Intermetallic crystal chemistry

In another chapter concerning the intermetallic crystallochemistry (Chapter 7), a number of selected structural prototypes are described presenting some of their typical features and commenting on their distribution among different types of alloys. Attention is especially given to relationships between different prototype structures, and examples of their possible grouping in structural families are underlined. This chapter, therefore, could possibly be used as a first draft of a gazetteer of intermetallic structure types and could be considered as an introduction (partial and provisional indeed ) to the descriptive systematics of intermetallic crystal chemistry. 

Some details and questions about these points will be discussed in the next paragraphs. These will then be used for a description of selected common phases and a presentation of a few characteristic features of intermetallic crystal chemistry. 

I. S. Yvich, N. F. Chaban, Abstracts, Conference on the Crystal Chemistry of Intermetallic Compounds, Tersizy. Dokl., L vov, October 1989, p. 46. 

Another characteristic point is the special attention that in intermetallic science, as in several fields of chemistry, needs to be dedicated to the structural aspects and to the description of the phases. The structure of intermetallic alloys in their different states, liquid, amorphous (glassy), quasi-crystalline and fully, three-dimensionally (3D) periodic crystalline are closely related to the different properties shown by these substances. Two chapters are therefore dedicated to selected aspects of intermetallic structural chemistry. Particular attention is dedicated to the solid state, in which a very large variety of properties and structures can be found. Solid intermetallic phases, generally non-molecular by nature, are characterized by their 3D crystal (or quasicrystal) structure. A great many crystal structures (often complex or very complex) have been elucidated, and intermetallic crystallochemistry is a fundamental topic of reference. A great number of papers have been published containing results obtained by powder and single crystal X-ray diffractometry and by neutron and electron diffraction methods. A characteristic nomenclature and several symbols and representations have been developed for the description, classification and identification of these phases. 

Iandelli, A. and Palenzona, A. (1979) crystal chemistry of intermetallic compounds. In Handbook on the Physics and Chemistry of Rare Earths, eds. Gschneidner Jr., K.A. and Eyring, L. (North-Holland, Amsterdam), Vol.2, p. 1. 

Notes on the alloy crystal chemistry of the 6th group metals. A selection of the intermetallic phases, and of their structures, formed by Cr, Mo and W is shown in Table 5.35. Attention has been given in this list to the presence of several tetrahedrally close-packed alloys, often corresponding to ranges of solid solutions. 

The two authors of the book, Prof. Ferro and Saccone, had been close scientific collaborators for many years. I first came to know them when, in the early 1990s, I was advised to invite them to contribute a chapter on intermetallic compounds to the fourth edition of my Physical Metallurgy, which duly appeared in 1996. Since then I have come to appreciate fully the remarkable team of solid-state chemists built up in Genoa by Prof. Ferro and Saccone. Their approach to the borderlands of crystal chemistry and metallurgy is unique and very impressive. This book, Intermetallic Chemistry, which has been several years in preparation, encapsulates their joint approach, and I regard its publication as a fitting memorial to a truly remarkable man. 

Lebedev, V.A., Pyatkov, V.I., Ushenin, S.N., 1983. Thermodynamic properties and phase composition of the alloys of the La-Sb system. In IV All-Union Conference on the Crystal Chemistry of Intermetallic Compounds, Abstracts, Lvov, p. 206. 

Pavlyuk, V.V. 1993. Synthesis and crystal chemistry of the intermetallic compounds of lithium, Dr.Sc. Chemistry Thesis, Abstracts, L viv (L viv State University, L viv) pp. 1—46. 

A. IandeUi and A. Palenzona, Crystal chemistry of intermetallic compounds 1... 

Bulanova M., Tretyachenko L., Mileshevich K. et al. (2002) Joint influence of zirconium and silicon on the structure and properties of Ti and Ti-Al alloys. In Coll. Abstracts of the VIII Int. Conf. on Crystal Chemistry of Intermetallic Compounds, Lviv, Ukraine, p. 40. 

Alloy systems have been known to man since the Bronze Age. It is, however, only in recent times that they have been the subject of systematic studies, and in these studies no tool has proved more powerful than the technique of crystal structure analysis. Indeed, the extension of our knowledge and understanding of the properties of intermetallic systems to which it has given rise is one of the greatest achievements of crystal chemistry. Prior to the application of X-ray methods, the investigation of the properties of alloy systems was confined principally to observations of their behaviour in the liquid state, and the behaviour of the metal as a solid could be determined only by inference from these observations. Transitions in the solid state and the effect of mechanical or heat treatment could not, of course, be observed in this way, and for information on these properties the microscope and other purely physical methods had to be invoked. Even so, these methods were all more or less indirect, and it is only since the application of X-ray analysis that it has been possible to investigate directly in the solid state, under the precise conditions which are of technical interest and without damage to the specimen, the exact positions of all the atoms in the structure, and so to refer to their ultimate cause the physical and chemical properties of the alloy. 

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