Strain-driven structural selection and amorphization during first-order phase transitions in nanocrystalline Ho2O3 under pressure

Pressure-induced first-order phase transition often involves spatial disruption around the nucleus of a new phase, due to the inherent volume change. Atomic relaxations during this process produce lattice strain that in turn affects the nucleation kinetics and dynamics of transition, especially in nanoparticles. However, it is difficult to experimentally measure the lattice strain of materials, leading to many unsettled questions regarding size-dependent phenomena in nanomaterials at pressure. Here we present a method to determine the lattice strain of nanoparticles during first-order phase transitions using the pressure-volume data. A case study of nano-${\mathrm{Ho}}₂{\mathrm{O}}₃$ with multiple pressure-induced phase transitions is systematically performed to reveal the critical role of lattice strain in the size-dependent phase selection and amorphization. A phenomenological model is also given to describe the metastability of intermediate phases and size-tunable phase evolution during the nucleation of new phases at pressure.