Analysis of Gas-Phase Clusters Made from Laser-Vaporized Icosahedral Al−Pd−Mn
An icosahedral Al-Pd-Mn quasicrystal sample is laser vaporized to form metal clusters by gas aggregation. The clusters are subsequently laser ionized and mass analyzed in a time-of-flight mass spectrometer. The mass spectra show cluster compositions which are qualitatively similar to that of the sample. This is consistent with a kinetically controlled cluster growth process. Cluster thermodynamic stability is probed by multiphoton ionization/fragmentation, which induces primarily Al and Mn loss. The resulting spectra are composed of a series of Pd-rich Al-Pd clusters. The average cluster composition is 60 (′1)% Pd. This composition is close to a known eutectic in the Al-Pd system. When manganese is seen on these clusters, it is always in units of Mn 3 . These results are discussed in terms of relative binding strengths in the Al-Pd-Mn alloy system.
Stable clusters in quasicrystals: fact or fiction?
Undoubtedly, the cluster approach has been a very successful and useful tool for describing and modelling the structure of quasicrystals. However, a number of unanswered questions remain as to how stable these clusters are, in what way do they contribute to the stability of quasicrystals and what physical properties they have. In the following, the different ways in which the term cluster is used are summarised.
Mechanical properties of large quasicrystals in the Al–Cu–Li system
Following the report of Dubost et al.1, the synthesis and detailed growth characteristics of the quasicrystalline phase in the Al–Cu–Li system were recently documented2. Here we have grown large (∼3 mm) grains as well as orientated grains of the quasicrystals and have studied their mechanical properties. On account of the quasicrystals being brittle, we have employed successfully an indentation technique3–7, normally used for brittle ceramics, to determine hardness and fracture toughness. Here we report the technique used and the values obtained.