Small-Angle Neutron Scattering Study of Metallic Sodium on Phase Transition

In metallic sodium, a characteristic waiting time, which is the incubation time until phase transition starts, appears above M_s at a fixed temperature. Small-angle neutron scattering from clusters of the low-temperature phase is observed, which shows good agreement with the aggregation-of-spheres model, whose radius distribution is a Maxwell distribution function. Using the aggregation-of-spheres model, the average radius, r₀, of clusters of the low-temperature phase was found to be 57.2 Å. Moreover, abnormal small-angle neutron scattering from local fluctuations is seen during the waiting time, where this waiting time is related to the nucleation process in the martensitic phase transition.