Eu doped γ-La2S3 were synthesized by the sulfurization of their oxide powders using CS2 gas at 700 ℃. During the sulfurizing reaction process, the cubic Eu3S4 crystals of prior formation acted as the nuclei sites of...Eu doped γ-La2S3 were synthesized by the sulfurization of their oxide powders using CS2 gas at 700 ℃. During the sulfurizing reaction process, the cubic Eu3S4 crystals of prior formation acted as the nuclei sites of the γ-La2S3 phase to facilitate the nucleation process. The γ-La2S3 transformation occurred at significantly lower temperature by the combined contributions of low transformation enthalpy and induced multiple nuclei. On the other hand, the doped Eu ions could be inserted into the empty tetrahedral S4 cavities to stabilize the γ-La2S3 phase at temperature excess of 1100 ℃.展开更多
The band structures,density of states,phonon,optical properties,and thermodynamic properties of β-La_2S_3 were calculated from first-principles using the plane-wave pseudopotential method.First,the structures were fu...The band structures,density of states,phonon,optical properties,and thermodynamic properties of β-La_2S_3 were calculated from first-principles using the plane-wave pseudopotential method.First,the structures were fully relaxed through the first-principles method.Then,the zone-center phonon-mode frequencies were evaluated within the framework of density functional perturbation theory.Properties related to the structure,phonons,optics,elastic constants,and thermodynamics of β-La_2S_3 were reported.The dielectric function,refractive index,absorption coefficient,extinction coefficient,infrared（IR） reflectance,energy,heat capacity,and Debye temperature spectra were also given β-La_2S_3 was a direct-gap semiconductor,and calculation indicated that its energy gap was 0.191 eV.From the phonon spectra,it could be concluded that the lattice dynamics were stable.A strong IR reflection occurred in a range of 0-1000 nm,arising from several strong IR-active modes,resulting in poor transmission properties.Relatively good transmission properties were observed in the range above 2000 nm,with low reflectivity and dissipation due to the absence of IR-active or weak modes.展开更多
The as-sintered sinter skin and the polished section of WC-11Co-0.4Cr 3 C 2-0.3VC-0.2RE（RE=mischmetal with La/Ce ratio of 0.65） alloy were analyzed.It was shown that the microstructures on the skin and in the inner ...The as-sintered sinter skin and the polished section of WC-11Co-0.4Cr 3 C 2-0.3VC-0.2RE（RE=mischmetal with La/Ce ratio of 0.65） alloy were analyzed.It was shown that the microstructures on the skin and in the inner part of the alloy were all characterized with a WC＋β＋M structure,where β was a cobalt-based binder phase and M represented a RE-containing phase.There existed an inward diffusion of S atoms,which caught and fixed the Ce atoms in the alloy and an outward diffusion of La atoms during the sintering process.Consequently,the M phase was characterized with the decreased La/Ce ratio（0.59） in the inner part and the increased La/Ce ratio（1.01） on the skin.The M phase on the skin was characterized with a γ-Ce 2 S 3 type structure.To suppress the long range migration of rare earth to the skin,S in the sintering atmosphere had to be eliminated.展开更多
基金supported by New Century Educational Talents Plan of Chinese Education Ministry, China (NCET-10-0171)the National Natural Sci-ence Foundation of China (60979003)the Fundamental Research Funds for the Central Universities (2009QN123)
文摘Eu doped γ-La2S3 were synthesized by the sulfurization of their oxide powders using CS2 gas at 700 ℃. During the sulfurizing reaction process, the cubic Eu3S4 crystals of prior formation acted as the nuclei sites of the γ-La2S3 phase to facilitate the nucleation process. The γ-La2S3 transformation occurred at significantly lower temperature by the combined contributions of low transformation enthalpy and induced multiple nuclei. On the other hand, the doped Eu ions could be inserted into the empty tetrahedral S4 cavities to stabilize the γ-La2S3 phase at temperature excess of 1100 ℃.
基金supported by National Natural Science Foundation of China(51372203,51332004,51571166,11304238)
文摘The band structures,density of states,phonon,optical properties,and thermodynamic properties of β-La_2S_3 were calculated from first-principles using the plane-wave pseudopotential method.First,the structures were fully relaxed through the first-principles method.Then,the zone-center phonon-mode frequencies were evaluated within the framework of density functional perturbation theory.Properties related to the structure,phonons,optics,elastic constants,and thermodynamics of β-La_2S_3 were reported.The dielectric function,refractive index,absorption coefficient,extinction coefficient,infrared（IR） reflectance,energy,heat capacity,and Debye temperature spectra were also given β-La_2S_3 was a direct-gap semiconductor,and calculation indicated that its energy gap was 0.191 eV.From the phonon spectra,it could be concluded that the lattice dynamics were stable.A strong IR reflection occurred in a range of 0-1000 nm,arising from several strong IR-active modes,resulting in poor transmission properties.Relatively good transmission properties were observed in the range above 2000 nm,with low reflectivity and dissipation due to the absence of IR-active or weak modes.
基金supported by National Natural Science Foundation of China (51074189,50823006)Science and Technology Planning Project Founda-tion of Hunan Province,China (2010FJ2006)+1 种基金Research Foundation for the Doctoral Program of Higher Education of China (20100162110001)the National Science & Technology Special Foundation of China (2011BAE09B02,2012ZX04003021)
文摘The as-sintered sinter skin and the polished section of WC-11Co-0.4Cr 3 C 2-0.3VC-0.2RE（RE=mischmetal with La/Ce ratio of 0.65） alloy were analyzed.It was shown that the microstructures on the skin and in the inner part of the alloy were all characterized with a WC＋β＋M structure,where β was a cobalt-based binder phase and M represented a RE-containing phase.There existed an inward diffusion of S atoms,which caught and fixed the Ce atoms in the alloy and an outward diffusion of La atoms during the sintering process.Consequently,the M phase was characterized with the decreased La/Ce ratio（0.59） in the inner part and the increased La/Ce ratio（1.01） on the skin.The M phase on the skin was characterized with a γ-Ce 2 S 3 type structure.To suppress the long range migration of rare earth to the skin,S in the sintering atmosphere had to be eliminated.
