Formation Energy of Superlattice for Ni₃Fe, I Co-Operative Formation of Superlattice at the Critical Temperature

Abstract

Variation of inner energy for Ni₃Fe with time of the annealing at critical ordering temperature 490°C are observed first by measuring the excess specific heat of the specimen annealed with various duration, and secondly by measuring the rate of decrease of inner energy at 490°C using a new experimental method in which the necessary difference of temperature between the specimen and the surrounding wall for keeping the specimen at constant temperature 490°C is measured. Then, the variation of inner energy shows a tendency of two steps character which had been observed until now for many other physical quantities of this alloy. Next, this phenomenon has been analysed as a simple superposition of two kinds of formation processes, i.e., a formation of short range order, which starts abruptly from the beginning and ends at about 15 hours of annealing, and a formation of long range order, which begins with a sufficiently small rate, increases gradually to its maximum at 20∼30 hours and then decreases to zero at about 60 hours of annealing.