Constitution of the magnesium-indium system near the composition of Mg 3ln and phase transition of β1 phase

Abstract

The phase diagram of the Mg-In system was re-examined, as there was some uncertainty as to the phase transition of β 1 phase in the literature. It was found that the direct transition of β 1 to β' phase is prevented by the two phase region in the whole composition range investigated. In addition to this, location of Mg 6In 2 phase ( β 3 phase) in the diagram was for the first time made clear, β 3, phase is stable only below 210°C and decomposes into β 1 and β 2 phases above this temperature. The confirmation of the crystal structure of β 1 phase was also done on single crystal electron diffraction patterns. Mg 3In changes its structure from ordered 12R to disordered f.c.c. through ordered 3R with increasing temperature. The transformation energy associated with the change in the stacking sequence (12R → 3R) and that associated with the order-disorder phase change were estimated by specific heat measurements to be ~120 cal/mole and ~340 cal/mole, respectively.