Pressure evolution of the structure of

The structural features of the ammoniated (NH3)K3C60 fulleride are studied by synchrotron X-ray powder diffraction as a function of pressure to 6.7 GPa. A superstructure appears at ~1 GPa as a result of orientational ordering of both the C60 and K+-NH3 units (orthorhombic symmetry, space group Fddd). The pressure evolution of the lattice constants reveals a highly compressible, strongly anisotropic structure. The centre-to-centre interfullerene separations of ~10.40 Åin the basal plane are comparable to those in the superconducting cubic analogue, RbCs2C60 and evidently sufficiently short to drive the system superconducting, despite its low crystal symmetry

Modern and past volcanic degassing of iodine

International audienceWe have monitored iodine degassing from a melt to a water vapor during decompression (i.e. magma ascent). Experimentshave been performed by combining diamond anvil cells experiments with synchrotron X-rays fluorescence analysis. Partitioncoefficients DIfluid/melt measured for a pressure and temperature range of 0.1–1.8 GPa and 500–900 C, range from 41 to 1.92,values for room conditions DIfluid/glass (quenched samples) are equal to or higher than 350. We show that iodine degassing withwater is earlier and much more efficient than for lighter halogen elements, Cl and Br. Iodine is totally degassed from the silicatemelt at room conditions. By applying these results to modern volcanology, we calculate an annual iodine flux for subductionrelated volcanism of 0.16–2.4 kt yr1. We suggest that the natural iodine degassing may be underestimated, havingpossible consequences on the Earth’s ozone destruction cycle. By applying this results to the Early Earth, we propose a processthat may explain the contrasted signature of I, Br and Cl, strongly depleted in the bulk silicate Earth, the most depletedbeing iodine, whereas fluorine is almost enriched. The Earth may have lost heavy halogen elements during an early waterdegassing process from the magma ocean