In situ TEM sintering of nano-sized ZrO2 particles

The sintering behavior of faceted, nano-sized single-crystal particles of ZrO2 has been investigated using in situ transmission electron microscope heating techniques. These direct observations have provided new information on the morphological and structural evolution of particles, necks and pores during the sintering process. The results indicate that ZrO2 particle-pairs, which are not attached to other particles and not highly constrained by the TEM grid, reorient themselves with respect to each other during sintering at 890 degrees C. This reorientation can be explained in terms of a minimization of the grain-boundary energy between the two coalescing particles. In addition to changes in particle orientation, these experiments show that the topologies of ZrO2 particles and their associated necks evolve during heating. During the in situ TEM heating of these particles, the dynamic motion of atom clusters (10-100 atoms) on and off of surfaces is observed, as is the formation and dissolution of ledges and steps on previously smooth facets. The phenomenon of cluster migration is discussed and the ramifications of the results of this study for more highly constrained systems of particles (e.g. ceramic green-bodies) are also considered.