Electron-poor SrAuxIn4−x (0.5⩽x⩽1.2) and SrAuxSn4−x (1.3⩽x⩽2.2) phases with the BaAl4-type structure

Solid solutions SrAuxIn4−x (0.5⩽x⩽1.2) and SrAuxSn4−x (1.3⩽x⩽2.2) have been prepared at 700 °C and their structures characterized by powder and single-crystal X-ray diffraction. They adopt the tetragonal BaAl4-type structure (space group I4/mmm, Z=2; SrAu1.1(1)In2.9(1), a=4.5841(2) Å, c=12.3725(5) Å; SrAu1.4(1)Sn2.6(1), a=4.6447(7) Å, c=11.403(2) Å), with Au atoms preferentially substituting into the apical over basal sites within the anionic network. The phase width inherent in these solid solutions implies that the BaAl4-type structure can be stabilized over a range of valence electron counts (vec), 13.0–11.6 for SrAuxIn4−x and 14.1–11.4 for SrAuxSn4−x. They represent new examples of electron-poor BaAl4-type compounds, which generally have a vec of 14. Band structure calculations confirm that substitution of Au, with its smaller size and fewer number of valence electrons, for In or Sn atoms enables the BaAl4-type structure to be stabilized in the parent binaries SrIn4 and SrSn4, which adopt different structure types.