Based on the first-principle calculations for 3D Hofmann-like spin-crossover （SCO） compound [Fe（C4H4N2）{Pt（CN）4}], the discrepancy of transition mechanism is clarified with quantitatively distinguishable evidenc...Based on the first-principle calculations for 3D Hofmann-like spin-crossover （SCO） compound [Fe（C4H4N2）{Pt（CN）4}], the discrepancy of transition mechanism is clarified with quantitatively distinguishable evidence of second order phase transition. It shows that the stretch around 0.2 ？ of Fe-N bond length leads to the continuous structure expansion, as the energy splitting ΔEHL between low-spin and high-spin states reduces from 2.554 2 eV to -0.327 8 eV, and the crystal-field splitting （CFS） is reduced from 1.845 8 eV to 0.420 8 eV meanwhile. A physics image relating the calculations results with CFS in the frame of ligand-field theory is presented, which manifests that CFS is a necessary parameter to be introduced directly in the theory of spin-state transition.展开更多
Any electronic eigenstate of the paramagnetic ion open-shell is characterized by the three independent multipole asphericities for and 6 related to the second moments of the relevant crystal-field splittings by , wher...Any electronic eigenstate of the paramagnetic ion open-shell is characterized by the three independent multipole asphericities for and 6 related to the second moments of the relevant crystal-field splittings by , where . The Ak as the reduced matrix elements can serve as a reliable measure of the state capability for the splitting produced by the k-rank component of the crystal-field Hamiltonian. These multipolar characteristics allow one to verify any fitted crystal-field parameter set by comparing the calculated second moments and the experimental ones of the relevant crystal-field splittings. We present the multipole characteristics Ak for the extensive set of eigenstates from the lower parts of energy spectra of the tripositive 4 f N ions applying in the calculations the improved eigenfunctions of the free lanthanide ions obtained based on the M. Reid f-shell programs. Such amended asphericities are compared with those achieved for the simplified Russell-Saunders states. Next, they are classified with respect to the absolute or relative weight of Ak in the multipole structure of the considered states. For the majority of the analyzed states (about 80%) the Ak variation is of order of only a few percent. Some essential changes are found primarily for several states of Tm3+, Er3+, Nd3+, and Pr3+ ions. The detailed mechanisms of such Ak changes are unveiled. Particularly, certain noteworthy cancelations as well as enhancements of their magnitudes are explained.展开更多
Complexes Cl-RuⅡ（dppe）2（Fe Cl4）·2CH2Cl2（2） and Br-RuII（dppe）2（Fe Br4）·2CH2Cl2（3） were prepared by the reaction of trans-RuII（dppe）2Cl2（1） with FeX 3（X = Cl, Br）. More interestingly, the ce...Complexes Cl-RuⅡ（dppe）2（Fe Cl4）·2CH2Cl2（2） and Br-RuII（dppe）2（Fe Br4）·2CH2Cl2（3） were prepared by the reaction of trans-RuII（dppe）2Cl2（1） with FeX 3（X = Cl, Br）. More interestingly, the central Ru atoms of RuII（dppe）-based complexes（2 and 3） define a tetragonal pyramid with five-coordination. The temperature dependence magnetic susceptibilities indicate that the xMT values of complexes 2 and 3 are almost constant at 50~300 K, and the xMT values sharply decrease with further decreasing the temperature at low temperature due to the zero-field splitting（ZFS） of high spin Fe（III） ions.展开更多
The electron-phonon(el-ph)and phonon-phonon interactions play a key role in determining electronic and thermal transport properties,respectively,in promising two-dimensional(2D)semiconductor de-vices.In this study,we ...The electron-phonon(el-ph)and phonon-phonon interactions play a key role in determining electronic and thermal transport properties,respectively,in promising two-dimensional(2D)semiconductor de-vices.In this study,we investigated el-ph interactions using Wannier-Fourier interpolation method and renormalized phonon scattering considering finite-temperature effects in Bi_(2)TeSe_(2)monolayer.The re-sults show that the optical phonon modes dominate the carrier scattering,where level repulsion induced by crystal field splitting and spin-orbit coupling(SOC)effect effectively suppresses intervalley scattering,leading to high hole mobility.Moreover,the strong anharmonicity in Bi_(2)TeSe_(2)monolayer results in the temperature-dependent softening of its optical phonons,along with a corresponding variation in interatomic force constants(IFCs).As a result,the lattice thermal conductivity is remarkably low and exhibits weak temperature dependence.Finally,the predicted dimensionless thermoelectric figure of merit exceeds unity in the range of 200-800 K,indicating the potential of Bi_(2)TeSe_(2)monolayer for thermoelectric applications.This work provides new insights into the elimination of intervalley scat-tering by crystal field splitting and SOC effects,and paves the way for the evaluation of thermoelectric properties of materials with complex scattering mechanisms and strong anharmonicity.展开更多
A series of single-phased Ca2Al2SiOT：EU2＋phosphors were synthesized by the solid-state reaction. Their structure and photoluminescence properties were investigated by the X-ray powder diffraction （XRD） and excitat...A series of single-phased Ca2Al2SiOT：EU2＋phosphors were synthesized by the solid-state reaction. Their structure and photoluminescence properties were investigated by the X-ray powder diffraction （XRD） and excitation and emission spectra in detail. The emission spectra of Ca2Al2SiO7：Eu2＋ phosphors consisted of blue and green band located at 419 and 542 nm, respectively. The relative intensities of the blue and green emission changed with Eu2＋ concentration and were sensitive to the excitation wavelength. The unique photoluminescence property originated from the 4f^7→4f65d transition of Eu2＋ at different energy levels, on which the effect of the crystal field strength was con- sidered to be tailed by adjusting the host composition.展开更多
基金Supported by the Major State Basic Research Development of China(973 Program)(No.2006CB921606)the Ministry of Education(No.309020)
文摘Based on the first-principle calculations for 3D Hofmann-like spin-crossover （SCO） compound [Fe（C4H4N2）{Pt（CN）4}], the discrepancy of transition mechanism is clarified with quantitatively distinguishable evidence of second order phase transition. It shows that the stretch around 0.2 ？ of Fe-N bond length leads to the continuous structure expansion, as the energy splitting ΔEHL between low-spin and high-spin states reduces from 2.554 2 eV to -0.327 8 eV, and the crystal-field splitting （CFS） is reduced from 1.845 8 eV to 0.420 8 eV meanwhile. A physics image relating the calculations results with CFS in the frame of ligand-field theory is presented, which manifests that CFS is a necessary parameter to be introduced directly in the theory of spin-state transition.
文摘Any electronic eigenstate of the paramagnetic ion open-shell is characterized by the three independent multipole asphericities for and 6 related to the second moments of the relevant crystal-field splittings by , where . The Ak as the reduced matrix elements can serve as a reliable measure of the state capability for the splitting produced by the k-rank component of the crystal-field Hamiltonian. These multipolar characteristics allow one to verify any fitted crystal-field parameter set by comparing the calculated second moments and the experimental ones of the relevant crystal-field splittings. We present the multipole characteristics Ak for the extensive set of eigenstates from the lower parts of energy spectra of the tripositive 4 f N ions applying in the calculations the improved eigenfunctions of the free lanthanide ions obtained based on the M. Reid f-shell programs. Such amended asphericities are compared with those achieved for the simplified Russell-Saunders states. Next, they are classified with respect to the absolute or relative weight of Ak in the multipole structure of the considered states. For the majority of the analyzed states (about 80%) the Ak variation is of order of only a few percent. Some essential changes are found primarily for several states of Tm3+, Er3+, Nd3+, and Pr3+ ions. The detailed mechanisms of such Ak changes are unveiled. Particularly, certain noteworthy cancelations as well as enhancements of their magnitudes are explained.
文摘Complexes Cl-RuⅡ（dppe）2（Fe Cl4）·2CH2Cl2（2） and Br-RuII（dppe）2（Fe Br4）·2CH2Cl2（3） were prepared by the reaction of trans-RuII（dppe）2Cl2（1） with FeX 3（X = Cl, Br）. More interestingly, the central Ru atoms of RuII（dppe）-based complexes（2 and 3） define a tetragonal pyramid with five-coordination. The temperature dependence magnetic susceptibilities indicate that the xMT values of complexes 2 and 3 are almost constant at 50~300 K, and the xMT values sharply decrease with further decreasing the temperature at low temperature due to the zero-field splitting（ZFS） of high spin Fe（III） ions.
基金supported by the National Natural Science Foundation of China(62275053,61775042,11674062,11374063)Shanghai Municipal Natural Science Foundation under Grant Nos.19ZR1402900 and the Fudan University-CIOMP Joint Fund(FC2017-003).
文摘The electron-phonon(el-ph)and phonon-phonon interactions play a key role in determining electronic and thermal transport properties,respectively,in promising two-dimensional(2D)semiconductor de-vices.In this study,we investigated el-ph interactions using Wannier-Fourier interpolation method and renormalized phonon scattering considering finite-temperature effects in Bi_(2)TeSe_(2)monolayer.The re-sults show that the optical phonon modes dominate the carrier scattering,where level repulsion induced by crystal field splitting and spin-orbit coupling(SOC)effect effectively suppresses intervalley scattering,leading to high hole mobility.Moreover,the strong anharmonicity in Bi_(2)TeSe_(2)monolayer results in the temperature-dependent softening of its optical phonons,along with a corresponding variation in interatomic force constants(IFCs).As a result,the lattice thermal conductivity is remarkably low and exhibits weak temperature dependence.Finally,the predicted dimensionless thermoelectric figure of merit exceeds unity in the range of 200-800 K,indicating the potential of Bi_(2)TeSe_(2)monolayer for thermoelectric applications.This work provides new insights into the elimination of intervalley scat-tering by crystal field splitting and SOC effects,and paves the way for the evaluation of thermoelectric properties of materials with complex scattering mechanisms and strong anharmonicity.
基金Project supported by the Specialized Research Fund for the Doctoral Program of Higher Education of China (20115314120001) the Special Program for National Program on Key Basic Research Project of China (973 Program) (2011CB211708) the Foundation of Natural Science of Yunnan Province (2011FB022)
文摘A series of single-phased Ca2Al2SiOT：EU2＋phosphors were synthesized by the solid-state reaction. Their structure and photoluminescence properties were investigated by the X-ray powder diffraction （XRD） and excitation and emission spectra in detail. The emission spectra of Ca2Al2SiO7：Eu2＋ phosphors consisted of blue and green band located at 419 and 542 nm, respectively. The relative intensities of the blue and green emission changed with Eu2＋ concentration and were sensitive to the excitation wavelength. The unique photoluminescence property originated from the 4f^7→4f65d transition of Eu2＋ at different energy levels, on which the effect of the crystal field strength was con- sidered to be tailed by adjusting the host composition.
