| 1. |
- Zeng, Qiao-Shi, et al.
(författare)
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Substitutional alloy of Ce and Al
- 2009
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 106:8, s. 2515-2518
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Tidskriftsartikel (refereegranskat)abstract
- The formation of substitutional alloys has been restricted to elements with similar atomic radii and electronegativity. Using high-pressure at 298 K, we synthesized a face-centered cubic disordered alloy of highly dissimilar elements (large Ce and small Al atoms) by compressing the Ce3Al intermetallic compound > 15 GPa or the Ce3Al metallic glass > 25 GPa. Synchrotron X-ray diffraction, Ce L-3-edge absorption spectroscopy, and ab initio calculations revealed that the pressure-induced Kondo volume collapse and 4f electron delocalization of Ce reduced the differences between Ce and Al and brought them within the Hume-Rothery (HR) limit for substitutional alloying. The alloy remained after complete release of pressure, which was also accompanied by the transformation of Ce back to its ambient 4f electron localized state and reversal of the Kondo volume collapse, resulting in a non-HR alloy at ambient conditions.
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| 2. |
- Aamodt, K., et al.
(författare)
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The ALICE experiment at the CERN LHC
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3:S08002
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Forskningsöversikt (refereegranskat)abstract
- ALICE (A Large Ion Collider Experiment) is a general-purpose, heavy-ion detector at the CERN LHC which focuses on QCD, the strong-interaction sector of the Standard Model. It is designed to address the physics of strongly interacting matter and the quark-gluon plasma at extreme values of energy density and temperature in nucleus-nucleus collisions. Besides running with Pb ions, the physics programme includes collisions with lighter ions, lower energy running and dedicated proton-nucleus runs. ALICE will also take data with proton beams at the top LHC energy to collect reference data for the heavy-ion programme and to address several QCD topics for which ALICE is complementary to the other LHC detectors. The ALICE detector has been built by a collaboration including currently over 1000 physicists and engineers from 105 Institutes in 30 countries, Its overall dimensions are 16 x 16 x 26 m(3) with a total weight of approximately 10 000 t. The experiment consists of 18 different detector systems each with its own specific technology choice and design constraints, driven both by the physics requirements and the experimental conditions expected at LHC. The most stringent design constraint is to cope with the extreme particle multiplicity anticipated in central Pb-Pb collisions. The different subsystems were optimized to provide high-momentum resolution as well as excellent Particle Identification (PID) over a broad range in momentum, up to the highest multiplicities predicted for LHC. This will allow for comprehensive studies of hadrons, electrons, muons, and photons produced in the collision of heavy nuclei. Most detector systems are scheduled to be installed and ready for data taking by mid-2008 when the LHC is scheduled to start operation, with the exception of parts of the Photon Spectrometer (PHOS), Transition Radiation Detector (TRD) and Electro Magnetic Calorimeter (EMCal). These detectors will be completed for the high-luminosity ion run expected in 2010. This paper describes in detail the detector components as installed for the first data taking in the summer of 2008.
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| 3. |
- Ding, Yang, et al.
(författare)
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Structural phase transition of vanadium at 69 GPa
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:8
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Tidskriftsartikel (refereegranskat)abstract
- A phase transition was observed at 63-69 GPa and room temperature in vanadium with synchrotron x-ray diffraction. The transition is characterized as a rhombohedral lattice distortion of the body-centered-cubic vanadium without a discontinuity in the pressure-volume data, thus representing a novel type of transition that has never been observed in elements. Instead of driven by the conventional s-d electronic transition mechanism, the phase transition could be associated with the softening of C-44 trigonal elasticity tensor that originates from the combination of Fermi surface nesting, band Jahn-Teller distortion, and electronic topological transition.
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| 4. |
- Luo, Wei, et al.
(författare)
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Unusual lattice dynamics of vanadium under high pressure
- 2007
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 104:42, s. 16428-16431
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structures and lattice dynamics of pressure-induced complex phase transitions [bcc -> hRl(110.5 degrees) -> distorted-hRl(108.2') -> bcc] in vanadium as a function of pressure up to 400 GPa have been investigated with an ab initio method using density functional perturbation theory (DFPT). At ambient pressure, the soft transverse acoustic phonon mode corresponding to Kohn anomaly appears at a wave vector q = 2k(F) along [xi 00] Gamma -> H high symmetry direction. The nonclegenerate transverse acoustic branches TA(1) on < 110 > and TA(2) on < 001 > show an exceptionally large split at high symmetry point N (0.5 0.5 0.0). The lattice dynamical instability starts at a pressure of 62 GPa (V/V-0 = 0.78, where V-0 is experimental volume of bcc-V at ambient conditions), derived by phonon softening that results in phase transition of bcc -> hR1 (alpha = 110.5 degrees). At compression around 130 GPa (V/V-0 = 0.67), the rhombohedral angle of hR1 phase changed to 108.2 degrees, and the electronic structure changed drastically. At even higher pressure, approximate to 250 GPa (V/V-0 = 0.57), lattice dynamic calculations show that the bcc structure becomes stable again.
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