Hrem imaging and simulation with image processing for the study of phase transformations in nanometric zirconia powders

Abstract

Submicronic or nanometric particles now used as powder materials for the sintering of oxide-based ceramics, like zirconia, require techniques having the appropriate resolution for characterization. Here are presented high resolution transmission electron microscopy (HREM) studies of nanometric (non-doped) ZrO₂ powders processed by low-temperature routes for industrial use. It is shown that careful HREM imaging of such powders allows one to study the morphological and structural changes accommodating the phase transformations which can occur in these powders calcined at increasing temperatures. Three-dimensional reconstruction of the shape of the particles has been achieved by comparison of experimental HREM micrographs with simulated images. Internal strains have been revealed in the same way. Finally, image processing which allows one to separate the contributions of the different beams to the HREM image, can reveal structural defects hidden in the initial image.