Synthesis and crystal structure of a new Cu₃Au-type ternary phase in the Au–In–Pd system: distribution of atoms over crystallographic positions

Abstract

A new CuAu-type ternary phase (τ phase) is found in the AuPd-rich part of the Au-In-Pd system. It has a broad homogeneity range based on extensive (Pd,Au) and (In,Au) replacement, with the composition varying between AuInPd and AuInPd. The occupancies of the crystallographic positions were studied by single-crystal X-ray diffraction for three samples of different composition. The sites with m-3m symmetry are occupied by atoms with a smaller scattering power than the atoms located on 4/mmm sites. Two extreme structure models were refined. Within the first, the occupation type changes from (Au,In,Pd)(Pd,In) to (Au,Pd)(In,Pd,Au) with an increase in the Au gross content. For the second model, the occupation type (Au,In,Pd)(Pd,Au) remains essentially unchanged for all Au concentrations. Although the diffraction data do not allow the choice of one of these models, the latter model, where Au substitutes In on 4/mmm sites, seems to be preferable, since it agrees with the fact that the homogeneity range of the τ phase is inclined to the Au corner and provides the same occupation type for all the studied samples of different compositions.

Structure and Stability of the Stoichiometric Al3Fe Phase

“…First of all, it is necessary to emphasize that the ordered stoichiometric Al 3 Fe phase was established based on the structural refinement results in the present work. There are two aspects of fact: (1) Different from other metallic phases in Cu 3 Au (FCC lattice) types or other stoichiometric in the Al-Fe like Fe 3 Al (bcc lattice) [41,42], there is no ideal stoichiometric Al 3 Fe that has been synthesized and characterized up until now; (2) previously reported results are all off-stoichiometric Al 3 Fe phases, like Al 5 Fe 2 , Al 13 Fe 4 etc. [1,43].…”