Structures, intermetallic

The phase distribution observed in the alloys deposited from AlCb-NaCl is very similar to that of Mn-Al alloys electrodeposited from the same chloroaluminate melt [126 129], Such similarity may also be found between the phase structure of Cr-Al and Mn-Al alloys produced by rapid solidification from the liquid [7, 124], These observations are coincident with the resemblance of the phase diagrams for Cr-Al and Mn-Al, which contain several intermetallic compounds with narrow compositional ranges [20], inhibition of the nucleation and growth of ordered, often low symmetry, intermetallic structures is commonly observed in non-equilibrium processing. Phase evolution is the result of a balance between the interface velocity and... 

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. 

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. 

In another paper (Daams and Villars 1993), the results of a similar classification of the rhombohedral intermetallic structure types were shown. The 195 rhombohe-dral structure types reported in Villars and Calvert (1991) were analysed 51 types had improbable interatomic distances or correspond to oxides with no intermetallic representatives and were excluded. The remaining 144 types (corresponding to 1324 compounds) were considered. It was observed that 14 AET are greatly... 

Several intermetallic phase structures can be described in terms of an assembly of building blocks consisting of a collection of coordination polyhedra. A classification of types of intermetallic structures based on the coordination number, configurations of coordination polyhedra and their method of combination has been given by Kripyakevich (1963). 

Daams, J.L.C. (1995) Atomic environments in some related intermetallic structure types. In Intermetallic Compounds, eds. Westbrook, J.H. and Fleisher, R.L. (John Wiley and Sons Ltd, Chichester), Vol. 1, p. 363. 

Kripyakevich, P.I. (1963) A systematic classification of types of intermetallic structures J. Struct. Chem., 4. 

Several thousand binary, ternary and quaternary intermetallic phases have been identified and their structures determined. In a comprehensive compilation such as that by Villars and Calvert, about 2200 (first edition, 1985) or about 2700 (second edition, 1991) different types of intermetallic structures are described. The specific data concerning about 17 500 different intermetallic phases belonging to the aforementioned structural types are reported in the first edition, and 26 000 in the second edition. 

---