Search results for "Absorption"
showing 10 items of 2701 documents
Electronic structure of CuAlO2 and CuScO2 delafossites under pressure
2007
The electronic structure of CuAlO 2 and CuScO 2 delafossites is investigated by means of optical absorption measurements under pressure and ab initio band structure calculations. Measurements are carried out on CuAlO 2 monocrystals and pulsed laser deposited CuAlO 2 and CuScO 2 thin films up to 20 GPa. CuAlO 2 is an indirect semiconductor that is stable in the pressure range explored here. The pressure coefficients of the indirect and direct gaps are found to be 15 meV/GPa and 2 meV/GPa respectively. CuScO 2 is a direct semiconductor and the pressure coefficient of the excitonic peak energy is -5.5 meV/GPa. Two reversible phase transitions are observed in CuScO 2 . At 13 GPa the delafossite…
Photophysical Properties of Discotic Dibenzopyrenes
1997
Abstract The photophysical properties of three discogenic dibenzopyrenes substituted by eight pentyloxy (O5DPB), heptyloxy (O7DBPP) or decyloxy (O10DBP) side chains are studied in solution and thin films. It is shown that the absorption and fluorescence spectra of the columnar mesophases are clearly distinguishable from those of the corresponding crystalline phases, allowing the study of phase transitions. Thus, it is found that the shorter the lateral chain length, the slower the crystallisation process. For O5DBP, the supercooled mesophase is stable over a period of at least one year; it crystallises after cooling below the glassy transition. Such a behaviour gives rise to temperature con…
Structure Solution of the High-Pressure Phase of CuWO4 and Evolution of the Jahn–Teller Distortion
2011
In this work, we have investigated the structural behavior of cuproscheelite up to 33.9 GPa by means of high-pressure single-crystal X-ray diffraction (SXRD) and extended X-ray absorption fine structure (EXAFS). According to EXAFS, beyond 9 GPa a phase transition takes place. On the basis of SXRD, the transition is from the triclinic (P1) structure to a monoclinic (P2/c) structure isotypic to wolframite. The transition implies abrupt changes of CuO6 and WO6 octahedra, but no coordination change. Further, we report the role played by the Jahn–Teller distortion of the CuO6 octahedra on the mechanism of the phase transition as well as the changes in the behavior of the Cu–O bonds for the tricl…
High pressure–high temperature phase diagram of InSe
2004
By combining X-ray diffraction and X-ray absorption spectroscopy, the structural evolution of the InSe alloy has been explored up to 3.3 GPa and 1500 K with the use of the Paris–Edinburgh large volume cell. These conditions allowed us to study the solid and the liquid states and to measure the pressure evolution of the melting point, which increases at a rate of +120 K GPa−1. A temperature‐induced phase transition has been evidenced within the solid phase. This is the first in-situ study of the high temperature solid phase which had so far only been inferred from studies on recovered samples at ambient conditions.
Cation Environment of BaCeO3−Based Protonic Conductors II: New Computational Models
2011
Quantum chemical calculations have been carried out to simulate Y-doped BaCeO(3) derivatives. Hartree-Fock energy functional was used to study octahedral site environments embedded in a Pmcn orthorhombic framework, showing local arrangement characterized by Ce-O-Ce, Ce-O-Y, and Y-O-Y (Z-O-Ξ) configurations and including or not hydrogen close to the moieties encompassing those configurations. The latter are, in fact, representative of - and, in our modeling approach, were treated as - local arrangements that could be found in Y:BaCeO(3)-doped materials. The geometrical optimizations performed on the structural models and a detailed orbital analysis of these systems allowed us to confirm and …
ChemInform Abstract: Chemistry and Properties of Solids with the (NZP) Skeleton
2010
Abstract Solids with an [NZP] skeleton in their structure from a very broad family presenting very different properties with varying chemical composition. These properties range from radioactive nuclide immobilization and insulation to ionic and/or electronic conduction, extending to the field of very low thermal expansion among others. The open [NZP] skeleton provides the stability and flexibility necessary to form continuous ranges of solid solution, allowing the tailoring of the best composition-property-structure material. Chemical activity may become particularly high at the surface and absorption reactions and catalytic properties have the highest interest at present. In this paper, c…
Attosecond state-resolved carrier motion in quantum materials probed by soft x-ray XANES
2021
Recent developments in attosecond technology led to tabletop X-ray spectroscopy in the soft X-ray range, thus uniting the element- and state-specificity of core-level x-ray absorption spectroscopy with the time resolution to follow electronic dynamics in real time. We describe recent work in attosecond technology and investigations into materials such as Si, SiO2, GaN, Al2O3, Ti, TiO2, enabled by the convergence of these two capabilities. We showcase the state-of-the-art on isolated attosecond soft x-ray pulses for x-ray absorption near edge spectroscopy (XANES) to observe the 3d-state dynamics of the semi-metal TiS2 with attosecond resolution at the Ti L-edge (460 eV). We describe how the …
Phase transition of tetragonal copper sulfide Cu2S at low temperatures
2017
The low-temperature behavior of tetragonal copper sulfide, ${\mathrm{Cu}}_{2}\mathrm{S}$, was investigated by powder and single-crystal x-ray diffraction, calorimetry, electrical resistance measurements, and ambient temperature optical absorption spectroscopy. The experiments were complemented by density-functional-theory-based calculations. High-quality, polycrystalline samples and single crystals of tetragonal copper sulfide were synthesized at 5 GPa and 700 K in a large volume multianvil press. Tetragonal ${\mathrm{Cu}}_{2}\mathrm{S}$ undergoes a temperature-induced phase transition to an orthorhombic structure at around 202 K with a hysteresis of $\ifmmode\pm\else\textpm\fi{}21$ K, an e…
Recent progress in high pressure X-ray absorption spectroscopy studies at the ODE beamline
2020
I.J. and A.K. are grateful to the Latvian Council of Science project no. lzp-2018/2-0353 for financial support. The research leading to these results has been partially supported by the project CALIPSOplus under the Grant Agreement No. 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.
Temperature Dependence of Electronic Transitions of Single-Wall Carbon Nanotubes: Observation of an Abrupt Blueshift in Near-Infrared Absorption
2007
Near-infrared (NIR) absorption spectra of single-wall carbon nanotube (SWNT) films are studied between 10 and 293 K. The most prominent effect is the shift of bands with temperature. Some nanotubes show a redshift of transition upon increasing temperature while some show blueshift and others show no shift. The shift is interpreted to originate mainly from the effect of strain induced in the tubes because of interaction with the environment. In particular, at temperatures T = 175−225 K, for some bands, there is an abrupt large blueshift, which is interpreted to originate from interaction of the nanotubes with water. Two models could be considered to explain the effect: (1) strain induced by…