Size-dependent phase transitions and phase reversal at the nanoscale
This article investigates size-dependent phase transitions and phase reversal at the nanoscale. In general, the crystallization of a nanomaterial into a particular structure is kinetically driven. However, the choice of which structure occurs in a specific size range is often a result of thermodynamics. These size-dependent phase relationships may be explored by analyzing the free energy and enthalpy of formation. This article considers the size-dependent phase stability of nanomaterials based on experimental and theoretical studies of zirconia and titania. It describes the use of bulk phase diagrams to capture important information on the stability of materials. It also highlights some of the physical parameters that influence phase transitions and phase reversal at the nanoscale, including temperature, pressure, shape, solution chemistry, surface chemistry and surface charge.