Search results for "Ambient pressure"
showing 10 items of 40 documents
Spin crossover behaviour in the iron(II)-2,2-dipyridilamine system: Synthesis, X-ray structure and magnetic studies
2005
Abstract The monomeric compounds [Fe(dpa)2(X)2] · solv [X = NCS−(solv = 0.5H2O) (1), N ( CN ) 2 - (2) and dpa = 2,2-dipyridilamine] have been synthesised and characterised. They crystallise in the P21/n and in the Cc monoclinic systems, respectively. Four of six nitrogen atoms coordinated to the Fe(II) ions belong to two dpa ligands which lie in cis conformation. The remaining positions are occupied by two nitrogen atoms of the pseudo-halide ligands. The magnetic susceptibility measurements at ambient pressure have revealed that compound 1 exhibits an incomplete spin crossover behaviour (T1/2 ≈ 88 K), whereas compound 2 remains in the high-spin configuration. Pressure studies performed on c…
Equilibrium properties of the reaction H2⇌ 2H by classical molecular dynamics simulations
2013
We have developed a classical molecular dynamics model for the hydrogen dissociation reaction, containing two- and three-particle potentials derived by Kohen, Tully and Stillinger. Two fluid densities were investigated for a wide range of temperatures, and 11 fluid densities were considered for one temperature. We report the temperature range where the degree of reaction is significant, and also where a stable molecule dominates the population in the energy landscape. The three-particle potential, which is essential for the reaction model and seldom studied, together with the two-particle interaction lead to a large effective excluded volume diameter of the molecules in the molecular fluid.…
Equation of state and high-pressure/high-temperature phase diagram of magnesium
2014
The phase diagram of magnesium has been investigated to 211 GPa at 300 K, and to 105 GPa at 4500 K, by using a combination of x-ray diffraction and resistive and laser heating. The ambient pressure hcp structure is found to start transforming to the bcc structure at ∼45 GPa, with a large region of phase-coexistence that becomes smaller at higher temperatures. The bcc phase is stable to the highest pressures reached. The hcp-bcc phase boundary has been studied on both compression and decompression, and its slope is found to be negative and steeper than calculations have previously predicted. The laser-heating studies extend the melting curve of magnesium to 105 GPa and suggest that, at the h…
High-pressure theoretical and experimental study of HgWO4
2011
HgWO 4 at ambient pressure is characterized using a combination of ab initio calculations, X-ray diffraction and Raman scattering measurements. The effect of low pressure and temperature on the structural stability is analysed. Extending our ab initio study to the range of higher pressures, a sequence of stable phases up to 30GPa is proposed. © 2011 Taylor & Francis.
Pressure-restored superconductivity in Cu-substituted FeSe
2011
Copper doping of FeSe destroys its superconductivity at ambient pressure, even at low doping levels. Here we report the pressure-dependent transport and structural properties of Fe${}_{1.01\ensuremath{-}x}$Cu${}_{x}$Se with 3$%$ and 4$%$ Cu doping and find that the superconductivity is restored. Metallic resistivity behavior, absent in Cu-doped FeSe, is also restored. At the low pressure of 1.5 GPa, superconductivity is seen at 6 K for 4$%$ Cu doping, somewhat lower than the 8 K ${T}_{c}$ of undoped FeSe. ${T}_{c}$ reaches its maximum of 31.3 K at 7.8 GPa, lower than the maximum superconducting temperature in the undoped material under pressure (${T}_{c}$ max of 37 K) but still very high. X…
Trapping of three-dimensional electrons and transition to two-dimensional transport in the three-dimensional topological insulator Bi2Se3under high p…
2012
This paper reports an experimental and theoretical investigation on the electronic structure of bismuth selenide (Bi2Se3) up to 9 GPa. The optical gap of Bi2Se3 increases from 0.17 eV at ambient pressure to 0.45 eV at 8 GPa. The quenching of the Burstein-Moss effect in degenerate samples and the shift of the free-carrier plasma frequency to lower energies reveal a quick decrease of the bulk three-dimensional (3D) electron concentration under pressure. On increasing pressure the behavior of Hall electron concentration and mobility depends on the sample thickness, consistently with a gradual transition from mainly 3D transport at ambient pressure to mainly two-dimensional (2D) transport at hi…
Synthesis of Graphene Nanoribbons by Ambient-Pressure Chemical Vapor Deposition and Device Integration
2016
Graphene nanoribbons (GNRs), quasi-one-dimensional graphene strips, have shown great potential for nanoscale electronics, optoelectronics, and photonics. Atomically precise GNRs can be "bottom-up" synthesized by surface-assisted assembly of molecular building blocks under ultra-high-vacuum conditions. However, large-scale and efficient synthesis of such GNRs at low cost remains a significant challenge. Here we report an efficient "bottom-up" chemical vapor deposition (CVD) process for inexpensive and high-throughput growth of structurally defined GNRs with varying structures under ambient-pressure conditions. The high quality of our CVD-grown GNRs is validated by a combination of different …
Pressure Effect Studies on the Spin‐Transition Behavior of a Dinuclear Iron(II) Compound
2013
Magnetic studies into the effect of different hydrostatic pressures between ambient and 1.03 GPa on the high-spin (HS) i low-spin (LS) transition behavior of the dinuclear iron(II) compound [Fe II 2(PMAT)2](BF4)4·DMF (1, PMAT = 4-amino3,5-bis{[(2-pyridylmethyl)amino]methyl}-4H-1,2,4-triazole, DMF = N,N-dimethylformamide) have been carried out at 2– 300 K. Under ambient pressure, the sample studied exhibits a [HS–HS] to [HS–LS] half spin transition (ST) at T½ = 208 K without any thermal hysteresis. Increasing the pressure above 0.2 GPa causes an increase (initially rapid but above 0.5 GPa more gradual) of T½ as well as a matching reduction in the residual high-spin fraction at room temperatu…
Synergy of Miniemulsion and Solvothermal Conditions for the Low-Temperature Crystallization of Magnetic Nanostructured Transition-Metal Ferrites
2017
Crystalline first-row transition-metal (Mn, Fe, Co, Ni, Cu, and Zn) ferrites were prepared by an unprecedented synergetic combination of miniemulsion synthesis and solvothermal route, pursuing unconventional conditions in terms of space confinement, temperature, and pressure. This synergy allowed for obtaining six different crystalline ferrites at much lower temperature (i.e., 80 °C) than usually required and without any postsynthesis thermal treatment. X-ray diffraction (XRD) revealed that analogous ferrites synthesized by miniemulsion at ambient pressure or in bulk (i.e., from an aqueous bulk solution and not in the confined space of the miniemulsion droplets) either at ambient pressure o…
Pressure Dependence of the Bandgap Bowing in Zinc-Blende ZnTe 1− x Se x
2002
We report on the pressure dependence of the bandgap bowing in the ZnTe 1 m x Se x alloy, in the whole composition range. The bandgap bowing parameter is shown to increase almost linearly with pressure from 1.23 at ambient pressure to 1.6 at 7 GPa. Saturation effects observed in the pressure dependence for x =0.1 and x =0.2 are shown to be related to the direct-to-indirect crossover. Results are discussed and interpreted in the framework of structural relaxation models for gap bowing. A prediction of these models (the negative bowing of the o 15 m ;X 1 transition) is shown to be compatible with the fact that the direct-to-indirect crossover pressure increases with the Se content.