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1.
Guangtao Wang Minping Zhang Lihua Zheng Zongxian Yang 《Solid State Communications》2011,151(18):1231-1235
The electronic structure and magnetic properties of new layered oxyselenide compounds La2O3Fe2Se2 and La2O3Co2Se2 are studied by first-principles calculations. Our results indicate that both compounds are Mott-insulators with orbital ordering. The ground states of both compounds are the checkerboard antiferromagnetic states, which are different from the iron pnictide superconductors, although their structures are similar to those of the Fe-As-based superconductors. 相似文献
2.
Incommensurate modulations in Ba2TiSi2O8, Sr2TiSi2O8, and Ba2TiGe2O8 are compared based on their corresponding electron diffraction patterns. The dependence of the modulations on chemical composition provides a suitable model system for the investigation of incommensurations in framework structures using high-resolution transmission electron microscopy (HRTEM). A widening of quantitative HRTEM utilising the concept of rigid units is proposed allowing for a determination of atomistic displacements responsible for the formation of incommensurately modulated structures. 相似文献
3.
Magnetometric and neutron diffraction studies of polycrystalline NdCo2GE2, ErCo2Ge2 and PrFe2Ge2 compounds were carried out in the temperature range between 4.2 and 300 K. All samples are antiferromagnetic with Néel temperature 26.5, ~ 4.2 and 13 K, respectively. The RECo2Ge2 compounds have collinear antiferromagnetic order of +?+? type. For PrFe2Ge2 a sinusoidal magnetic structure is observed. Magnetic moment is localized on RE atoms only and is equal to that of RE3+ free ion value. In ErCo2Ge2 the magnetic moment of Er atoms is perpendicular to the c-axis, whereas for remaining compounds it is parallel to the c-axis. 相似文献
4.
A. Szytu∤a M. S̀laski H. Ptasiewicz-Ba̧k J. Leciejewicz A. Zygmunt 《Solid State Communications》1984,52(4):395-398
Neutron diffraction and magnetization study of polycrystalline NdRh2Si2 and ErRh2Si2 was performed in the temperature range from 4.2 to 293 K. Both compounds are of ThCr2Si2 type crystal structure and exhibit antiferromagnetic ordering below TN = 53 K and TN = 12.8 K respectively. The magnetic structure wave vector is τ = [0, 0, 1]. 相似文献
5.
Keiichi MinamiAkitoshi Hayashi Satoshi UjiieMasahiro Tatsumisago 《Solid State Ionics》2011,192(1):122-125
Electrical and electrochemical properties of the 70Li2S·(30 − x)P2S5·xP2S3 and the 70Li2S·(30 − x)P2S5·xP2O5 (mol%) glass-ceramics prepared by the mechanical milling technique were investigated. Glass-ceramics with 1 mol% P2S3 and 3 mol% P2O5 showed the highest conductivity of 5.4 × 10− 3 S cm− 1 and 4.6 × 10− 3 S cm− 1, respectively. Moreover, these glass-ceramics showed higher electrochemical stability than the 70Li2S·30P2S5 (mol%) glass-ceramic. From the XRD patterns of the obtained glass-ceramics, trivalent phosphorus and oxygen were incorporated into the Li7P3S11 crystal. We therefore presume that the Li7P3S11 analogous crystals, which were formed by incorporating trivalent phosphorus and oxygen into the Li7P3S11 crystal, improve the electrical and electrochemical properties of the glass-ceramics. An all-solid-state cell using the 70Li2S·29P2S5·1P2S3 (mol%) glass-ceramic as solid electrolyte operated under the high current density of 12.7 mA cm− 2 at the high temperature of 100 °C. The cell showed an excellent cyclability of over 700 cycles without capacity loss. 相似文献
6.
A neutron diffraction study of polycrystalline PrCu2Si2 [1], PrCu2Ge2 [2], PrFe2Ge2 [3] and NdFe2Ge2 [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below TN = 19 ± 1 K [1], TN = 16 ± 1 K [2], TN = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu2Si2 and PrCu2Ge2 and +--+ for PrFe2Ge2 and NdFe2Ge2. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field. 相似文献
7.
Junji Awaka Norihito Kijima Shoichi Nagata 《Journal of Physics and Chemistry of Solids》2008,69(7):1740-1746
High-purity powder specimens of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 have been successfully synthesized by solid-state chemical reaction. The Rietveld refinements from X-ray powder diffraction data verified that these compounds have the garnet-type structure (space group , No. 230) with the lattice constant of a=12.596(2) Å for AgCa2Mn2V3O12 and a=12.876(2) Å for NaPb2Mn2V3O12. Calculation of the bond valence sum supported that Mn is divalent and V is pentavalent in these garnets. Estimation of the quadratic elongation and the bond angle variance showed that the distortions of the MnO6 octahedra and the VO4 tetrahedra are significantly suppressed. Our new results of AgCa2Mn2V3O12 and NaPb2Mn2V3O12 are compared to those of AgCa2M2V3O12 and NaPb2M2V3O12 (M=Mg, Co, Ni, Zn). 相似文献
8.
9.
In this paper, we present the spectral results of Dy3+ and Pr3+ (1.0 mol%) ions doped Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (Tg), crystallization (Tc) and melting (Tm) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy3+:glass has shown two emission transitions 4F7/2→6H15/2 (482 nm) and 4F7/2→6H13/2 (576 nm) with an excitation at 390 nm wavelength and Pr3+:glass has shown a strong emission transition 1D2→3H4 (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy3+ and Pr3+ glasses have shown bright yellow and reddish colors, respectively, from their surfaces. 相似文献
10.
Rajendra Kumar Singh 《Journal of magnetism and magnetic materials》2009,321(18):2749-2752
Glass-ceramics have been derived from 4.5MgO(45−x)CaO34SiO216P2O50.5CaF2xFe2O3 (x=5, 10, 15, 20 wt%) glasses by heat treatment. Room temperature electron paramagnetic resonance (EPR) spectra and temperature-dependent magnetic susceptibility (χ) of the glass-ceramics have been obtained. The EPR absorption line centered at g≈4.3 disappeared at higher concentrations of iron oxide. The intensity and line width of the EPR absorption line centered at g≈2.1 increased as the iron oxide concentration was increased. Temperature-dependent magnetization of samples with low iron oxide content revealed ferrimagnetic as well as paramagnetic contributions. Information about the structural changes involving iron ions, their valence state and the type of magnetic interactions between the Fe ions as a function of composition was obtained using EPR and χ studies. 相似文献
11.
M. Rams A. ZarzyckiA. Pikul K. Tomala 《Journal of magnetism and magnetic materials》2011,323(11):1490-1494
The magnetic properties of R2Ru2O7 pyrochlore compounds (R=Yb, Dy) were studied using specific heat down to 0.4 K and bulk magnetic measurements. These two rare-earth elements were chosen to demonstrate the effect of Ru-R exchange interaction on R magnetic sublattice, in two cases of anisotropy: axial in Dy and planar in Yb. Dy2Ru2O7 undergoes a second order transition to a fully ordered state at 1.85 K with no signs of the spin-ice state. In Yb2Ru2O7 the Yb sublattice orders gradually around 8 K due to the Ru molecular field and no further transition is observed down to 0.4 K. Including the Ru molecular field at the R site in calculations based on crystal field parameters known from titanates R2Ti2O7, allowed us to interpret experimental data. 相似文献
12.
Richard J. Colton J.Wayne Rabalais 《Journal of Electron Spectroscopy and Related Phenomena》1974,3(5):345-357
Photoelectron and electronic absorption spectra of SCl2, S2Cl2, S2Br2, and (CH3)2S2 have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MO's are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential. 相似文献
13.
I. V. Silkin Yu. M. Koroteev S. V. Eremeev G. Bihlmayer E. V. Chulkov 《JETP Letters》2011,94(3):217-221
The electronic structure of ternary compounds Pb2Sb2Te5, Pb2Bi2Te5, and Pb2Bi2Se5, which have a layered structure that consists of nine-layer atomic blocks separated by van der Waals gaps, has been theoretically
studied. It has been shown that all studied compounds are three-dimensional topological insulators. The possibility of the
existence of a two-dimensional topological insulator has been found in ultrathin (0001) Pb2Sb2Te5 and Pb2Bi2Te5 films. Oscillations of the ℤ2 topological invariant with an increase in the film thickness have been observed in the latter compound. 相似文献
14.
J.K. Yakinthos Ch. Routsi Penelope Schobinger-Papamantellos 《Journal of Physics and Chemistry of Solids》1984,45(6):689-693
Neutron diffraction studies of polycrystalline PrCo2Si2 and TbCo2Si2 compounds were carried out at 4.2 and 293 K. Both samples have collinear antiferromagnetic order below TN(31(1) and 46(1) K for Pr and Tb compound respectively), with their magnetic moments parallel to the c axis. The ordered magnetic moment values of Pr and Tb at 4.2 K (3.19 and 9.12 μB respectively), are close to the saturation value of the free ions. The corresponding magnetic space group Pl4/mnc (Sh410128) is body-anticentered ( refering to Pl cell). 相似文献
15.
Two sets of crystal field (CF) parameters have been proposed for DyFe2Si2, none of which could provide a simultaneous explanation of the available experimental data, particularly at low temperatures (below 100 K). The set derived from magnetic studies could not even explain the thermal variation of the magnetic specific heat reported in the same work. Although the set of CF parameters, obtained from a fit to the Mossbauer spectra, could provide a fairly good explanation of the thermal variation of the magnetic susceptibilities along the c-axis, it could not explain the observed thermal variation of other reported experimental findings. In the present work, an appraisal of the CF parameters proposed earlier has been done and a set of CF parameters has been derived, which provide a simultaneous explanation of all the available experimental data. The effect of substitution of Ge for Si on the magnetic properties and the magnetic specific heat of DyFe2Si2 has been studied in the framework of one electron crystal field model. The inelastic neutron scattering studies and EPR measurements are required to check the predicted Stark energies and the paramagnetic resonance g-values. 相似文献
16.
Dariush Souri Mohammad Elahi Mohammad S. Yazdanpanah 《Central European Journal of Physics》2008,6(2):306-310
The ternary 70P2O5-10Li2MoO4-20Li2O and 70P2O5-10Na2MoO4-20Na2O glasses, prepared by the press-melt quenching technique, were studied at temperatures between 298 and 418 K for their high
dc electric field properties. For the above purpose, the effect of a strong electric field on the dc conduction of these amorphous
bulk samples was investigated using the gap-type electrode configuration. At low electric fields, the current-voltage (I — V) characteristics have a linear shape, while at high electric fields (> 103 V/cm), bulk samples show nonlinear effects (nonohmic conduction). Current-voltage curves show increasing departure from Ohm’s
law with increasing current density, leading to critical phenomena at a maximum voltage (threshold voltage), known as switching
(switch from a low-conduction state to a higher-conduction state at threshold voltage). The Pool-Frenkel high-field effect
was observed at electrical fields of about 103–104 V/cm; then the lowering factor of the potential barrier, the high frequency dielectric constant, and the refractive index
of these glasses were determined.
相似文献
17.
The behavior of the desorbing F+ ion current from electron bombarded CCl2F2, C2H2F2 and C2F6 adsorbed on tungsten has been used to investigate the processes of adsorption and desorption of these gases. For tungsten near room temperature, measurements of the F+ ion current as a function of electron bombardment time indicated very similar or even identical F+-yielding adsorbed species resulting from adsorption of either CCl2F2 or C2H2F2 and widely different species from C2F6. Cl+ ions were also observed to desorb from CCl2F2 ad-layers. The behavior of the Cl+ ion current with time during electron bombardment indicated electronic conversion between adsorbed binding modes. Complementary investigations on the interaction of CCl2F2, C2H2F2 and C2F6 with tungsten were carried out by thermal desorption experiments in which the F+ ion signal was used to observe the coverage decrease of the F+-yielding species. The experiments were performed at tungsten temperatures in the 1200–1600 K range. It was concluded that the F+-yielding adsorbed species from CCl2F2 and C2H2F2 were strongly bound to the tungsten surface. The F+-yielding species from C2F6 were found to be weakly bound. From a comparison of the ESD and thermal desorption results, the possibility of dissociative adsorption as well as the nature of the adsorbed species is discussed. 相似文献
18.
The compounds SrBe2Si2O7 and BaBe2Si2O7 both have the barylite structure. With 254 nm excitation, the Eu2+-activated compounds give UV emission peaking at 360 nm (Sr) and at 375 nm (Ba). Maximum quantum efficiencies of 40% (Sr) and 65% (Ba) were measured. The emission consists of a 5d-4f band emission as well as 4f-4f line emission, in contrast to many other Eu2+-activated oxides which generally show only 5d-4f band emission. At 77°K, both compounds show only the 4f-4f line emission peaking at 360 nm. At higher temperatures, 5d-4f band emission shows up at the cost of the line emission. A thermal equilibrium is assumed between the lowest excited 5d and 4f levels. The energy difference between these levels, calculated from the variation in the line-band intensity ratio with temperature, was computed to be 0.15 eV (Sr) and 0.09 eV (Ba). The occurrence of the line emission in the barylites is correlated with the weakness of the crystal field at the Eu2+ ions and with the high quenching temperature of the 5d-4f band emission. 相似文献
19.
Yoshio Tatamitani 《Journal of Molecular Spectroscopy》2007,242(2):150-155
The results of molecular beam Fourier transform microwave (FTMW) investigations of the van der Waals complexes of difluoromethane with 1,1-difluoroethene (DFE) and trifluoroethene (TFE) are reported. The rotational parameters of the complexes have been interpreted in terms of a Cs geometry with the two H or F atoms of CH2F2 lying out of the σv symmetry plane of the complexes. The complexes are bound by three hydrogen bonds, of which one is the stronger C-F?H-C type, and two are the weaker C-H?F?H-C or C-F?H?F-C types for DFM-DFE or DFM-TFE, respectively. The most notable difference in the two complexes is that the out of plane atoms are two hydrogens for DFM-DFE, but are two fluorines for DFM-TFE. Additional information on the structure and hydrogen bonding has been obtained from ab initio calculations. 相似文献
20.
J. J. Lin W. Y. Lin R. F. Tsui 《Physica C: Superconductivity and its Applications》1993,210(3-4):455-462
We have measured the resistivities of Al2O3-Bi2Sr1.8Ca1.2Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy composites with the nominal Bi2Sr1.8Ca1.2Cu2Oy volume fraction, 2212, ranging from 0.15 to 1.00. For the Al2O3-Bi2Sr1.8Ca1.2Cu 2Oy composites, we find for the samples with 2212≥0.6 that the superconducting transition temperature, Tc, is not disturbed by the addition of Al2O3. For 2212<0.3, no zero-resistivity state is observed. For the MgO-Bi2Sr1.8Ca1.2Cu2Oy composites, Tc is barely disturbed for the samples with ρ2212≥0.7. No superconducting state is observed for the samples with ρ2212<0.35. The variation of (300 K) with ρ2212 indicates a three-dimensional percolating Bi-Sr-Ca-Cu-O matrix occurring at ρ2212≈0.19 and ≈0.15 in Al2O3-Bi2Sr1.8Ca1.2 Cu2Oy and MgO-Bi2Sr1.8Ca1.2Cu2Oy, respectively. Both resistivity and magnetization measurements suggest that the reactions of Bi2Sr1.8Ca1.2Cu2Oy with MgO are weaker than with Al2O3. 相似文献