For more than 20 years, most of the technological achievements for the realization of positive electrodes for practical rechargeable Li battery systems have been devoted to transition metal oxides such as LixMO2 (M = Co, Ni, Mn), LixMn2O4, LixV2O5, or LixV3O8. The first two classes of materials built on close-packed oxygen stacking adopt bidimensional and tridimensional crystal structures, respectively (Figure 1), from which lithium ions may be easily intercalated or extracted in a reversible manner. These oxides are reasonably good ionic and electronic conductors, and lithium insertion/extraction proceeds while operating on the M4+/M3+ redox couple, located between 4 and 5 V versus Li+/Li...

Polyanionic (phosphates, silicates, sulfates) frameworks as electrode materials for rechargeable Li (or Na) batteries.

Most minerals of Earth's upper mantle contain small amounts of hydrogen, structurally bound as hydroxyl (OH). The OH concentration in each mineral species is variable, in some cases reflecting the geological environment of mineral formation. Of the major mantle minerals, pyroxenes are the most hydrous, typically containing ∼200 to 500 parts per million H_2O by weight, and probably dominate the water budget and hydrogen geochemistry of mantle rocks that do not contain a hydrous phase. Garnets and olivines commonly contain ∼1 to 50 parts per million. Nominally anhydrous minerals constitute a significant reservoir for mantle hydrogen, possibly accommodating all water in the depleted mantle and providing a possible mechanism to recycle water from Earth's surface into the deep mantle.

https://science.sciencemag.org/content/sci/255/5050/1391.full.pdf

Water in Earth's Mantle: The Role of Nominally Anhydrous Minerals

We review recent results concerning the rheology of the lithosphere with special attention to the following topics: 1) the flexure of the oceanic lithosphere, 2) deformation of the continental lithosphere resulting from vertical surface loads and forces applied at plate margins, 3) the rheological stratification of the continents, 4) strain localization and shear zone development, and 5) strain-induced crystallographic preferred orientations and anisotropies in body-wave velocities. We conclude with a section citing the 1983–1986 rock mechanics literature by category.

Rheology of the lithosphere: Selected topics

To investigate the kinetics of diffusion of hydrogen in olivine, single crystals from San Carlos in Arizona have been annealed at temperatures between 800° and 1000°C under hydrothermal conditions at a confining pressure of 300 MPa. The hydrogen diffusivities were determined for the [100], [010], and [001] directions from concentration profiles for hydroxyl in the samples. These profiles were obtained from infrared spectra taken at 100-μm intervals across a thin slice which was cut from the central portion of each annealed crystal. The rate of diffusion is anisotropic, with fastest transport along the [100] axis and slowest along the [010] axis. The fit of the data to an Arrhenius law for diffusion parallel to [100] yields an activation enthalpy of 130±30 kJ/mol with a preexponential term of (6±3)×10−5 m2 s−1. For diffusion parallel to [001], as there are insufficient data to calculate the activation enthalpy for diffusion, we used the same value as that for diffusion parallel to [100] and determined a preexponential term of (5±4)×10−6 m2 s−1. The diffusion rate parallel to [010] is about 1 order of magnitude slower than along [001]. The measured diffusivities are large enough that the hydrogen content of olivine grains which are millimeters in diameter will adjust to changing environmental conditions in time scales of hours at temperatures as low as 800°C. As xenoliths ascending from the mantle remain at high temperatures (i.e., >1000°C) but experience a rapid decrease in pressure, and hence hydrogen fugacity, olivine grains may dehydrate during ascent. By comparison, slow rates of carbon diffusion (Tingle et al., 1988) suggest that carbon will not be lost from olivine during ascent. Thus, low hydrogen contents within olivine and within fluid inclusions in olivine cannot be taken as support for low water contents in the mantle.

Diffusion of hydrogen in olivine: Implications for water in the mantle

To calibrate infrared (IR) spectroscopy for quantitative analysis of trace structural OH in specific minerals, we have determined concentrations of H in pure separates of mantle derived pyrope garnet (56 ± 6 ppm H_2O by weight), augite (268 ± 8, ppm H_2O, and enstatite (217 ± 11 ppm H_2O) by manometry after heating the samples and extracting H_2 gas under vacuum. IR spectroscopy confirmed the presence of intrinsic OH in these samples prior to extraction and indicated between 86 and 100% removal of H during the extraction procedure. The integral specific absorption coefficients of 1.39 ± 0.14(lσ),7.09
± 0.32, and 15.6 ± 0.94 /(ppm H_2O.cm^2) for pyrope, augite, and enstatite, respectively, allow precise spectroscopic determination of the OH content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million. Uncertainties in accuracy depend on mineral composition and characteristics of the OH absorption spectrum and are estimated to range between ± 10 and ± 50%.

http://minsocam.org/msa/ammin/toc/articles_free/1995/bell_p465-474_95.pdf

Quantitative analysis of trace OH in garnet and pyroxenes

Olivine, (Mg, Fe)_2SiO_4, is the predominant mineral in the upper mantle and a study of its defect structure is fundamental to an understanding of the rheological laws that describe mantle flow. Existing models are based on creep mechanisms in which point and line defects have a major role. Here we report the first observations, by transmission electron microscopy (TEM), of planar defects in olivine. The displacement vector associated with the defects, R = 1/4 , together with infrared absorption spectra suggest that the structure of the defects resembles that of an OH-bearing monolayer within the olivine, as exists in the humite family of minerals. Because the planar defects were formed in the upper mantle, their discovery has important implications for the deformation of olivine at high pressures and temperatures in the presence of trace quantities of water, as well as revealing another possible reservoir of water in the upper mantle.

Planar OH-bearing defects in mantle olivine

Synthetic laihunite ( x Fe (super 2+) (sub 2-3x) Fe (super 3+) 2x SiO 4 ), an oxidation product of olivine

Laihunite, a nonstoichiometric distorted olivine-type mineral, has been studied by X-ray diffraction, electron-probe microanalysis, and analytical electron microscopy. Our results indicate that the laihunite is actually a mixture of laihunite and magnetite and has been derived by oxidation of fayalite. A pseudo-twin relation among the fine domains of laihunite also supports the transformation of fayalite to laihunite. The apparent composition of laihunite material obtained by rrun and AEM is that of a mixture of laihunite and magnetite. The true composition of laihunite is nonstoichiometric, but close to a stoichiometric Fe2 + Fe3r* Si2O6.

Fine textures of laihunite, a nonstoichiometric distorted olivine-type mineral

La Sous-Commission Pyroxenes creee par la Commission Nouveaux Mineraux et Noms de Mineraux (C.N.M.M.N.) de l'Association Mineralogique Internationale (I.M.A.) presente son rapport final sur la nomenclature des pyroxenes. Les recommandations de la Sous-Commission proposees dans ce rapport ont ete officiellement acceptees par la Commission. Des noms acceptes et largement utilises ont ete definis chimiquement, combinant des methodes nouvelles et conventionnelles, de facon a etre en accord dans la mesure du possible avec l'usage actuel generalement admis. Vingt noms ont ete officiellement acceptes, parmi eux treize sont employes pour representer des poles purs de composition chimique bien determinee. Dans les solutions solides binaires ordinaires, les noms d'especes sont donnes par les termes extremes suivant la "regle des 50%". Des adjectifs modificatifs sont ajoutes aux noms des pyroxenes pour indiquer des quantites exceptionnelles de constituants chimiques. Ce rapport inclut une liste de 105 noms de pyroxene utilises precedemment, qui ont ete rejetes officiellement par la Commission.

Nobuo Morimoto

Papers

Planar OH-bearing defects in mantle olivine

Synthetic laihunite ( x Fe (super 2+) (sub 2-3x) Fe (super 3+) 2x SiO 4 ), an oxidation product of olivine

Fine textures of laihunite, a nonstoichiometric distorted olivine-type mineral

Nomenclature of pyroxenes

A transmission electron microscope study of pyroxene chondrules in equilibrated L-group chondrites