A HEXAGONAL PHASE RELATED TO QUASI-CRYSTALLINE PHASES IN ZN-MG-RARE-EARTH SYSTEM

The Z-Zn6Mg3Sm ternary phase has been studied by electron diffraction. Y and the rare-earth elements with atomic radii just below thar of Sm in Zn6Mg3RE alloys (RE = rare earth or Y) form the icosahedral phase, while with Sm it forms the Z phase. The Z phase is hexagonal with a = 12.4 Angstrom and c = 8.8 Angstrom, and with the space group P6(3)/mm c. The relationship of this phase to the icosahedral quasicrystal is d emonstrated through diffraction features. It is shown that this hexago nal phase consists of three icosahedral units rotated by 120 degrees a bout a common twofold axis, forming the sixfold axis. The similarity o f this hexagonal phase to the hexagonal quasicrystal is shown.