Phase transition in a tetragonal In90Pb10alloy under high pressure: a switch fromc/a> 1 toc/a< 1

The effect of pressure on tetragonal In–Pb alloys with 10, 15, and 22 at.% Pb has been studied up to pressure 30 GPa with diamond anvil cells using synchrotron radiation. The In-type face-centred tetragonal phase of the In alloy with 10 at.% Pb undergoes under pressure a phase transition with a discontinuous jump of the axial ratio from c / a > 1 to c / a < 1 via a two-phase region from 7 to 20 GPa. The tetragonal phases of the In alloys with 15 and 22 at.% Pb with c / a < 1 at ambient pressure show only a slight decrease in c / a with pressure increase. The correlation of the axial ratio with the alloy content and its change with pressure in In alloys and In itself are attributed to Brillouin-zone–Fermi-sphere interactions.