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

Evgeniya A Ptashkina; Elizaveta G Kabanova; Anna I Tursina; Alexandr V Yatsenko; Victor N Kuznetsov

doi:10.1107/S2053229618001973

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

Acta Crystallogr C Struct Chem. 2018 Mar 1;74(Pt 3):295-299. doi: 10.1107/S2053229618001973. Epub 2018 Feb 14.

Authors

Evgeniya A Ptashkina¹, Elizaveta G Kabanova¹, Anna I Tursina¹, Alexandr V Yatsenko¹, Victor N Kuznetsov¹

Affiliation

¹ Department of Chemistry, Moscow State University, 119991 Moscow, Russian Federation.

PMID: 29504557
DOI: 10.1107/S2053229618001973

Abstract

A new Cu₃Au-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 Au_17.7In_25.3Pd_57.0 and Au_50.8In_16.2Pd_33.0. 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)₃(Pd,In) to (Au,Pd)₃(In,Pd,Au) with an increase in the Au gross content. For the second model, the occupation type (Au,In,Pd)₃(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.

Keywords: Au–In–Pd ternary phase; Cu3Au structure type; VEC; crystal structure; gold; indium; intermetallic compound; mixed occupancy; palladium; valence electronic concentration.