Pressure-induced phase transformation in controlled shape ZnO nanorods

We present an in situ energy-dispersive X-ray diffraction study of pressure-induced phase transformations in ZnO nanorods and the corresponding bulk material up to 35.0 GPa at room temperature. ZnO nanorods with the wurtzite (P63mc) structure start to transform to a rocksalt (Fm3m) structure at a pressure of 8.0 GPa, a pressure appreciably higher than the value observed for the bulk material (7.0 GPa). This behavior suggests that both the volume collapse and the surface energy difference between the phases involved mainly govern the change of the transition pressure. The reduction of the particle size for ZnO crystallites leads to a significant increase of the bulk modulus (B0) and the pressure range of the coexistence of the wurtzite and rocksalt phases suggest that hardness of ZnO nanorods is higher than ZnO bulk.