Kinetics of ordering in Ni_1.50Sn (‘Ni₃Sn₂’) as revealed by the variation of the lattice parameters upon annealing

Abstract

X-ray powder diffraction was employed to reveal the structural changes occurring upon annealing of quenched, hexagonal Ni_1.50Sn below its equilibrium ordering temperature, leading finally to long-range ordered, orthorhombic Ni_1.50Sn. The changes in the diffraction patterns indicate that the features of the low-temperature phase develop gradually in two main stages. Ex situ and in situ time-resolved X-ray powder diffraction analysis of the first stage was employed to monitor at various temperatures the time dependence of the lattice axial ratio c/a associated with the formation of long-range order in small domains. Data evaluation using an ‘equivalence-time’ method gave a value of 165–170 kJ/mol for the activation energy of the ordering, indicative of lattice-site changes of Ni atoms.