PHASE-TRANSITIONS IN INSB AT PRESSURES UP TO 5-GPA

The structural phase transitions in InSb at pressures up to 5 GPa at room temperature have been reexamined by angle-dispersive powder-diffraction techniques on a synchrotron source using an image-plate area detector. Two distinct behaviors have been found: (1) the cubic zinc-blende phase (P1) transforms at approximately 2.1 GPa to a mixture of a tetragonal phase (P2) and an orthorhombic phase (P3), which then transforms to nearly single-phase P3 before recrystallizing to another orthorhombic phase (P4) at the same or only a slightly higher pressure; or (2) P1 transforms directly to P4 at approximately 3.0 GPa. P2 is previously unobserved at room temperature. It has a beta-tin structure (but it is not the InSb-II phase) and appears not to be long-range site ordered. P3 is the InSb-II phase, which is now shown to be orthorhombic and site ordered. P4 is the InSb-IV phase, but it is shown to have many previously unobserved superlattice reflections. P4 is also site ordered. The three phases P2, P3, and P4 appear to account for all previous clear results on InSb at room temperature in this pressure range, and it is shown that the long-accepted P-T phase diagram is incorrect.