Electron concentration and phase stability in binary alloys in–pb and hg–sn under high pressure

Abstract

High-pressure diffraction studies of binary alloys provide information on what factors control the formation of solid solutions and intermetallic phases, their composition ranges and crystal structure. We have investigated effects of pressure on binary alloys In–Pb with 10, 15 and 22 at.% Pb and Hg–Sn of equiatomic composition with diamond anvil cells using synchrotron radiation up to pressures of 30 GPa under pressure, In–Pb alloy with 10 at.% Pb undergoes a phase transition from one face-centred tetragonal (fct) phase to another fct phase through a two-phase co-existence region from 7 to 20 GPa, with a discontinuous jump in the axial ratio c/a from > 1 to < 1. The α-Hg phase with a rhombohedral distortion of a face-centered cubic structure, known to be stable only up to 3.7 GPa in pure Hg, is found here to be stabilised by the alloying of 5–10 at.% Sn up to pressures of at least 30 GPa. This rhombohedral phase, hR1-(Hg), reveals strong anisotropy on compression with an increase in c/a from 1.99 to 2.25 in the pressure range of its stability from 2.6 to 29.9 GPa. Tetragonal distortions in the In–Pb alloys, stabilisation of the hR1-(Hg) phase by alloying Hg with Sn and range of solubility of Sn in α-Hg are discussed within the concept of the Brillouin zone–Fermi sphere interactions.

Keywords:

• Phase stability
• High pressure
• Hume-Rothery phases
• Binary alloys

Acknowledgements

The financial support by the Russian Foundation for Basic Research under the grant number 04-02-17343 is gratefully acknowledged.