Studies of MgAlPd icosahedral quasicrystals and approximant crystals synthesized by the mechanical alloying process

Abstract

MgAlPd quasicrystals prossessing the rhombic triacontahedron (RT) cluster as a structural unit were prepared by the mechanical alloying (MA) process. The MA process is an efficient method of determining the region of the RT-type icosahedral quasicrystalline phase (I-phase), because it forms directly from the crystalline elemental powder within a few hours by solid state reaction. In a previous study, the region of formation of the thermally stable I-phase and related approximant phases was determined in the MgAlZn system. In this study, we determined the region of formation of the I- and 1 1 - approximant phases in the MgAlPd system and we compare the region of formation and thermal stability of the I- and the 1 1 approximant phases in the MgAlPd system with those in the MgAlZn system. We conclude that both the Mg concentration and the average number of sp-valence electrons per atom play a critical role in determining the formation area of the thermally stable I- and 1 1 - phases in the MgAlPd and the MgAlZn systems.