Thermodynamic origin of the structural transition pathway in metal oxide nanoparticles under acoustic shocked conditions

The nature of phase transition pathways in solids under acoustic shock conditions is largely unknown. Herein, we critically examine the structural transition of 17 metal oxide nanoparticles, which include AX-, AX₂-, A₂X₃- and A₃X₄-type oxides under similar shocked conditions. Post shock, while most of the oxides exhibit stable crystal structures, some demonstrate temperature-driven pathways and few exhibit pressure-driven transitions. In particular, two key factors, namely, thermal conductivity-dependent molten pool nucleation gap and cation chemoselectivity, are found to determine the transition type. The proposed interpretation may bring about new structural transition concepts under extreme conditions.