Ni 3Ga—an investigation of ordering kinetics by residual resistometry

Abstract

Order–disorder transformations in the compound Ni 3Ga with L1 2 superstructure were investigated by residual electrical resistometry during isochronal and isothermal step-annealing treatments. Resistivity measurements after several isochronal annealing treatments at rising and falling temperatures in the range at 293–800 K showed a complex annealing behavior of Ni 3Ga. The first registration of a slight atomic mobility was identified already at 380 K, followed by the second step in atomic mobility observed between 500 and 650 K and attributed to a change in the degree of long range order (LRO) in the structure. Measurements at isothermal annealing have been performed after isothermal step treatments between 673 and 786 K also at rising and falling temperatures. The analysis of electrical resistivity curves allowed for conclusion that the order–disorder equilibrium in Ni 3Ga is reached not in a single exponential process, but as a result of two processes with distinctly different rates. The ordering activation energies of both fast and slow processes in Ni 3Ga were calculated. For the first, fast relaxation process an activation energy parameter was found equal to 1.47 eV; the second, slow process was characterized by an activation energy of 2.66 eV.