Single crystal growth of solid solutions from the Ga-Pd-Sn system for basic research in heterogeneous catalysis

Abstract Intermetallic compounds in the binary Ga-Pd system have proved to be superior as catalysts in the semi-hydrogenation of acetylene. Partial substitution of Ga by Sn even increases the activity. In order to study elementary processes of catalytic reactions, well-oriented surfaces of single-crystalline slaps are needed, i.e. single crystal growth is a prerequisite. For the first time, solid/liquid equilibria including the solid solutions Ga1-xSnxPd and Ga1-xSnxPd2 were studied. Based on these findings single crystal growth of the two solid solution series succeeded using the Czochralski method from (Ga,Sn)-rich solutions. Inclusion-free single crystals of a few cm3 in size could be obtained. Due to different crystal structures of the end members, Sn substitution in Ga1-xSnxPd is restricted to x ≈ 0.15 in the cubic phase. Although a complete solid solution range for Ga1-xSnxPd2 has been reported by Armbruster et al. (2018), mixed crystals of the 1:2 phase can be grown from a native ternary melt only up to approx. x = 0.54 due to missing solid/liquid equilibria at a higher ratio of Sn substitution for Ga.