Revisiting Thermodynamic Arguments and Cystallization Pathways to Understand the Phase Stability of Oxide Nanocrystals

Colloidal nanocrystals of functional materials have been a significant focus on materials chemistry and synthesis for academic and industrial scientists and engineers over the past few decades. By studying nanocrystal synthesis through a colloidal approach, we can gain new insights into the nucleation and growth process and its phase stability. In this context, we use a case study focused on synthesizing Zirconium oxide (ZrO₂) nanocrystals to demonstrate how a thermodynamic surface energy analysis can elucidate the phase stability at the nanoscale. ZrO₂ is an excellent model material for this investigation due to the well-documented crystallization process involving amorphism and polymorphism in the existing literature. We illustrate that the crossover points and regions of phase stability can be influenced by altering the surface energy of the phases. <div>Moreover, we offer a plausible explanation for the correlation between the reaction pathway and the variation in surface energy by examining the ability of organic ligands to coat the surface of the formed nanocrystal. Additionally, we introduce a new criterion for phase formation based on chemoselectivity. We suggest that chemoselectivity could be determined by factors such as the acid dissociation constant (pKa) of the ligand and other molecules present in the reaction medium, the ligand's conformational entropy, and the degree of ligand-ligand packing on the nucleus surface.</div>