Phase transition in a tetragonal In90Pb10 alloy under high pressure:: a switch from c/a > 1 to c/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.% Ph undergoes underpressure 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.% Ph with c/a < 1 at ambient pressure show only a slight decrease in cla 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.