Crystal growth by ordered coalescence of lattice arrays in ZrO2-based nanocomposites at the early stage of crystallization

Abstract

Amorphous ZrO2-based nanocomposite powder synthesized by sol-gel method is often used as the raw material for preparing advanced ZrO2-based ceramics. The crystal growth process of the amorphous ZrO2-based nanocomposite powder during heat treatment has a crucial influence on the final microstructure and thus the achieved performance of ZrO2-based ceramics. However, the crystal growth process of ZrO2 nanocrystals (NCs), especially at the early stage, was ambiguous due to the lack of detailed investigation. To illustrate this issue, ZrO2-based nanocomposite powder was prepared by sol-gel method, followed by annealing at elevated temperatures. Transmission electron microscopy (TEM) was used to observe the growth process of ZrO2 NCs. Results showed that tiny ZrO2 lattice arrays without definite morphology were formed after the completion of nucleation. Nucleation might follow the classic nucleation mechanism of epitaxial growth by utilizing atoms as building blocks. Then, the randomly-oriented ZrO2 lattice arrays adopt an ordered coalescence mechanism to grow to large ZrO2 NCs. ZrO2 lattice arrays acted as building blocks and they grew rapidly by unifying their crystallography orientations. Self-perfecting, including elimination of dislocations and adjustment of lattice spacing, occurred during the growth process. Ordered coalescence of ZrO2 lattice arrays contributed to the rapid growth of ZrO2 NCs. This study deepens our fundamental understanding of the growth mechanism of amorphous ZrO2-based nanocomposite powder during heat treatment and may offer guidelines for tailoring the final microstructure and performance of ZrO2-based ceramics.