Structural Principles of Giant Cells

Abstract

It is a curious coincidence that the paper by Linus Pauling,¹ which first described the crystal structure of an intermetallic compound, presented simultaneously one of the most complicated structure problems that lay ahead. In this paper Pauling discussed the atomic arrangement of Mg₂Sn, which has the calcium fluoride structure, and also gave a brief account of an X-ray diffraction study of crystals of NaCd₂. The diffraction patterns of these crystals were so complicated, however, that it was not then possible to assign indices with certainty to many of the spots. The unit of structure was later² reported to be a cube that has an edge length slightly over 30Ǻ and contains about 384 sodium atoms and 768 cadmium atoms. The space group is Fd3m (O⁷ _h) . Thus, we see that the existence of this most complex compound has been known for U5 years, ever since the first structure determination of an intermetallic compound was published.