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Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function of the involved elements is often lacking. It is one of the two main goals of this review to summarize the knowledge for some selected respective topics with a certain focus on non-stoichiometric, i.e., non-ideal Laves phases. The second, central goal of the review is to give a systematic overview about the role of Laves phases in all kinds of materials for functional and structural applications. There is a surprisingly broad range of successful utilization of Laves phases in functional applications comprising Laves phases as hydrogen storage material (Hydraloy), as magneto-mechanical sensors and actuators (Terfenol), or for wear- and corrosion-resistant coatings in corrosive atmospheres and at high temperatures (Tribaloy), to name but a few. Regarding structural applications, there is a renewed interest in using Laves phases for creep-strengthening of high-temperature steels and new respective alloy design concepts were developed and successfully tested. Apart from steels, Laves phases also occur in various other kinds of structural materials sometimes effectively improving properties, but often also acting in a detrimental way.

The metallic interstitial nitride Ni(3)N was prepared from Ni(NH(3))(6)Cl(2) and NaNH(2) in supercritical ammonia (p(NH(3)) approximately 2 kbar) at 523 K. Its previously reported crystal structure, as determined from X-ray powder data, was confirmed by neutron powder diffraction: Ni(3)N crystallizes in the hexagonal epsilon-Fe(3)N-type structure (P6(3)22, Z = 2, a = 4.6224 A and c = 4.3059 A at room temperature). The N atoms on the octahedral sites of an hcp arrangement of Ni show virtually complete occupational order at ambient temperatures, which is preserved up to its thermal decomposition at T approximately 600 K. This behavior is in marked contrast to that of the isotypic iron nitride, epsilon-Fe(3)N, which shows reversible partial disordering within the same range of temperatures. Possible reasons for the different behaviors of the two nitrides epsilon-Fe(3)N and Ni(3)N are discussed.