共查询到20条相似文献,搜索用时 12 毫秒
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ukasz Gondek Dariusz Kaczorowski Andrzej Szytua 《Solid State Communications》2009,149(47-48):2181-2184
Magnetic, electrical transport and heat capacity measurements have been performed on polycrystalline sample of the compound TmRu2Si2, which crystallizes with the tetragonal ThCr2Si2-type crystal structure. The results show paramagnetic behaviour down to 0.3 K, at variance with the literature data. On the basis of the collected data, possible origins of non-magnetic behaviour are discussed. Mixed valence of Tm ions or hybridisation between Tm 4f and Ru 4d states are the most probable reasons for paramagnetic behaviour of the TmRu2Si2. 相似文献
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We have performed first-principles calculations to investigate the pressure effects on CaFe2As2 and BaFe2As2. Our calculations show that in CaFe2As2, the orthorhombic structure transforms to a collapsed tetragonal structure at 0.4 GPa with a volume collapse of 9.5%, which is in agreement with experiments. Together with the structural phase transition, CaFe2As2 undergoes a magnetic transition from the stripe antiferromagnetic ordering to the nonmagnetic state. For BaFe2As2, we predict that the orthorhombic structure transforms to the tetragonal structure at 9.4 GPa. Unlike CaFe2As2, the magnetic moments of Fe ions in BaFe2As2 are not zero and the stripe antiferromagnetic ordering transforms to the checkerboard antiferromagnetic ordering together with the structural phase transition. The stability of the orthorhombic structure up to 9.4 GPa suggests that superconductivity and magnetism coexist in BaFe2As2. 相似文献
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N. Mandal F.C. Peiris O. Maksimov M.C. Tamargo 《Solid State Communications》2009,149(39-40):1698-1701
We have used spectroscopic ellipsometry to determine the complex dielectric function of a series of ternary BexZn1−xTe thin films grown by molecular beam epitaxy. The II–VI semiconductor alloys were grown on InP substrates that had an InGaAs buffer layer. After the growth, X-ray diffraction experiments were performed in order to determine the alloy concentration. A standard inversion technique was used to obtain the dielectric functions from the measured ellipsometric spectra, obtained between 2000 nm (5000 cm−1) and 40,000 nm (250 cm−1). By modelling the dielectric function as a collection of oscillators, representing longitudinal and transverse optical phonons of the BexZn1−xTe lattice, we were able to recover the phonon spectra for this alloy system. It is argued that the additional phonon modes that are obtained from ellipsometry are best understood from the recently-proposed percolation model. 相似文献
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The structural and elastic properties of perovskite-type RCRh3, with R=Sc, Y, La and Lu, under pressure effects have been investigated using the pseudo-potential plane-wave method based on the density functional theory within the generalized gradient approximation. For monocrystalline RCRh3, the optimized lattice constants, elastic constants and directional elastic wave velocities are calculated and analyzed in comparison with the available experimental and theoretical data. An increase in the lattice constant has been found with increasing atomic size of the R element and a corresponding decrease in the hardness. The anisotropic elastic constants and directional elastic wave velocities increase linearly with increasing pressure. A set of elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, Lamé’s coefficients, average sound velocity and Debye temperature are predicted in the framework of the Voigt–Reuss–Hill approximation for polycrystalline RCRh3. We have found that the toughness of RCRh3 compounds can be improved at high pressure. 相似文献
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Amauri J. Paula Rodrigo Parra Maria A. Zaghete Jos A. Varela 《Solid State Communications》2009,149(39-40):1587-1590
Because of the environmental concerns, the manufacture of ceramics based on lead titanate zirconate [Pb(Zr1−xTix)O3−PZT] has been condemned because of the lead toxicity. In this context, the electromechanical properties of sodium, potassium and lithium niobate [(Na0.5−x/2K0.5−x/2Lix)NbO3−NKLN] at the morphotropic phase boundary granted these materials the position of most suitable candidate to replace PZT. However, the production of these ceramics is rather critical mainly because of a natural tendency of forming secondary phases. To help with the studies of the synthesis of this lead-free piezoceramic, this work presents an evaluation of the crystallization of the (Na0.47K0.47Li0.06)NbO3 phase by solid-state reactions. TG-DTA, XRD, dilatometric and ferroelectric hysteresis analyses indicated that a secondary phase (K3Li2Nb5O15) crystallizes at temperatures above 850 C and also during the sintering of the powders compacts at 1080 C. To prevent the formation of this phase, the addition of Na2Nb2O6.nH2O microfibers obtained through a microwave hydrothermal synthesis was performed in the sintering process. After to this addition, the suppression of the K3Li2Nb5O15 phase occurred and an increase of the NKLN electrical properties was then obtained. 相似文献
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R.W. Wang J. Liu Y.B. Li D.J. Wang Y.H. Wang Y.W. Li 《Solid State Communications》2009,149(47-48):2215-2218
Magnetic transitions and magnetotransport properties of polycrystalline Tb1−xGdxMn6Ge6 (x=0.2–1.0) compounds have been investigated by magnetic property and resistivity measurements in an applied magnetic field up to 50 kOe. The cell parameter a,c and cell volume V of compounds (x=0.2–1.0) increase with an increasing Gd content. The compounds (x=0.2–1.0) show a rich variety of magnetic behavior, such as antiferromagnetic, ferrimagnetic and paramagnetic state with increasing temperature. Their Curie temperatures increase almost linearly with an increasing Gd content from 460 K for x=0.2 to 484 K for x=1.0. The compounds (x=0.2–1.0) display the field induced metamagnetic transitions, and the threshold fields first increase and then decrease with an increasing Gd content. The magnetoresistance curves of the Tb0.4Gd0.6Mn6Ge6 compounds in an applied magnetic field up to 50 kOe are presented and the magnetoresistance effects are related to the metamagnetic transitions. 相似文献
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《Physics letters. [Part B]》2009,670(4-5):292-299
We present a measurement of the cross section for Z boson production times the branching fraction to tau lepton pairs in collisions at . The measurement is performed in the channel in which one tau lepton decays into a muon and neutrinos, and the other tau lepton decays hadronically or into an electron and neutrinos. The data sample corresponds to an integrated luminosity of 1.0 fb−1 collected with the DØ detector at the Fermilab Tevatron Collider. The sample contains 1511 candidate events with an estimated 20% background from jets or muons misidentified as tau leptons. We obtain , which is consistent with the standard model prediction. 相似文献
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The tree-level contributions to the rare decays , , and are analyzed and compared to those occurring in , , and . It is shown that these purely long-distance contributions, arising from the exchange of a charged lepton, can be significant in B+ decays for an intermediate τ, potentially blurring the distinction between the modes used to extract B+→τ+ντ and those used to probe the genuine short-distance and FCNC transitions. Numerically, the tree-level contributions are found to account for 98%, 12% and 14% of the total , , and rates, respectively. 相似文献
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Y.S. Zhang K.L. Yao Z.L. Liu X.L. Wang L.H. Yu 《Solid State Communications》2009,149(47-48):2260-2263
We perform a theoretical investigation on the magnetism and orbital hybridization in ternary germanide Ce3Ni2Ge7 using the full-potential linearized augmented plane wave method (FP_LAPW) based on the density functional theory (DFT). The calculation with local spin density approximation (LSDA) predicts that there are two states for the Ce atoms due to the different environment: one (Ce1) is near the nonmagnetic state and the other (Ce2) is localized and magnetic. The orbital hybridization plays a key role in determining the state of Ce. On adding on-site Coulomb potential to the localized Ce2-4f orbit, the magnetic moment obtained from our calculation fits well with the experimental value. 相似文献
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The electronic structure and the 119Sn and121Sb Mössbauer parameters of Sb-doped SnO2 were calculated using a first-principles method. We show that substitution of Sn by Sb leads to a small decrease of the distances between the dopant and the six oxygen first-nearest neighbours. The most important modifications in the electronic structure are related to the bottom of the conduction band, which has Sb 5s, Sn 5s and O 2p characters. By considering two supercell sizes and charged supercells we show that antimony oxidation state is Sb5+ and we explain the origin of the Mössbauer parameters from the local electronic structure of the cations. 相似文献
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Structural changes of Cu51–Cu56 clusters during freezing have been studied by employing molecular dynamics(MD) simulations. With the growth of the crystallization phase, local patterns in different regions determined by the atom density profiles present different characteristic for these studied clusters. While the atom movements in the even-number clusters result in the formation of initial two-shell, then three-shell, and finally four-shell structures, the atoms in the odd-number clusters, with one exception of the Cu51 cluster, first move into the central region and the outermost parts, then follow the movement from the inner parts into the outer parts. The crystallization temperature of these clusters has an oscillatory increase behavior for odd- and even- numbered copper atoms with increasing cluster size. 相似文献
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First-principles calculations of the crystal structure and the elastic properties of OsN2 have been carried out with the plane-wave pseudopotential density functional theory method. The calculated values are in very good agreement with experimental data as well as with some of the existing model calculations. The dependence of the elastic constants cij, the aggregate elastic moduli (B,G,E), Poisson’s ratio, and the elastic anisotropy on pressure has been investigated. Moreover, the variation of the Debye temperature and the compressional and shear elastic wave velocities with pressure P up to 60 GPa at 0 K have been investigated for the first time. 相似文献
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《Physics letters. [Part B]》2008,663(4):418
Rare decay modes , J/ψ→D−π++c.c., and are searched for using events collected with the BESII detector at the BEPC. No signal above background is observed. We present upper limits on the branching fractions of , B(J/ψ→D−π+)<7.5×10−5, and at the 90% confidence level. 相似文献