Compressibility of solid c60

Room-temperature powder x-ray diffraction profiles have been obtained at hydrostatic pressures P = 0 and 1.2 gigapascals on the solid phase of cubic C(60) ("fullerite"). Within experimental error, the linear compressibility d(ln a)/dP is the same as the interlayer compressibility d(ln c)/dP of hexagonal graphite, consistent with van der Waals intermolecular bonding. The volume compressibility -d(ln V)/dP is 7.0 +/- 1 x 10(-12) square centimeter per dyne, 3 and 40 times the values for graphite and diamond, respectively.     

High-Pressure Polymorph of Thulium: An X-ray Diffraction Study

An x-ray diffractiotn study of thulium at room temperature and high pressure by means of a diamond-anvil press has shown that thulium transforms from a hexagonal close-packed structure to the samarium type, as other rareearth elements (gadolinium, terbium, dysprosium, and holmium) do. Unlike the other rare-earth elements, thulium (hexagonal close-packed) has an axial ratio (c/a) that is independent of pressure within experimental error and the transition is reversible. The transition occurs with increasing pressure in the range of 60 to 116 kilobars. The lattice paralieters of the samarium-type phase of thulium at about 116 kilobars are a = 3.327 +/- 0.005 angstroms and c = 23.48 +/- 0.04 angstroms, and the volume change at the transition is estimated to be - 0.5 percent of the volume of the hexagonal close-packed phase at the transition.     

Doping graphitic and carbon nanotube structures with boron and nitrogen

Composite sheets and nanotubes of different morphologies containing carbon, boron, and nitrogen were grown in the electric arc discharge between graphite cathodes and amorphous boron-filled graphite anodes in a nitrogen atmosphere. Concentration profiles derived from electron energy-loss line spectra show that boron and nitrogen are correlated in a one-to-one ratio; core energy-loss fine structures reveal small differences compared to pure hexagonal boron nitride. Boron and carbon are anticorrelated, suggesting the substitution of boron and nitrogen into the carbon network. Results indicate that singlephaase CyBxNx as well as separated domains (nanosize) of boron nitride in carbon networks may exist.     

Modified phases of diamond formed under shock compression and rapid quenching

Two modified forms of carbon were quenched by a rapid-cooling technique from graphite sheets shock-compressed to 65 gigapascals and 3700 K. One form, ;;n-diamond," which was obtained from the most rapidly cooled part, has a crystal structure close to that of cubic diamond. The other form, found in the relatively slow-cooled part, was comparable to an i-carbon prepared by an ion-beam technique. The n-diamond is interpreted as a metastable form, the same as hexagonal diamond, converted from graphite through a martensitic transition, for which either the region or the path may be different from that of hexagonal diamond. The second form was found to be produced through reconstruction.     

Hexagonal diamonds in meteorites: implications

A new polymorph of carbon, hexagonal diamond, has been discovered in the Canyon Diablo and Goalpara meteorites. This phase had been synthesized recently under specific high-pressure conditions in the laboratory. Our results: provide strong evidence that diamonds found in these meteorites were produced by intense shock pressures acting on crystalline graphite inclusions present within the meteorite before impact, rather than by disintegration of larger, statically grown diamonds, as some theories propose.     

Phosphide from metorites: barringerite, a new iron-nickel mineral

Schreibersite, (Fe,Ni)(3)P, and a higher phosphide, barringerite, occur in the Ollague pallasite. The composition of the higher phosphide, determined by electron probe microanalysis, is (Fe(0.58)Ni(0.42)Co(0.003))(1.95)P. It is hexagonal, with space group P62m and a = 5.87 +/- 0.07 angstroms and c = 3.44 +/- 0.04 angstroms. If we assume a primary origin, the new mineral indicates that troilite and schreibersite crystallized at high temperatures. The occurrence of a higher phosphide in a pallasite indicates local nonequilibria within a group of meteorites that are remarkable for their overall degree of equilibrium crystallization.     

Application of carbon isotope stratigraphy to late miocene shallow marine sediments, new zealand

A distinct (0.5 per mil) carbon-13/carbon-12 isotopic shift in the light direction has been identified in a shallow marine sedimentary sequence of Late Miocene age at Blind River, New Zealand, and correlated with a similar shift in Late Miocene Deep Sea Drilling Project sequences throughout the Indo-Pacific. A dated piston core provides an age for the shift of 6.2 +/- 0.1 million years. Correlations based on the carbon isotopic change require a revision of the previously established magnetostratigraphy at Blind River. The carbon shift at Blind River occurs between 6.2 and 6.3 +/- 0.1 million years before present. A new chronology provides an age for the evolutionary first appearance datum of Globorotalia conomiozea at 6.1 +/- 0.1 million years, the beginning of a distinct latest Miocene cooling event associated with the Kapitean stage at 6.2 +/- 0.1 million years, and the beginning of a distinct shallowing of water depths at 6.1 +/- 0.1 million years. The Miocene-Pliocene boundary as recognized in New Zealand is now dated at 5.3 +/- 0.1 million years. Extension of carbon isotope stratigraphy to other shallow Late Miocene sequences should provide an important datum for international correlation of Late Miocene shallow and deep marine sequences.     

Crystal Structure of the Solid Electrolyte(C5H5NH) Ag5I6 at -30{degrees}C

The crystal structure of pyridinium hexaiodopentaargentate, (C(5)H(5)NH) Ag(5)l(6), is unique among those of the halide and chalcogenide solid electrolytes in that face-sharing iodide octahedra as well as face-sharing tetrahedra and face-sharing between octahedra and tetrahedra provide the paths for silver ion transport. There are two formula units in a hexagonal cell, space group P6/mcc (D6h(2)). At -30 degrees C, the lattice constants are a = 11.97 +/- 0.02, c = 7.41 +/- 0.01 A. The structure has three sets of sites for the silver ions. At -30 degrees C two of these sets are apparently filled with the ten silver ions per unit cell, while the third set of tetrahedrally coordinated general positions is empty. Therefore, the conductivity at this temperature is limited by the thermal excitation of the silver ions into the empty tetrahedra.     

Lead: X-ray Diffraction Study of a High-Pressure Polymorph

An x-ray diffraction study of lead under pressure has shown that face-centered cubic structure transforms to the hexagonal close-packed structure at room temperature and a pressure of 130+/- 10 kilobars. The volume change for the transformation is -0.18+/- 0.06 cubic centimeter per mole.     

Degradation of terrigenous dissolved organic carbon in the western Arctic Ocean

The largest flux of terrigenous organic carbon into the ocean occurs in dissolved form by way of rivers. The fate of this material is enigmatic; there are numerous reports of conservative behavior over continental shelves, but the only knowledge we have about removal is that it occurs on long unknown time scales in the deep ocean. To investigate the removal process, we evaluated terrigenous dissolved organic carbon concentration gradients in the Beaufort Gyre of the western Arctic Ocean, which allowed us to observe the carbon's slow degradation. Using isotopic tracers of water-mass age, we determined that terrigenous dissolved organic carbon is mineralized with a half-life of 7.1 +/- 3.0 years, thus allowing only 21 to 32% of it to be exported to the North Atlantic Ocean.     

A large terrestrial carbon sink in north america implied by atmospheric and oceanic carbon dioxide data and models

Atmospheric carbon dioxide increased at a rate of 2.8 petagrams of carbon per year (Pg C year-1) during 1988 to 1992 (1 Pg = 10(15) grams). Given estimates of fossil carbon dioxide emissions, and net oceanic uptake, this implies a global terrestrial uptake of 1.0 to 2. 2 Pg C year-1. The spatial distribution of the terrestrial carbon dioxide uptake is estimated by means of the observed spatial patterns of the greatly increased atmospheric carbon dioxide data set available from 1988 onward, together with two atmospheric transport models, two estimates of the sea-air flux, and an estimate of the spatial distribution of fossil carbon dioxide emissions. North America is the best constrained continent, with a mean uptake of 1.7 +/- 0.5 Pg C year-1, mostly south of 51 degrees north. Eurasia-North Africa is relatively weakly constrained, with a mean uptake of 0.1 +/- 0.6 Pg C year-1. The rest of the world's land surface is poorly constrained, with a mean source of 0.2 +/- 0.9 Pg C year-1.     

Carbynes in meteorites: detection, low-temperature origin, and implications for interstellar molecules

Carbon from the Allende meteorite is not graphite but carbyne (triply bonded elemental carbon), inasmuch as on heating to 250 degrees to 330 degrees C it releases mainly triply bonded fragments: -(C identical withC)(n),- with n = 1 to 5, and -(C identical withC)(n)-CN, with n = 1 to 3. Although carbynes have been known to form only by condensation of carbon vapor above 2600 K or by explosive shock of > 600 kilobars, it is found that they also form metastably by the reaction 2CO --> CO(2) + C (solid) at 300 degrees to 400 degrees C in the presence of a chromite catalyst. Such low-temperature formation by surface catalysis may be the dominant source of carbynes on the earth and in meteorites, and a major source of interstellar carbynes and cyanopolyacetylenes.     

低碳球铁及其性能

低碳球铁是一种介于钢与铸铁之间的新材料,经过由某些公认的球化及反球化元素共同组成的SX变质剂变质处理以后,石墨以细小圆整的球状析出。对于这种新材料的性能、组织特点进行了实验研究。发现这种新型铸铁具有较高的抗拉强度与冲击韧性,可以作为耐磨材料来使用。     

采用变温X射线衍射技术对六方钛酸钡陶瓷材料的结构监控

对于由冷压陶瓷技术所开发的纯六方Ba（Ti0.95Fe0.05）O3-δ陶瓷，采用变温XRD技术测量该陶瓷在不同温度下的XRD谱，鉴定晶体结构．澄清了六方钛酸钡（BaTiO3）介电陶瓷材料的晶体结构是否在BaTiO3的居里温度（n=130℃）发生结构相变，并验证开发的变温X射线衍射（XRD）技术在无机粉体材料结构监控的可行性．结果表明：BaTiO3陶瓷在Tc发生四方-立方的结构相变，以45°附近两个分立的（002）／（200）衍射峰演变为单一对称的（200）衍射峰为标志；而六方Ba（Ti0.95Fe0.05）O3-δ陶瓷直到300℃都不发生结构相变．对于六方Ba（Ti0.95Fe0.05）O3-δ陶瓷，升高温度并不能导致吸附环境氧来填充氧空位，Fe3＋Vo-Fe3＋缺陷复合体所维持的晶格电中性仍占据统治地位，六方-立方结构相变不发生．该项研究为变温XRD技术在工业生产上对无机粉体材料的监控应用提供了技术依据．     

A Fluorite Isotype of SnO2 and a New Modification of TiO2: Implications for the Earth's Lower Mantle

The existence of a cubic fluorite-type SnO(2) and a hexagonal TiO(2) (which may be related to the fluorite structure) have been demonstrated by an in situ x-ray diffraction study in which a diamond-anvil pressure cell was used after the samples had been heated by a continuous yttrium-aluminum-garnet laser. At room temperature, the lattice parameter for SnO(2) (fluorite) is a = 4.925 +/- 0.005 angstroms and those for TiO(2) (fluorite-related) are a = 9.22 +/- 0.01 angstroms and c = 5.685 +/- 0.006 angstroms at about 250 kilobars. The volume change associated with the transition from rutile to fluorite (or related structure) is about -8 percent for SnO(2) and -10.5 percent for TiO(2) at transition. Upon release of pressure, both the fluorite-type SnO(2) and the TiO(2) reverted to the alpha-PbO(2) structure at room temperature. The hypothesis that the earth's lower mantle is composed of oxide phases might be feasible if it were possible for SiO(2) to possess the fluorite structure or its related forms at high pressure, as shown for SnO(2) and TiO(2) in this study. The oxide hypothesis proposed here differs from that postulated by Birch in that the primary coordination of silicon is 6 for Birch's hypothesis and 8 for the hypothesis presented here.     

Interannual variability in the North Atlantic Ocean carbon sink

The North Atlantic is believed to represent the largest ocean sink for atmospheric carbon dioxide in the Northern Hemisphere, yet little is known about its temporal variability. We report an 18-year time series of upper-ocean inorganic carbon observations from the northwestern subtropical North Atlantic near Bermuda that indicates substantial variability in this sink. We deduce that the carbon variability at this site is largely driven by variations in winter mixed-layer depths and by sea surface temperature anomalies. Because these variations tend to occur in a basinwide coordinated pattern associated with the North Atlantic Oscillation, it is plausible that the entire North Atlantic Ocean may vary in concert, resulting in a variability of the strength of the North Atlantic carbon sink of about +/-0.3 petagrams of carbon per year (1 petagram = 10(15) grams) or nearly +/-50%. This extrapolation is supported by basin-wide estimates from atmospheric carbon dioxide inversions.     

Hexagonal pattern in cell walls of Escherichia coli B

Cell walls, isolated from Escherichia coli B, as examined by electron microscopy and optical diffraction contain a hexagonal lattice structure, the (1,0) planes of which are separated by 140 +/- 8 angstroms. Unless the walls are briefly heated (10 minutes, 90 degrees C) early in the isolation, the hexagonal array cannot always be observed. Enzymatic digestion with pancreatin and amylase improves visualization of the lattice; subsequent treatment with pepsin and sodium dodecylsulfate removes the hexagonal pattern. Protein or lipoprotein globular units within the wall may thus be arranged in a hexagonal array uponthe mucopeptide layer.     

Bonding changes in compressed superhard graphite

Compressed under ambient temperature, graphite undergoes a transition at approximately 17 gigapascals. The near K-edge spectroscopy of carbon using synchrotron x-ray inelastic scattering reveals that half of the pi-bonds between graphite layers convert to sigma-bonds, whereas the other half remain as pi-bonds in the high-pressure form. The x-ray diffraction pattern of the high-pressure form is consistent with a distorted graphite structure in which bridging carbon atoms between graphite layers pair and form sigma-bonds, whereas the nonbridging carbon atoms remain unpaired with pi-bonds. The high-pressure form is superhard, capable of indenting cubic-diamond single crystals.     

Phase transformations in carbon fullerenes at high shock pressures

C(60) powders were shock-compressed quasi-isentropically and quenched from pressures in the range 10 to 110 GPa (0.1 to 1.1 Mbar). Recovered specimens were analyzed by Raman spectroscopy and optical microscopy. C(60) fullerenes are stable into the 13- to 17-GPa pressure range. The onset of a fast ( approximately 0.5 micros) reconstructive transformation to graphite occurs near 17 GPa. The graphite recovered from 27 GPa and about 600 degrees C is relatively well ordered with crystal planar domain size of about 100 A. Above 50 GPa a continuous transformation to an amorphous state is observed in recovered specimens. The fast transformation to graphite is proposed to occur by pi-electron rehybridization which initiates breakup of the ball structure and formation of the graphite structure at high density.     

X-ray Diffraction to 302 Gigapascals: High-Pressure Crystal Structure of Cesium Iodide

X-ray diffraction measurements have been carried out on cesium iodide (CsI) to 302 gigapascals with a platinum pressure standard. The results indicate that above 200 gigapascals CsI at 300 K has a hexagonal close-packed crystal structure with the ideal c/a ratio of 1.63 +/- 0.01. The crystal structure and pressure-volume relations converge at high pressure with those of solid xenon, which is isoelectronic with CsI. The results indicate a significant loss of ionic bonding in the hexagonal close-packed metallic phase of CsI at ultrahigh pressure.