The high-pressure structure of (1-x)Na Bi TiO -xBaTiO at the morphotropic phase boundary.

The pressure-induced structural changes in the perovskite-type (ABO ) ferroelectric solid solution (1-x)Na Bi TiO -xBaTiO (NBT-xBT) at the morphotropic phase boundary (MPB) ( ) have been analyzed up to 12.3 GPa by single-crystal x-ray diffraction with synchrotron radiation. A pressure-induced phase transition takes place between 4.

On the identification of hyperhydrated sodium chloride hydrates, stable at icy moon conditions.

Sodium chloride is expected to be found on many of the surfaces of icy moons like Europa and Ganymede. However, spectral identification remains elusive as the known NaCl-bearing phases cannot match current observations, which require higher number of water of hydration. Working at relevant conditions for icy worlds, we report the characterization of three "hyperhydrated" sodium chloride (SC) hydrates, and refined two crystal structures [2NaCl·17HO (SC8.

Host-Guest Hydrogen Bonding in High-Pressure Acetone Clathrate Hydrates: Single-Crystal X-ray Diffraction Study.

The phenomenon of host-guest hydrogen bonding in clathrate hydrate crystal structures and its effect on physical and chemical properties have become subjects of extensive research. Hydrogen bonding has been studied for cubic (sI and sII) and hexagonal (sH) binary clathrates, while it has not been addressed for clathrate structures that exist at elevated pressures. Here, four acetone hydrate clathrates have been grown at high-pressure and low-temperature conditions.

Estimating the viscosity of volcanic melts from the vibrational properties of their parental glasses.

The numerical modelling of magma transport and volcanic eruptions requires accurate knowledge of the viscosity of magmatic liquids as a function of temperature and melt composition. However, there is growing evidence that volcanic melts can be prone to nanoscale modification and crystallization before and during viscosity measurements. This challenges the possibility of being able to quantify the crystal-free melt phase contribution to the measured viscosity.

Iron Plaque at Rice Roots: No Barrier for Methylated Thioarsenates.

Iron (hydr)oxide coating at rice roots, so-called iron plaque (IP), is often an important barrier for uptake of inorganic oxyarsenic species and their accumulation in rice grains. Sorption of methylated thioarsenates, which can co-exist with inorganic and methylated oxyarsenates in paddy soils, was not studied yet, even though these toxic species were detected in xylem and grains of rice plants before. Hydroponic experiments at pH 6.

Deep magma ocean formation set the oxidation state of Earth's mantle.

The composition of Earth's atmosphere depends on the redox state of the mantle, which became more oxidizing at some stage after Earth's core started to form. Through high-pressure experiments, we found that Fe in a deep magma ocean would disproportionate to Fe plus metallic iron at high pressures. The separation of this metallic iron to the core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species.

Differentiating between long and short range disorder in infra-red spectra: on the meaning of "crystallinity" in silica.

Local atomic disorder and crystallinity are structural properties that influence greatly the resulting chemical and mechanical properties of inorganic solids, and are used as indicators for different pathways of material formation. Here, these structural properties are assessed in the crystals of quartz based on particle-size-related scattering processes in transmission infra-red spectroscopy. Independent determinations of particle size distributions in the range 2-100 μm of a single crystal of quartz and defective quartz with highly anisotropic micro-crystallites show that particle sizes below the employed wavelength (approx 10 μm) exhibit asymmetric narrowing of absorption peak widths, due to scattering processes that depend on the intra-particle structural defects and long range crystallinity.

Hidden Oceans? Unraveling the Structure of Hydrous Defects in the Earth's Deep Interior.

High-pressure silicates making up the main proportion of the earth's interior can incorporate a significant amount of water in the form of OH defects. Generally, they are charge balanced by removing low-valent cations such as Mg. By combining high-resolution multidimensional single- and double-quantum H solid-state NMR spectroscopy with density functional theory calculations, we show that, for ringwoodite (γ-MgSiO), additionally, Si vacancies are formed, even at a water content as low as 0.

Stability of Fe,Al-bearing bridgmanite in the lower mantle and synthesis of pure Fe-bridgmanite.

The physical and chemical properties of Earth's mantle, as well as its dynamics and evolution, heavily depend on the phase composition of the region. On the basis of experiments in laser-heated diamond anvil cells, we demonstrate that Fe,Al-bearing bridgmanite (magnesium silicate perovskite) is stable to pressures over 120 GPa and temperatures above 3000 K. Ferric iron stabilizes Fe-rich bridgmanite such that we were able to synthesize pure iron bridgmanite at pressures between ~45 and 110 GPa.

Pressure-induced hydrogen bond symmetrization in iron oxyhydroxide.

Under high pressures the hydrogen bonds were predicted to transform from a highly asymmetric soft O-H···O to a symmetric rigid configuration in which the proton lies midway between the two oxygen atoms. Despite four decades of research on hydroxyl containing compounds, pressure induced hydrogen bond symmetrization remains elusive. Following single crystal x-ray diffraction, Mössbauer and Raman spectroscopy measurements supported by ab initio calculations, we report the H-bonds symmetrization in iron oxyhydroxide, FeOOH, resulting from the Fe(3+) high-to-low spin crossover at above 45 GPa.

A novel gas-loading system for mechanically closing of various types of diamond anvil cells.

Loading of gases in diamond anvil cells is a complicated but necessary task to obtain hydrostatic conditions for high-pressure measurements. A simple in operation, safe, and universal gas-loading system has been designed and constructed. Innovations were introduced to simplify the loading procedure up to the "three-button" mode.