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Mg1–yScyZn2: Limited Sc/Mg Alloying between Laves Phase MgZn2 and ScZn2 – What Drives ScZn2 into a High-Pressure Phase?

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  • Dedicated to Professor John D. Corbett on the occasion of his 85th birthday

Abstract

A series of solid solutions between the MgZn2 and ScZn2 isostructural Laves phases at 400 °C was synthesized by fusion of stoichiometric metals by conventional solid-state high-temperature means. X-ray diffraction analyses revealed that the alloys remain in space group P63/mmc, with a = 5.228–5.249 Å and c = 8.532–8.487 Å. The lattice parameters of the solid solution exhibit anisotropic variations: a increases and c decreases with increased starting Sc content (x) inMg1–xScxZn2. The anisotropic changes correspond to the variations of bond lengths in the ab plane and the interlayer bonds in c. Under the applied reaction conditions, the maximum Sc content was estimated to be ymax ≈ 0.47–0.50 in the formula of Mg1–yScyZn2. Theoretical calculations on a hypothetical ScZn2 model extrapolated for normal pressure revealed that it had higher density-of-states (DOS) and evident Zn–Zn antibonding states at the Fermi energy, meaning that high pressure is necessary to counteract the internal stress resulting from antibonding states.

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