Constitution of the Magnesium-Indium System near the Composition of Mg_3In and Phase Transition of β_1 Phase (Physics)

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\u27 phase is prevented by the two phase region in the whole composition range investigated. In addition to this, location of Mg_5In_2 phase (β_3 phase) in the diagram was for the first time made clear. β_3 phase is stable only below 210℃ and decomposes into β\u27 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