The fcc-bcc Bain path in In-Sn and related alloys at ambient and high pressure.

Experimental high-pressure structural studies on an In-Sn alloy containing 8 at.% Sn reveal an isostructural transition of a face-centered tetragonal phase at pressures above 15 GPa with a switch of the axial ratio from c/a>1 to c/a<1. Such tetragonal phases in binary alloys based on In and Sn are analyzed in relation to the Bain path, i.e. a transformation between a face-centered cubic (fcc) and a body-centered cubic (bcc) structure. Variation of the axial ratio c/a in these phases correlates with the average number of valence electrons per atom in an alloy. A common Bain path from fcc to bcc is discussed within a nearly-free-electron model of Brillouin-zone-Fermi-sphere interactions.