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Development of an Experimental Platform for Combinative Use of an XFEL and a High-Power Nanosecond Laser
摘要： We developed an experimental platform for combinative use of an X-ray free electron laser (XFEL) and a high-power nanosecond laser. The main target of the platform is an investigation of matter under high-pressure states produced by a laser-shock compression. In this paper, we show details of the experimental platform, including XFEL parameters and the focusing optics, the laser irradiation system and X-ray diagnostics. As a demonstration of the high-power laser-pump XFEL-probe experiment, we performed an X-ray di?raction measurement. An in-situ single-shot X-ray di?raction pattern expands to a large angle side, which shows a corundum was compressed by laser irradiation.
关键词： X-ray di?raction,high-pressure science,laser shock,XFEL
更新于2025-09-23 15:21:01
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Unexpected robustness of the band gaps of TiO <sub/>2</sub> under high pressures
摘要： Titanium dioxide (TiO2) is a wide band gap semiconducting material which is promising for photocatalysis. Here we present first-principles calculations to study the pressure dependence of structural and electronic properties of two TiO2 phases: the cotunnite-type and the Fe2P-type structure. The band gaps are calculated using density functional theory with the generalized gradient approximation, as well as the many-body perturbation theory with the GW approximation. The band gaps of both phases are found to be unexpectedly robust across a broad range pressures. The corresponding pressure coefficients are significantly smaller than that of diamond and silicon carbide, whose pressure coefficient is the smallest value ever measured by experiment. The robustness originates from the synchronous change of valence band maximum and conduction band minimum with nearly identical rates of changes. A step-like jump of band gaps around the phase transition pressure point is expected and understood in light of the difference in crystal structures.
关键词： band gap,robustness,TiO2,first-principles calculations,high pressure
更新于2025-09-23 15:21:01
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Coexistence of pressure-induced structural phases in bulk black phosphorus: a combined x-ray diffraction and Raman study up to 18 GPa
摘要： We report a study of the structural phase transitions induced by pressure in bulk black phosphorus by using both synchrotron x-ray diffraction for pressures up to 12.2 GPa and Raman spectroscopy up to 18.2 GPa. Very recently black phosphorus attracted large attention because of the unique properties of few-layers samples (phosphorene), but some basic questions are still open in the case of the bulk system. As concerning the presence of a Raman spectrum above 10 GPa, which should not be observed in an elemental simple cubic system, we propose a new explanation by attributing a key role to the non-hydrostatic conditions occurring in Raman experiments. Finally, a combined analysis of Raman and XRD data allowed us to obtain quantitative information on presence and extent of coexistences between different structural phases from ~5 up to ~15 GPa. This information can have an important role in theoretical studies on pressure-induced structural and electronic phase transitions in black phosphorus.
关键词： high pressure,black phosphorus,x-ray diffraction,Raman spectroscopy,phase transitions
更新于2025-09-23 15:21:01
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Pressure-Driven Reversible Switching between <i>n</i> - and <i>p</i> -Type Conduction in Chalcopyrite CuFeS <sub/>2</sub>
摘要： Temperature-dependent switching between p- and n-type conduction is a newly observed phenomenon in very a few Ag-based semiconductors, which may promote fascinating applications in modern electronics. Pressure, as an efficient external stimulus that has driven collective phenomena such as spin crossover and Mott transition is also expected to initialize a conduction type switching in transition metal based semiconductors. Herein, we report the observation of a pressure-driven dramatic switching between p- and n-type conduction in chalcopyrite CuFeS2 associated with a structural phase transition. Under compression around 8 GPa, CuFeS2 undergoes a phase transition with symmetry breakdown from space group I-42d to I-4 accompanying with a remarkable volume shrinkage of the FeS4 tetrahedra. A high-to-low spin-crossover of Fe2+ (S = 2 to S = 0) is manifested along with this phase transition. Instead of pressure-driven metallization, a surprising semiconductor-to-semiconductor transition is observed associated with the structural and electronic transformations. Significantly, both photocurrent and Hall coefficient measurements confirm that CuFeS2 undergoes a reversible pressure-driven p-n type conduction switching accompanying with the structural phase transition. The absence of cationic charge transfer between copper and iron during the phase transition is confirmed by both X-ray absorption near-edge spectra (Cu/Fe, K-edge) and total-fluorescence-yield X-ray absorption spectra (Fe, K-edge) results, and the valence distribution maintains Cu2+Fe2+S2 in the high pressure phase. The observation of an abrupt pressure-driven p-n type conduction switching in a transition metal based semiconductor paves the way to novel pressure-responsive switching devices.
关键词： High pressure,Magnetic semiconductor,CuFeS2,p-n switching,Spin-crossover
更新于2025-09-23 15:21:01
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Synthesis of Na <i> <sub/>x</sub></i> MoO <sub/>3</sub> crystals through high pressure solid-state reaction
摘要： We report growth of high-purity single crystals of the sodium molybdenum bronzes NaxMoO3 through high pressure solid-state reaction routes. Our results demonstrate that the crystallite sizes of NaxMoO3 can rapidly grow to ～25 μm under a moderate pressure of 4.0 GPa in just 10 min. This discovery provides a starting point for the growth of large single crystals of alkali metal molybdenum bronzes under high pressure.
关键词： High pressure,molybdenum bronze,reaction
更新于2025-09-23 15:21:01
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Structural and thermodynamic properties of cubic sphalerite aluminum nitride under hydrostatic compression
摘要： The present work aims to investigate the structural phase stability and thermodynamic properties of aluminium nitride with cubic zinc-blende structure at normal and high pressures (up to 5 GPa) and high temperatures (up to 2000 K). In this study, we use the pseudopotential plane wave method within the framework of the density functional theory with the local density approximation for the exchange-correlation functional. The phase transition pressure has been determined and found to be in very good agreement with several theoretical data. The pressure and temperature dependences of thermodynamic properties are successfully presented, analyzed and discussed in details. Besides, the plasmon energy and microhardness are examined.
关键词： High-pressure,Ab-initio calculation,High-temperature,Thermodynamic properties,Aluminium nitride
更新于2025-09-23 15:19:57
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Temperature measurement in double-sided laser-heated diamond anvil cell and reaction of carbon
摘要： In this work, a double-sided laser-heated diamond anvil cell facility for studies at extreme conditions of pressure and temperature that has been developed is described in detail. Phase transitions occurring at extreme conditions can be mapped by accurate measurements of pressure and temperature. Micrometer-sized diamond crystals having regular facets have been synthesized at a pressure of 18 GPa and temperature 1785 K, which is con?rmed by visual inspection, micro-Raman and ?eld emission scanning electron micrograph measurements. A low-temperature gradient is observed across the sample surface during the formation of micrometer-sized diamond crystals. Our observation restricts the use of steel gasket as it can react with carbon (C) transported from the diamond anvil. The reaction of C with one of the potential thermal insulating medium Al2O3 is observed in the X-ray diffraction measurements.
关键词： Laser-heated diamond anvil cell,High pressure,Reaction of carbon
更新于2025-09-23 15:19:57
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Pushing Boundaries: High Pressure, Supercritical Optical Floating Zone Materials Discovery
摘要： In this perspective review, we provide the rationale for utilizing supercritical fluids for solid state materials discovery in the context of recent advances in the field of high pressure synthesis. We discuss the importance of the transition from gas-like to solvent-like environments in which materials synthesis and crystallization is occurring, the appropriate conceptual frameworks for its impact on synthesis and directional solidification, and dispel popular myths. We provide an overview of materials that have been grown in single crystal form by the high pressure optical floating zone technique, report the first successful stable molten zone in an optical furnace at P = 300 bar, and show viability of the traveling solvent method even with high fluid pressures. Further, we report on some unexpected observations found in the highly dynamic synthesis environment of supercritical fluids, enabled by the ability to observe, in real time, materials behavior. Finally, we offer a perspective on the scientific domains opened by these new capabilities.
关键词： Single crystal growth,Materials discovery,Optical floating zone,High pressure synthesis,Supercritical fluids
更新于2025-09-23 15:19:57
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Synthesis of organic–inorganic hybrids <i>via</i> a high-pressure-ramp process: the effect of inorganic nanoparticle loading on structural and photochromic properties
摘要： Organic polymerization remains a limiting step in the preparation of organic–inorganic hybrid materials with a strong concentration of the inorganic component. In this work, a high-pressure-ramp process was applied to achieve pHEMA–TiO2 nanoparticulate solids with an unprecedentedly high concentration (12 mol l?1) of the inorganic component, which is four times higher than that obtained after radical polymerization induced thermally or by photons. The inorganic nanoparticles underwent morphological and structural changes with an increase of Ti concentration above 1.5 mol l?1: they slightly coarsen and crystallize into an anatase polymorph. The material possesses a strong photochromic response related to the electron–hole separation at the organic–inorganic interface and can store 1e? per 5 Ti atoms. The electron storage capacity of the titania nanoparticles decreases upon crystallization.
关键词： high-pressure-ramp process,polymerization,TiO2 nanoparticles,photochromic properties,organic–inorganic hybrids
更新于2025-09-19 17:15:36
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[IEEE 2018 Seventh Balkan Conference on Lighting (BalkanLight) - Varna (2018.9.20-2018.9.22)] 2018 Seventh Balkan Conference on Lighting (BalkanLight) - Particularities of photometric calculation and non-sinusoidal operation regime of luminaires with high pressure sodium vapour lamps
摘要： In the first part of this paper, the authors present an analysis from photometrical (technical lighting) point of view of a DELFIN 03 type luminaire used in the modern street lighting. For this it started from determining by calculation (using a numerical calculation method - the method of equal plane angles) of the total luminous flux emitted by the street luminaire (polar photometric curves are required - polar luminous intensity distribution in different planes) and of the efficiency. The distribution of illuminances to different montage heights was then analyzed. In the second part of the paper, is presented a comparative study of the harmonic (distorted) regime produced by these luminaires equipped with high pressure sodium vapour tubular lamps type HST E40 socket, 250 W, for a network of street public lighting. In this regard was used an own conception computation program, developed in the Mathcad programming environment completed with an Excel subprogram.
关键词： harmonic analysis,photometric calculation,luminaires,high pressure sodium vapour lamps,non-sinusoidal operation regime
更新于2025-09-19 17:15:36