Intermetallic compounds are an interesting class of materials because of their structural properties and their applications e.g. as heterogeneous catalysts. The binary phases Al₉Co₂ (Pearson symbol mP22), Al₁₃Co₄ (oP102) and Al₁₃Fe₄ (mC102) are complex metallic compounds which usually have quite large unit cells. These phases have similar structural motifs like decagonal quasicrystals but are periodic in all three dimensions. Therefore, they are called approximants to the quasicrystals. They allow comparative studies in order to understand whether some properties of quasicrystals arise from the lack of periodicity or from the clusters that are common to all these phases.
Quite recently it has been shown that the intermetallic compound Al₁₃Fe₄ could be a low-cost alternative for conventional catalysts in the semi-hydrogenation of acetylene [1] which is an important reaction in the polyethylene production. Conventional catalysts for heterogeneous catalysis usually consist of finely dispersed particles of noble metals or their alloys on an oxide support material. Intermetallic compounds have a high potential as catalysts as they can be highly active with respect to a specific reaction and show advantages in long-term stability and selectivity. InPd (CsCl prototype structure) is an intermetallic phase which is a promising catalyst material for methanol steam reforming. This reaction is a possibility to produce hydrogen for fuel cells in-situ from methanol. So the problems of storage and transportation of hydrogen could be avoided.
In order to understand the basic mechanisms of the catalysis, a number of characterization methods require large and well-defined single-crystalline samples. For this purpose it is necessary to grow cm³-size crystals.
The Czochralski technique is a well suitable growth method for these different phases. Since Al₉Co₂, Al₁₃Co₄ and Al₁₃Fe₄ cannot be crystallized from congruent melts Czochralski growth was done from Al-rich solutions below the specific peritectic temperature of each phase. To reduce the relatively high vapor pressure of indium, growth of InPd was done from an In-rich solution. The growth from high-temperature solutions requires a couple of special conditions that modify the usual Czochralski technique, e.g. an appropriate temperature program to compensate for the decreasing liquidus temperature and very low pulling rates in the range of 100 µm/h or even lower to avoid second phase inclusions.

[1] M. Armbrüster et al., Nat. Mater. 11 (2012), 690.

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1. Czochralski crystal growth of the intermetallic compound InPd