No abstract

There has been considerable recent interest in the high-pressure behavior of silicon carbide, a potential major constituent of carbon-rich exoplanets. In this work, the atomic-level structure of SiC was determined through in situ X-ray diffraction under laser-driven ramp compression up to 1.5 TPa; stresses more than seven times greater than previous static and shock data. Here we show that the B1-type structure persists over this stress range and we have constrained its equation of state (EOS). Using this data we have determined the first experimentally based mass-radius curves for a hypothetical pure SiC planet. Interior structure models are constructed for planets consisting of a SiC-rich mantle and iron-rich core. Carbide planets are found to be ~10% less dense than corresponding terrestrial planets.

Mg-rich olivine (Mg,Fe) 2 SiO 4 , occurs widely in igneous and metamorphic rocks, and is the dominant phase in Earth's upper mantle (Ringwood, 1991). The physical properties of liquid Mg 2 SiO 4 are important for modeling partial melting of the mantle and the behavior of magma oceans (Mosenfelder et al., 2007). In addition, olivine is a common constituent of terrestrial planets (Mustard et al., 2005) and meteorites (Mason, 1963), and is also found in comets (Hanner, 1999), presolar grains (Nguyen & Zinner, 2004), and in accretion disks around young stars (van Boekel et al., 2004). Static-compression experiments have shown that at high pressure and temperature (>1,000 K), (Mg,Fe) 2 SiO 4 adopts a spinelloid structure (wadsleyite) at about ∼14 GPa, and then transforms to a spinel structure (ringwoodite) at ∼18 GPa (Frost, 2008). At 24 GPa, ringwoodite dissociates into (Mg,Fe) SiO 3 , bridgmanite and (Mg,Fe)O, ferropericlase which are expected to be the major phases of Earth's lower mantle. These phase transitions in the (Mg,Fe) 2 SiO 4 system are the primary cause of the ma

The oxo‐Mn(IV) complexes (II) are prepared by electrooxidation of (I) in MeCN containing (NBu4)OH.

Resonance Raman spectroscopy can readily distinguish between oxidation of the porphyrin ring or the metal.