Campus Units

Chemistry

Document Type

Article

Publication Date

2013

Journal or Book Title

Inorganic Chemistry

Volume

52

First Page

6603

Last Page

6609

DOI

10.1021/ic400626x

Abstract

Sr3Au8Sn3 was synthesized through fusion of a stoichiometric amount of pure metals at 800 °C and annealing treatments at lower temperatures. Single-crystal X-ray diffraction analyses revealed that Sr3Au8Sn3 has a La3Al11-type Immm structure (a = 4.6767(8) Å, b = 9.646(2) Å, c = 14.170(2) Å, Z = 2) if annealed at 550 °C and above but a Ca3Au8Ge3-type structure (Pnnm, a = 9.6082(8) Å, b = 14.171(1) Å, c = 4.6719(4) Å, Z = 2) if annealed at 400 °C. The transition occurs at about 454 °C according to DTA data. Both structures feature columns of Sr-centered pentagonal and hexagonal prisms of Au and Sn stacked along the respective longest axial directions, but different “colorings” of the polyhedra are evident. In the high-temperature phase (Immm) all sites shared between the two prisms adopt 50:50 mixtures of Au/Sn atoms, whereas in the low-temperature phase (Pnnm) Au or Sn are completely ordered. A Klassengleiche group–subgroup relationship was established between these two structures. LMTO-ASA calculations reveal that ΔE for the disorder-to-order transformation on cooling is driven mainly by optimization of the Au–Au and Au–Sn bond populations around the former mixed Au/Sn sites, particularly those with extremely short bonds at the higher temperature. These gains also overcome the smaller effect of ordering on the entropy decrease.

Comments

This is an article from Inorganic Chemistry 52 (2013): 6603, doi: 10.1021/ic400626x. Posted with permission.

Copyright Owner

American Chemical Society

Language

en

File Format

application/pdf

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