3. Crystal Structure of Heusler Compounds

Heusler compounds are promising materials in many fields of contemporary research. The spectrum of their possible applications ranges from magnetic and magneto-mechanical materials over semiconductors and thermoelectrics to superconductors. An important feature of the Heusler compounds is the possibility of controlling the valence electron concentration by partial substitution of elements. On the other hand, the properties also depend on the degree of ordering of the crystal structure. In general, Heusler compounds crystallize in the Cu₂MnAl-type structure but in many cases certain types of disorder are observed. In this chapter, a detailed description of the crystal structure as well as different types of atomic disorder are given. Furthermore, the relationship of the chemical ordering and the spin polarization is discussed and useful experimental methods for the structural analysis of Heusler compounds are presented.