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Phonon dispersion ω(q) and phonon density of states g(ω) of the high-pressure rocksalt phase of InN are calculated ab initio, at different pressures, using the density functional perturbation theory. Born effective charge e ∗ T , LDA values of dielectric con- stant ∞ and of the electronic gap E g are obtained as well. Building on the theoretical knowledge of phonon frequencies and their evolution with pressure, we attempt to interpret the set of six bands found previously in Raman spectra of epitaxial layers and of InN-nanowires.

International audience; We report a combined study of the structural and electronic properties of the spinel-type semiconductor MnIn2S4 under high pressures by means of X-ray diffraction (ADXRD), X-ray absorption (XAS), and op- tical absorption measurements. The three techniques evidence a reversible structural phase transition near 7 GPa, that according to ADXRD measurements is to a double-NaCl structure. XAS measurements evi- dence predominant tetrahedral coordination for Mn in the spinel phase that does not noticeably change with increasing pressure up to the phase transition. XAS measurements indicate that the static disorder in- creases considerably when the sample reverts from the double-NaCl phase to the spinel phase. Optical ab- sorption measurements show that the direct gap of MnIn2S4 exhibits a nonlinear behaviour with a positive pressure coefficient at pressures below 2.5 GPa and a negative pressure coefficient between 2.5 and 7 GPa. The pressure behavior of the bandgap seems to be affected by the defect concentration. The dou- ble-NaCl phase also exhibits a bandgap with a negative pressure coefficient.

X-ray absorption spectroscopy (XAS) provides information on the local environment of a given atom species and therefore is very sensitive to pressure-induced transformation, in particular when coordination changes occur. This technique allows to determine with a good accuracy the onset of phase transformations. Combined with X-ray diffraction, XAS allows to follow the evolution of the structural parameters under high pressure. The low energy part of the spectrum, related to the symmetry around the absorbing atom, is a fingerprint of the structure and can be compared to simulated spectra using multiple scattering calculations. For amorphous samples X-ray absorption spectroscopy remains a very efficient tool to study the local order in the sample. XAS at high pressure and high temperature using large volume cells is now available. Preliminary results on melting of Ge and CdTe are presented.

CuInS2 and CuInSe2 chalcopyrites have been studied up to 29 GPa in a diamond anvil cell by energy dispersive X-ray diffraction (EDX) using synchrotron radiation. Phase transitions have been observed at 9.5 and 7.6 GPa and the high-pressure phases have been indexed as cubic. The pressure dependence of the volume per formula unit has been fitted with a first-order Murnaghan equation of state. The bulk moduli are 75 and 72 GPa for the chalcopyrite phases and 123 and 114 GPa for the cubic phases of CuInS2 and CuInSe2, respectively. The volume reduction at the transition pressure is roughly 10%. The recovered phases are quite different from the initial ones. For CuInSe2 it is of the zincblende type, for CuInS2 it is an amorphous phase. Thus, the pressure-induced phase changes are not reversible.

The only member of the II–III2–VI4 semiconductor family with layered structure is ZnIn2S4. At ambient conditions several polytypes of this compound have been reported. Energy dispersive X-ray diffraction of ZnIn2S4 has been realized at high pressure up to 18 GPa. The structure of this polytype IIIa-ZnIn2S4 is rhombohedral with space group R3-m. It consists of a close-packed arrangement of S atoms, with Zn and half of the In atoms randomly distributed on tetrahedral sites, and the other half of the In atoms located on octahedral sites. The hexagonal axes are a = (3.873 ± 0.002) A and c = (37.067 ± 0.004) A (V = 482 A3, Z = 3). No phase transition has been observed between 0 and 18 GPa. The bulk modulus, obtained by fitting the data to a first-order Murnaghan equation of state is B = (82 ± 8) GPa.