Early work on Laves phases in East Germany

Initiated by Gustav E.R. Schulze, pioneering experimental and theoretical work on Laves phases was done in Dresden/East Germany after World War II, which was then part of the German Democratic Republic GDR behind the former Iron Curtain. Cold War restrictions, many of the results have not become known to the West. The present overview gives an insight into the compounds dealt with, the properties measured, the features calculated and the conclusions drawn. Starting with concepts of crystal chemistry, like inflated coordination number or maximum density, rules for the formation of Laves phases have been established. One focus of the experimental work was the impact of deviation from stoichiometric composition upon structure and physical properties. Mutual substitution of A and B atoms in AB2 phases was identified as prevalent constitutional defect. Apart from structural studies employing X-ray and neutron diffraction, various physical properties of selected members have been measured, like electrical and thermal conductivity, heat capacity, magnetic susceptibility, thermal expansion, diffusion coefficient, and optical constants. Computations of electron and phonon spectra of selected Laves phases from first principles helped to correct the naïve simple-metal-view upon those metallic solids and to understand physical properties more thoroughly. As another main field of research, studies of the plasticity and real structure of certain Laves phases are reviewed. Macroscopic stress–strain behaviour has been broken down to dislocation dynamics using Orowan’s equation. An important role of Peierls stress as obstacle to dislocation movement has been concluded from that. In addition, changes of dislocation density and geometry within the range of homogeneity were characterized quantitatively. Alloy softening was found with off-stoichiometric compounds due to an elevated density of grown-in dislocations.