Heusler composition

This series has been studied over a wide range (Winkler and Wachtel 1978) and shows a maximum magnetic moment at the Heusler composition (x = 0.25). The magnetic moments and magnetic order depend strongly on the local atomic arrangement. 

Fig. 14. Stress—rupture properties of NiAl alloys and composites compared with superaHoy Renit 80 (77). The Heusler precipitates (ppts) = 50 Ni—25 Al—25X (at. %), where X = a Group 4 (IVB) or Group 5 (VB) element such as Hf. To convert MPa to psi, multiply by 145.

A quantum-mechanical interpretation of Miedema s parameters has already been proposed by Chelikowsky and Phillips (1978). Extensions of the model to complex alloy systems have been considered. As an interesting application we may mention the discussion on the stabilities of ternary compounds presented by de Boer et al. (1988). In the case of the Heusler-type alloys XY2Z, for instance, the stability conditions with respect to mechanical mixtures of the same nominal composition (XY2+Z, X+Y2Z, XY+YZ, etc.) have been systematically examined and presented by means of diagrams. The Miedema s parameters, A t>, A ws1/3, moreover, have been used as variables for the construction of structural maps of intermetallic phases (Zunger 1981, Rajasekharan and Girgis 1983). 

The entropy of mixing has important consequences not only for the simple theories of mixing but also in such areas as solid-solutions where a mixture of two species with a single electroactive common ion can show considerable deviations from the expected linear behavior of formal potential with composition, a result highlighted by Heusler. 

Fig. 33. Dependence on Mn concentration of Kerr rotation spectra of Heusler alloys of a composition Ni3 tMnJCSn. The full lines and dashed lines refer to

Analyzing the dissolution kinetics of alloys in a more general way, Heusler attributed deviations from the ideal behavior in simultaneous alloy dissolution (that is, a composition dependence of the phenomenological rate constants of individual alloy components) to a dissolution mechanism that proceeds from kinks in the steps of low-index planes, the concentration of these... 

Three structure types are found with composition 7533 the PrC02Ga-type, oP8, the YPdjSi-type, oP16, and the MnCujAl (Heusler phase)-type, cF16, discussed with YPdjSn. 

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