Ming FANG
,
Qinghui LI
,
Fuxi GAN
材料科学技术（英）
The optical absorption properties of phase-change optical recording thin films subjected to various initialization conditions were investigated. The effects of initialization power and velocity on optical constants of the Ge2Sb2Te5 thin films were also studied. The energy gap of Ge2Sb2Te5 thin films subjected to various initialization conditions was also obtained. It was found that the optical energy gap of the Ge2Sb2Te5 thin films increased with either increasing initialization laser power or decreasing initialization velocity, with peak of 0.908 eV at laser power of 1000 mW or initialization velocity of 4.0 m/s, but the continued increasing initialization laser power or decreasing initialization velocity resulted in the decrease of the optical energy gap. The change of the optical energy gap was discussed on the basis of amorphous crystalline transformation.
关键词:
Phase transformation
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Journal of Physics-Condensed Matter
The electronic structure of TiB2 has been calculated using the self-consistent LMTO-ASA method. Our results have been compared with experimental and other theoretical work. We find that the pseudo-gap at the Fermi level is the competing effect of Ti 3d resonance and strong hybridization between Ti 3d and B 2p states. The bonding nature of TiB2 is discussed. We have carried out calculations of the equation of state (EOS) Of TiB2; it is found that our first-principles calculated results support the universal model of EOS proposed by Vinet et al. The room-temperature isotherm is also plotted.
关键词:
binding-energy relation;borides;solids;chemisorption;metals
Journal of Physics and Chemistry of Solids
The ground state splitting of d(5) configuration ion Mn2+ in ZnS:Mn2+ has been studied by diagonalizing the energy matrices for electron-electron repulsion, spin-orbit coupling and trigonal ligand field interactions. It is shown that in order to give a unified explanation for the EPR parameters a, D and (a - F) for Mn2+ in ZnS:Mn2+, a positive Dq has to be employed. This means that in tetrahedral ZnS the sulfur ion has a positive effective charge. This unusual result supports the Pauling's speculation that the sulfur ion in ZnS may be looked upon as an electron donor that forms a quadricovalent argon state of S2+ with sp(3) hybrid configuration. (C) 2003 Elsevier Ltd. All rights reserved.
关键词:
electron paramagnetic resonance;site symmetry;ion;zns;spectra;sulfide
Journal of Magnetism and Magnetic Materials
The ground-state magnetic properties of the spin-2 transverse Ising model with a longitudinal crystal field are studied within the framework of mean-field theory (MFT) and effective-field theory (EFT), respectively. The phase diagrams and magnetization curves are examined in detail. It is found that the system exhibits a tricritical behavior in the ground-state phase diagrams. Some interesting phenomena have been found, especially the first-order phase transition from one ordered phase to the other ordered phase, which is due to the high spin. The spin correlation has important effect on the magnetic properties of the system. We also find that the ground-state phase diagrams of the spin-2 transverse Ising model are very different from those of the spin-3/2 transverse Ising model. (C) 2007 Elsevier B.V. All rights reserved.
关键词:
spin-2 transverse ising model;mean-field theory;effective-field;theory;first-order phase transition;crystal-field;phase
Condensed Matter Physics
The (63)Cu Knight shifts and g factors for the normal state of YBa(2)Cu(3)O(7) in tetragonal phase are theoretically studied in a uniform way from the high (fourth-) order perturbation formulas of these parameters for a 3d(9) ion under tetragonally elongated octahedra. The calculations are quantitatively correlated with the local structure of the Cu(2+) (2) site in YBa(2)Cu(3)O(7). The theoretical results show good agreement with the observed values, and the improvements are achieved by adopting fewer adjustable parameters as compared to the previous works. It is found that the significant anisotropy of the Knight shifts is mainly attributed to the anisotropy of the g factors due to the orbital interactions.
关键词:
electron paramagnetic resonance;nuclear magnetic resonance;Knight;Shift;(63)CU;YBa(2)Cu(3)O(7)
Journal of Magnetism and Magnetic Materials
The ground-state phase diagrams and the magnetization curves of the spin-3/2 transverse Ising model with longitudinal crystal field D are studied within the framework of mean-field theory (MFT) and effective-field theory (EFT), respectively. A simple calculation method of the internal energy is presented within the framework of EFT. In the ground-state phase diagram given by using EFT, the second-order phase transition line is divided into two segments by the first-order phase transition line: one starts from a critical end point and extends to D -> -infinity; the other one starts from a tricritical point and extends to D -> +infinity, while it does not occur in MFT. Some interesting phenomena of the first-order phase transition from one ordered phase to another one ordered have been found. (c) 2007 Elsevier B.V. All rights reserved.
关键词:
spin-3/2 transverse Ising model;mean-field theory;effective-field;theory;first-order phase transition;crystal-field;phase-transitions
