Amorphization in Nanoparticles

Nanoparticles have more propensities for amorphization than their bulk counterparts, opening the opportunity to achieve the amorphous states in well-known poor glass-former compounds. Classical size effects are often invoked to explain such phenomenon. However, this argument is not sufficient to cover all experimental results such as functionalization effect. In this work, Y2O3 nanoparticles of 7 nm diameter are investigated under pressure. Special care is taken on the surface state of the particles by comparing the pressure-induced transformation of nanoparticles stored under different conditions (atmospheric vs argon environment). A clear difference is reported as one batch shows a transformation to an amorphous state, whereas the second undergoes a crystal-to-crystal transition. These results are discussed in terms of interface energy taking into account not only the usual surface energy but also the surface state contribution. The link between different types of amorphization (pressure-, mechanical-, and radiation-induced amorphization) in nanoparticles is underlined as a critical defect density is required to achieve the crystal-to-amorphous transformation. Defect creation may arise from multiple sources: irradiation, functionalization, and reconstructive transition.