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| 2. |
- Belonoshko, Anatoly B., et al.
(författare)
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High-pressure crystal structure studies of Fe, Ru and Os
- 2004
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Ingår i: Journal of Physics and Chemistry of Solids. - : Elsevier BV. - 0022-3697 .- 1879-2553. ; 65:09-aug, s. 1565-1571
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Tidskriftsartikel (refereegranskat)abstract
- In order to reveal structural trends with increasing pressure in d transition metals, we performed full potential linear muffin-tin orbital calculations for Fe, Ru, and Os in the hexagonal close packed structure. The calculations cover a wide volume range and demonstrate that all these hexagonal close-packed metals have non-ideal c/a at low pressures which, however, increases with pressure and asymptotically approaches the ideal value at very high compressions. These results are in accordance with most recent experiment for Ru and Os. The experimental data for iron is not conclusive, but it is believed that the c/a ratio decreases weakly with increasing pressure at moderate compression. Since, the experimental and calculated equations of state for iron are in increasingly good agreement with increasing pressure, it is possible that either the negative c/a trend is valid only for a restricted pressure range, or related to the experimental difficulties (e.g. non-hydrostaticity).
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| 3. |
- Heathman, S., et al.
(författare)
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The unique high-pressure behavior of curiurn probed further using alloys
- 2007
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 444, s. 138-141
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Tidskriftsartikel (refereegranskat)abstract
- The changing role of the 5f electrons across the actinide series has been of prime interest for many years. The remarkable behavior of americium's 5f electrons under pressure was determined experimentally a few years ago and it precipitated a strong interest in the heavy element community. Theoretical treatments of americium's behavior under pressure followed and continue today. Experimental and theoretical findings regarding curium's behavior under pressure have shown that the pressure behavior of curium was not a mirror image of that for americium. Rather, one of the five crystallographic phases observed with curium (versus four for americium) was a unique monoclinic structure whose existence is due to a spin stabilization effect by curium's 5f(7) electronic configuration and its half-filled 5f-shell. We review briefly the behavior of pure curium under pressure but focus on the pressure behaviors of three curium alloys with the intent of comparing them with pure curium. An important experimental finding confirmed by theoretical computations, is that dilution of curium with its near neighbors is sufficient to prevent the formation of the unique C2/c phase that appears in pure Cm metal under pressure. As this unique C2/c phase is very sensitive to having a 5f7 configuration to maximize the magnetic spin polarization, dilution of this state with adjacent actinide neighbors reduces its stability.
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| 4. |
- Hu, Q. M., et al.
(författare)
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Phase stability and elastic modulus of Ti alloys containing Nb, Zr, and/or Sn from first-principles calculations
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:12
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Tidskriftsartikel (refereegranskat)abstract
- The alloying effects of Nb, Zr, and/or Sn on the phase stability and elastic properties of Ti are investigated by using a first-principles method. Our calculation results indicate that a carefully designed Ti-Nb-Zr-Sn system can be a good candidate for low modulus biomedical materials. We find that the well-known correlation between the e/a ratio and both elastic and phase stabilities for Ti alloyed with transition metal elements breaks down for the Ti-Sn alloy.
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| 5. |
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| 6. |
- Li, S., et al.
(författare)
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Crystallographic structures of PbWO4
- 2003
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Ingår i: High Pressure Research. - : Informa UK Limited. - 0895-7959 .- 1477-2299. ; 23:3, s. 343-347
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Li, S., et al.
(författare)
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Optical properties of Ti3SiC2 and Ti4AlN3
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:22
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Tidskriftsartikel (refereegranskat)abstract
- The dielectric functions of the MAX phases, Ti3SiC2 and Ti4AlN3, have been determined from first principles calculations. We compared the dielectric functions and the reflectivity spectra of Ti3SiC2 and Ti4AlN3 with those of TiC and TiN. The optical spectra were analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of these two phases. We found that Ti4AlN3 can be used to avoid solar heating and also increase the radiative cooling due to the increased thermal emittance as compared to TiN. Ti4AlN3 can therefore be a candidate coating material for temperature control of space vehicles.
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| 8. |
- Dewhurst, J. K., et al.
(författare)
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Lattice dynamics of solid xenon under pressure
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 88:7
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Tidskriftsartikel (refereegranskat)abstract
- We use density-functional perturbation theory to obtain the phonon spectrum of fcc xenon under pressure. Thermodynamic properties obtained within the quasiharmonic approximation are in fair to good agreement with experiment at zero pressure. The transition pressure from the fcc to hcp phase is predicted to occur at 5 GPa. The fcc structure is found to be dynamically stable up to a pressure of 100 GPa, beyond which the phonon modes at the X and L symmetry points soften. We attribute the observed sluggish kinetics of the fcc-hcp transition to the small energy difference between the phases as well as to the high dynamical stability of the fcc phase.
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| 9. |
- Heathman, S., et al.
(författare)
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A high-pressure structure in curium linked to magnetism
- 2005
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 309:5731, s. 110-113
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Tidskriftsartikel (refereegranskat)abstract
- Curium ties at the center of the actinide series and has a half-filled shell. with seven 5f electrons spatially residing inside its radon core. As a function of pressure, curium exhibits five different crystallographic phases up to 100 gigapascals, of which all but one are also found in the preceding element, americium. We describe here a structure in curium, Cm III, with monoctinic symmetry, space group C2/c, found at intermediate pressures (between 37 and 56 gigapascals). Ab initio electronic structure calculations agree with the observed sequence of structures and establish that it is the spin polarization of curium's 5f electrons that stabilizes Cm Ill. The results reveal that curium is one of a few elements that has a lattice structure stabilized by magnetism.
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| 10. |
- Holm, B., et al.
(författare)
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Theory of the ternary layered system Ti-Al-N
- 2002
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:12, s. 9874-9877
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Tidskriftsartikel (refereegranskat)abstract
- We present calculations on the physical properties of Ti4AlN3 obtained from first principles, as well as some general observations concerning this group of materials. We further report mechanical data obtained through numerical simulations for some representative phases, and elaborate on the issue of high pressure stability. By examining the density of states of Ti4AlN3, we conclude that it is a semimetal, and we predict an opening up of the band gap around the Fermi level with increasing pressure.
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