The high-pressure metallization and electrical transport behaviors of GaSb were systematically investigated using in situ temperature-dependent electrical resistivity measurements, Hall effect ...measurements, transmission electron microscopy analysis, and first-principles calculations. The temperature-dependent resistivity measurements revealed pressure-induced metallization of GaSb at approximately 7.0 GPa, which corresponds to a structural phase transition from F-43m to Imma. In addition, the activation energies for the conductivity and Hall effect measurements indicated that GaSb undergoes a carrier-type inversion (p-type to n-type) at approximately 4.5 GPa before metallization. The first-principles calculations also revealed that GaSb undergoes a phase transition from F-43m to Imma at 7.0 GPa and explained the carrier-type inversion at approximately 4.5 GPa. Finally, transmission electron microscopy analysis revealed the effect of the interface on the electrical transport behavior of a small-resistance GaSb sample and explained the discontinuous change of resistivity after metallization. Under high pressure, GaSb undergoes grain refinement, the number of interfaces increases, and carrier transport becomes more difficult, increasing the electrical resistivity.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A novel class of polymers and oligomers of chiral folding chirality has been designed and synthesized, showing structurally compacted triple-column/multiple-layer frameworks. Both uniformed and ...differentiated aromatic chromophoric units were successfully constructed between naphthyl piers of this framework. Screening monomers, catalysts, and catalytic systems led to the success of asymmetric catalytic Suzuki-Miyaura polycouplings. Enantio- and diastereochemistry were unambiguously determined by X-ray structural analysis and concurrently by comparison with a similar asymmetric induction by the same catalyst in the asymmetric synthesis of a chiral three-layered product. The resulting chiral polymers exhibit intense fluorescence activity in a solid form and solution under specific wavelength irradiation.
The high-pressure behavior of molybdenum disulfide (MoS
2) has been investigated using an energy dispersive synchrotron X-ray diffraction method in a diamond anvil cell to 38.8
GPa at room ...temperature. It is found that the
c-axis compression ratio is about three times larger than
a-axis at pressures below 10
GPa. It gradually decreases with increasing pressure, and reduces to two times above 28.9
GPa. The reduction of
c-axis with pressure displayed a discontinuity between 20.5 and 28.9
GPa. This may result from a phase transformation. The experimental pressure–volume data below 20.5
GPa were fitted with the third-order Birch–Murnaghan equation of state, and the bulk modulus was obtained as
K
0T=53.4±1
GPa and its pressure derivative as
K′
0T=9.2±0.4.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The phase diagram of water near the ice VI-ice VII-liquid triple point and electrical transport properties of these ices have been studied by
in situ
electrical conductivity measurements in a diamond ...anvil cell. The obtained phase boundary between ices VI and VII and the melting curve for these ices are in accord with most previous results. The different properties and amount of orientational defects in ice VI and ice VII are associated with abrupt changes in conductivity when a phase transition from ice VI to ice VII occurs. The electrical transport mechanisms of these two ice polymorphs can be understood in terms of the conduction of the already existing ions and Bjerrum defects.
The phase boundary between ices VI and VII and melting curves for these ices were determined by measuring electrical conductivity with a diamond anvil cell.
The subduction of oceanic lithosphere into the Earth's deep interior is thought to drive convection and create chemical heterogeneity in the mantle. The oceanic lithosphere as a whole, however, might ...not subduct uniformly: the fate of basaltic crust may differ from that of the underlying peridotite layer because of differences in chemistry, density and melting temperature. It has been suggested that subducted basaltic crust may in fact become buoyant at the mantle's 660-km discontinuity, remaining buoyant to depths of at least 800 km, and therefore might be gravitationally trapped at this boundary to form a garnetite layer, . Here we report the phase relations and melting temperatures of natural mid-ocean ridge basalt at pressures up to 64 GPa (corresponding to ∼1,500 km depth). We find that the former basaltic crust is no longer buoyant when it transforms to a perovskitite lithology at about 720 km depth, and that this transition boundary has a positive pressure-temperature slope, in contrast to the negative slope of the transition boundary in peridotite. We therefore predict that basaltic crust with perovskitite lithology would gravitationally sink into the deep mantle. Our melting data suggest that, at the base of the lower mantle, the former basaltic crust would be partially molten if temperatures there were to exceed 4,000 K.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The high-pressure, high-temperature behavior of iron has been investigated to 161
GPa and 3000
K by in situ synchrotron X-ray diffraction with double-side laser-heated diamond anvil cells. We found ...that only α-, γ- and ε-Fe can be clearly verified as the stable solid phase in the
P–
T range studied. Only ε-Fe is observed from deep lower mantle (∼1500
km) to outer core conditions. Within the
P–
T range examined, we did not observe a significant change with pressure or temperature on the
c/
a ratio of ε-Fe. The melting curve of iron has been determined to 105
GPa. A Lindeman law fit gives a melting point of iron at the inner core boundary of 5800 (±200)
K, which provides an upper bound on the temperature at that depth. We also examine numerous experimental factors that may complicate the analysis of high
P–
T diffraction data, and discuss the effects of sample stress on the X-ray diffraction results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A high pressure angle dispersive synchrotron x-ray diffraction study of titanium disulfide (TiS(2)) was carried out to pressures of 45.5 GPa in a diamond-anvil cell. We observed a phase ...transformation of TiS(2) beginning at about 20.7 GPa. The structure of the high pressure phase needs further identification. By fitting the pressure-volume data to the third-order Birch-Murnaghan equation of state, the bulk modulus, K(0T), was determined to be 45.9 ± 0.7 GPa with its pressure derivative, K'(0T), being 9.5 ± 0.3 at pressures lower than 17.8 GPa. It was found that the compression behavior of TiS(2) is anisotropic along the different axes. The compression ratio of the c-axis is about nine times larger than the a-axis when pressures are lower than 1 GPa. It suddenly decreases to three times larger at pressures of about 3 GPa. This ratio shows a linear decrease with a slope of negative 0.048 at pressures below phase transformation.
An alternate current impedance spectrum was utilized to differentiate the electrical transport process, respectively, in the bulk and the grain boundary of barium tungstate microcrystallines under ...high pressures up to 20 GPa. For powdered BaWO4 microcrystallines, the grain boundary makes a more remarkable contribution than the bulk to the total resistance. The discontinuities of bulk resistance and relaxation frequency at about 7 and 14 GPa reflect the pressure-induced structural phase transitions of BaWO4 from scheelite to fergusonite structure and from fergusonite to an unknown disordered structure, respectively. The activation energy of the grain boundary decreases with increasing pressure from 6.9 to 8.9 GPa, indicating that the compression has a negative contribution to the activation energy and the transport of charge carriers through the boundary becomes easier. The activation energy of the bulk also shows a similar phenomenon. In addition, the ascending relaxation frequency of the bulk and grain boundary shows that the polarization process needs much shorter time in the state of three-phase coexistence.
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