samples investigated using back-scattered electron imaging and analytical transmission electron microscopy.