High-pressure phases of CuI studied by¹²⁹I-Mössbauer spectroscopy

Abstract

The results of an¹²⁹I-Mössbauer study of the high-pressure phases of CuI at 4.2 K and for external pressures up to 71 kbar are reported. The isomer shiftS and the electric quadrupole interactionE _q are found to undergo larges discontinuities at the crystallographic phase-transition pressures of ≅18 kbar from zinc-blence to rhombohedral structure and at ≅46 kbar from rhombohedral to tetragonal. The pressure coefficients of these hyperfine parameters are significantly different for the three phases (zinc-blende; rhombohedral; tetragonal) dS/dP=−3.3; =+1.5; =2.5×10⁻³ mm/s/kbar; dE _q/dP=0.0; =−0.92;=+0.31 Mc/s/kbar. These results cannot be explained in terms of a simple molecular-orbital picture; instead, they reflect pressure-induced variations of the halogen-p/metal-d hybridization in the valence bands of the various phases of CuI.