Phase transitions under high pressure inbinary Sn alloys (with In, Hg and Ga)

Abstract

Crystal structures of binary alloys of Sn with In, Hg and Ga werestudied under pressure with diamond-anvil cells andenergy-dispersive diffraction of synchrotron radiation. The ambient-pressure simple hexagonal (sh)phase in In-Sn alloys becomes unstable under pressure above 13 GPaand decomposes into the mixture of two phases: the body-centredtetragonal (bct) phase and hexagonal close-packed (hcp)phase with compositions ~15 and ~25 at.% In,respectively. The hcp/bct phase boundary shifts towardsSn with increasing pressure. A similar behaviour was found for thesh phase in Hg-Sn alloys, where the hcp phase occurs athigher pressure. Another bct phase with an axial ratiosimilar to that in In occurs under pressure in the Hg-Sn alloysystem at the composition ~50/50.A sh phase was also found in the Ga-Sn alloy systemnear 80 at.% Sn at pressures above 11 GPa after heating to150 °C, showing a similarity to the ambient-pressuresh phases in In-Sn and Hg-Sn alloys.Structural sequences of phases in binary alloys are discussedwith respect to the valence electron concentration of thealloys, taking into account the results of the present andprevious structural high-pressure studies on Sn-based andrelated alloys.