Competition between surficial and volumetric diffusion in sintering TiO2 polymorphs by molecular dynamics simulation

The competition between surficial and volumetric diffusion during the sintering process for ceramic polymorphism at different sintering temperatures is worth deeply exploring. In the current work, various sintering cases of mixed TiO₂ nanoparticles with rutile and anatase types were investigated and the effects of crystalline phase, sintering temperature, and particle size on the sintering process were systematically investigated. The difference in thermodynamic stability and surficial activity of the crystalline phase could promote the decomposition and densification of the nanoparticles. Comparing the mixed-phase sintering process at different sintering temperatures, the results showed that the particle binding process at low temperature relied mainly on surficial diffusion, however, volumetric diffusion played a crucial role at high temperature. The internal occurrence of volumetric diffusion inhibited the surficial diffusion, resulting in a smaller diameter of the sintering neck and a different sintering rate. In the case of sintering three nanoparticles with rutile and anatase types, it could be found that the decomposition of nanoparticles is more uniform in mixed-phase sintering at high temperatures and the sintering rate is not significantly influenced by the sintering temperature. This work demonstrates the advantage of a mixed-phase sintering strategy for TiO₂ nanoparticles, which could provide insight into ceramic materials with polymorphism.