On the growth of icosahedral Al–Pd–Mn quasicrystals from the ternary melt

Abstract

Abstract Icosahedral Al71Pd21,Mn8 quasicrystals have been grown from the ternary melt via a ‘self-flux’ technique. The nucleation is exceptionally well controlled, and individual grains can have masses of up to almost 30 g (limited only by the dimensions of the growth crucible). The quasicrystals grown by this technique are readily separated from the melt by decanting and clearly manifest a dodecahedral morphology with pentagonal facets. X-ray and electron-diffraction data indicate a remarkably well-ordered structure. with a correlation length of over 1000 A. The magnetic susceptibility has a temperature-independent diamagnetic component and a temperature-dependent paramagnetic term. For temperatures greater than approximately 60 K, the paramagnetic term follows a Curie-Weiss temperature dependence characterized by an average effective moment of 0.62 ± 0.02μB/Mn and a Weiss temperature of −12.8 ± 0.1 K. Deviations from the Curie-Weiss temperature dependence for temperatures less than approximately 60 K may be due to the formation of local (short range) magnetic correlations. The electrical resistivity has a broad maximum at approximately 90 K and a room-temperature value of 1.57 ± 0.05 mΩ cm. We note that the previously observed empirical trend that a very high resistivity is associated with the highest quality Al–Pd–Mn quasicrystals does not seem to be in general true and that these high-quality (as demonstrated by X-ray and electron diffraction) ‘flux-grown’ samples have a relatively low room-temperature resistivity. In addition to the ternary icosahedral Al–Pd–Mn quasicrystals, a novel pseudo-quaternary icosahedral quasicrystal, Al67,Ga4Pd21,Mn8, is described.