Quasicrystalline Films and their Amorphous Precursors
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Quasicrystalline Films and their Amorphous Precursors Roland Haberkern, Jose Barzola-Quiquia, Caroline Madel, and Peter Häussler Technische Universität Chemnitz, Institut für Physik, 09107 Chemnitz, GERMANY ABSTRACT Binary and ternary aluminum based amorphous precursor films have been prepared by the sequential-flash evaporation technique in the case of Al-Mn, Al-Fe, Al-Cu-Fe and Al-Pd-Mn and by co-sputtering in the case of Al-Pd-Re. For well adjusted compositions and an appropriate heat treatment films can be transformed into polycrystalline single phased quasicrystals for all of the systems mentioned above. The transition can be monitored by in situ measurements of electronic transport properties. The structure factors as a function of composition and annealing state has been measured by electron diffraction. They show a unique behavior if the composition is chosen to that of the related quasicrystal. For high annealing states of the amorphous phase the structure factor becomes more intense at the peak positions of the following i-phase. This is interpreted as a unique radial near- and medium-range order of both the i-phase and its amorphous precursor. The final transformation into the quasicrystal is sharp for Al-Cu-Fe and is broad in the case of Al-Pd-Mn and Al-Pd-Re. The transport properties of the resulting single phased films are similar to that of the related bulk samples and allow systematic studies as a function of composition. Some of the i-Al-Pd-Re films are on the insulating side of the metal-insulator transition.
INTRODUCTION The properties of thermodynamically stable Al-based quasicrystals are non-metallic and may be useful for technical applications. Especially mechanical properties like the huge hardness and a small friction coefficient might be of technical interest as they are combined with a high chemical stability [1,2]. But at not too elevated temperatures quasicrystals are brittle. Therefore, applications of quasicrystals as thin films or coatings will be much more likely than as bulk materials. Some efforts have been made to produce such films by different methods like plasma spraying [3] in the case of thick films, or PVD methods [4] in the case of thin films, respectively. Here, we report on a method which uses the crystallization from their amorphous precursors. Recently we could show [5] that high quality single phased qc-films can be obtained by means of a short-term annealing at temperatures much lower than normally needed to remove crystalline remains from a peritectic solidification of bulk materials by a fast solidification as melt-spinning. Additionally, the crystallization from the amorphous (a-) phase (which is structurally similar to the liquid (l-) phase) is fully within the solid state. This allows to monitor the transition to the icosahedral (i-) phase and subsequently to optimize the heat treatment. A reason for the sharp transition between a- and i-phase at low-temperature may be the long debated local similarity between the l-, a- and the i-phase which where proposed to ex
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