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1.
《Journal of magnetism and magnetic materials》1987,67(2):232-238
The crystal structures and the physical properties of U4M7Ge6 (M = Ru, Os) and UM2Ge2 (M = Rh, Ir) have been investigated. The former crystallize in the cubic structure of U4Re7Si6; U4Ru7Ge6 orders ferromagnetically at TC ≈ 10–13 K whereas U4Os7Ge6 remains paramagnetic down to 4.2 K. The latter whise structures derive from the tetragonal ThCr2Si2 or CaBe2Ge2 types display limited homogeneity ranges; URh2Ge2 exhibits a dense-Kondo behaviour at low temperatures; UIr2Ge2 shows polymorphism and its physical properties are strongly influenced by its crystal structure. 相似文献
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Magnetic properties,electronic structure,and optical properties of the filled skutterudite BaFe4Sb12
The magnetic properties, electronic structure, and optical properties of the filled skutterudite BaFe4Sb12 are calculated by the first-principles full-potential linearized augmented plane wave (FPLAPW) plus local orbital method. It is found that the local spin density approximation (LSDA) method appears more accurate than the generalized gradient approximation (GGA) method in calculating the electronic structures and optical properties of this compound. Furthermore, our calculated lattice constant and spin magnetic moments with the LSDA method are in overall better agreement with experiment. In contrast with recent experiment, our calculations are in good agreement with experimental reflectivity spectra and optical conductivity spectrum. 相似文献
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Jiří Růžička 《Zeitschrift für Physik A Hadrons and Nuclei》1970,237(5):432-441
Superconducting samples of the nominal composition Nb x (Al1?y , Ge y )1?x withx reaching from 0.72 to 0.78 andy from 0.175 to 0.30 were prepared and the superconducting transitions of as-cast and of annealed samples were measured. The onset of superconductivity for samples with a suitable composition and annealing procedure has been observed to be at about 21.05 K. By the help of anodic oxydation process and by multichannel semiconductor x-ray spectroscopy with scanning electron microscope it has been possible to carry out the phases distribution and detailed phase-analysis in the samples. 相似文献
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Ca3Al2M3O12(M=Si,Ge)石榴石中Ce^3+离子的荧光光谱 总被引:7,自引:0,他引:7
本文研究了Ca3Al2M3O12(M=Si,Ge)石榴石中Ge^3+离子的荧光光谱。在这两种石榴石中,Ce^3+的发射光谱均为Ce^3+的5d→4f能级跃迁发射宽谱带,但有很大差异。在锗酸盐中,Ce^3+的发射强度很弱,而在硅酸盐中发射强,295和77K下在Ca3Al2Si3O12中Ce^3+的荧光寿命分别为46和49ns。Gd^3+和助溶剂的引入可提高Ce^3+的发射强度。 相似文献
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P. Rogl B. Chevalier M.J. Besnus J. Etourneau 《Journal of magnetism and magnetic materials》1989,80(2-3):305-310
From X-ray Guinier powder data the crystal structures of the ternary germanides Ce(Rh or Ir)Ge and Ce(Pd or Pt)Ge were confirmed to be of the TiNiSi-type and the CeCu2-type, respectively. Magnetic, electrical and thermodynamic properties of these materials have been studied in the temperature range 1.5 K T 300 K. CeRhGe orders antiferromagnetically below 9.3 K, whereas in CeIrGe cerium is in an intermediate valence state and no magnetic transition is observed down to 1.5 K. Resistivity and specific heat measurements reveal a magnetic transition near 3.4 K for both CePdGe and CePtGe. According to the present investigations the compounds CeMGe, with M = Rh, Pd, Pt are classified as magnetically ordered Kondo systems. 相似文献
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A. P. Menushenkov A. A. Yaroslavtsev I. A. Zaluzhnyy A. V. Kuznetsov R. V. Chernikov N. Yu. Shitsevalova V. B. Filippov 《JETP Letters》2013,98(3):165-169
The parameters of the local crystal structure of dodecaborides RB12 (R = Ho, Er, Tm, Yb, Lu) have been determined by extended X-ray absorption fine structure (EXAFS) spectroscopy. It has been shown that the vibrations of the rare-earth ion with respect to the boron cage are well described in the harmonic approximation. At the same time, the displacement of rare-earth ions from equilibrium positions of the crystal structure should be taken into account to determine the length of the R-B bond. The analysis of EXAFS spectra has revealed the displacement of 1–6% of rare-earth ions by about 0.2–0.3 Å in all compounds under investigation; this displacement at low temperatures results in the formation of a cage glass phase. 相似文献
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Sichelschmidt J Voevodin V Im HJ Kimura S Rosner H Leithe-Jasper A Schnelle W Burkhardt U Mydosh JA Grin Y Steglich F 《Physical review letters》2006,96(3):037406
Optical investigations are presented of the filled skutterudites AFe4Sb12 with divalent cations A=Yb, Ca, Ba. For each of these compounds a very similar pseudogap structure in the optical conductivity develops in the far-infrared spectral region at temperatures below 90 K. Highly accurate local-density approximation electronic band structure calculations can consistently explain the origin of the pseudogap structure generated largely by transition metal 3d states. In particular, a 4f-conduction electron hybridization or strong correlations can be ruled out as origin for the pseudogap. 相似文献
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D. V. Volkov A. A. Demidov N. P. Kolmakova L. V. Takunov 《Physics of the Solid State》2008,50(9):1677-1680
Crystal field effects in rare-earth ferroborates RFe3(BO3)4 with various rare-earth elements are studied theoretically. The rare-earth magnetoelastic interaction Hamiltonian is written in a multipole approximation. The field and temperature dependences of the multipole moments and strain susceptibilities of rare-earth ions in the ferroborate structure are calculated. A comparative analysis of anomalies in the thermal expansion and elastic constants of rare-earth ferroborates with Tb and Dy ions having identical magnetic structure but differing in the degree of anisotropy of the rare-earth ion is performed. 相似文献
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The elastic, electronic, magnetic and optical properties of filled skutterudite ROs4P12 (R = Sm, Eu and Gd) have been studied by first principles calculation. The full-potential linearized augmented plane wave method based on density functional theory was employed. For the exchange-correlation potential, local spin density approximation + Coulomb repulsion (LSDA + U) is used to treat the f-electrons more effectively. The numerical values of the elastic parameters are estimated in the framework of the Voigt–Reuss–Hill approximation. OsP-based filled skutterudite with localized 4f and 5d-electrons shows dense energy bands near Fermi energy originating from rare earth and Os atoms. The dense density of states near EF reveals that these compounds are suitable for thermoelectric application. Optical constants including dielectric function, optical reflectivity and refractive index are calculated for photon energy radiation up to 12 eV. The exchange-splitting of R-4f states were analyzed to explain the ferromagnetic behavior of ROs4P12. 相似文献
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I. Grigoraviciute 《Solid State Communications》2006,137(11):601-605
Here two new high-Tc superconductors are reported of the (Cu,M)-1232 structure containing a fluorite-structured (Ce,Y)-O2-(Ce,Y)-O2-(Ce,Y) triple-layer block between two adjacent superconductive CuO2 planes. The new superconductors were found through substitution studies at the Mo site in the recently synthesized superconductor, (Cu0.75Mo0.25)Sr2(Ce0.67Y0.33)3Cu2O11+δ or (Cu0.75Mo0.25)-1232 [Y. Morita, T. Nagai, Y. Matsui, H. Yamauchi, M. Karppinen, Phys. Rev. B 70 (2004) 174515. [10a]]. Essentially single-phase samples of the (Cu0.75M0.25)-1232 phase with M=W, Re and Pb were obtained by an ambient-pressure solid-state synthesis method. Through a subsequent high-pressure oxygenation (HPO) treatment carried out at 5 GPa and 500 °C in the presence of Ag2O2 as an oxygen source the M=W and Re samples were successfully ‘superconductorized’. Introduction of Pb was found to markedly enhance the speed of the formation of the 1232 phase, but the (Cu,Pb)-1232 samples did not exhibit superconductivity. Among the superconductive (Cu,M)-1232 samples, the highest Tc value of 56 K was achieved for (Cu0.75Re0.25)-1232. It is likely that the higher the average valence of cations in the (Cu,M)O1+δ charge-reservoir is, the more can the phase accommodate excess oxygen upon HPO treatment and the higher is the resulting Tc value. 相似文献
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The structural stability of Alkali metal hydrides AMH4 (A=Li, Na; M=B, Al) is analyzed among the various crystal structures, namely hexagonal (P63mc), tetragonal (P42/nmc), tetragonal (P-421c), tetragonal (I41/a), orthorhombic (Pnma) and monoclinic (P21/c). It is observed that, orthorhombic (Pnma) phase is the most stable structure for LiBH4, monoclinic (P21/c) for LiAlH4, tetragonal (P42/nmc) for NaBH4 and tetragonal (I41/a) for NaAlH4 at normal pressure. Pressure induced structural phase transitions are observed in LiBH4, LiAlH4, NaBH4 and NaAlH4 at the pressures of 4 GPa, 36.1 GPa, 26.5 GPa and 46 GPa respectively. The electronic structure reveals that these metal hydrides are wide band gap insulators. The calculated elastic constants indicate that these metal hydrides are mechanically stable at normal pressure. 相似文献
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The optical properties of the SrFX (X=Cl, Br, I) compound have been reported using the full potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2K code. We employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for band structure calculations. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Γ resulting in a direct energy gap. We present calculations of the frequency-dependent complex dielectric function ε(ω) and its zero-frequency limit ε1(0). We find that the value of ε1(0) increases on decreasing the energy gap. The reflectivity spectra and absorption coefficient have been calculated and compared with the available experimental data. 相似文献
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S. Q. Bai X. Y. Huang L. D. Chen W. Zhang X. Y. Zhao Y. F. Zhou 《Applied Physics A: Materials Science & Processing》2010,100(4):1109-1114
Alkaline-earth (AE) and rare-earth (RE) atoms are usually used as void fillers in the caged compound CoSb3 to improve the thermoelectric performance of the filled system. Polycrystalline single-filled Sr0.21Co4Sb12, double-filled Sr
x
Yb
y
Co4Sb12, and Sr
x
Ba
y
Co4Sb12 skutterudites have been synthesized. Rietveld structure refinement confirms that both Sr and Yb occupy the Sb-icosaedron
voids in skutterudite frame work. In this paper, we report the high-temperature thermoelectric properties including electrical
conductivity, Seebeck coefficient, and thermal conductivity. Double filling of the Sr–Yb combinations shows a stronger suppression
on lattice thermal conductivity than that of Sr–Ba combination. Furthermore, the double-filled Sr
x
Yb
y
Co4Sb12 skutterudites exhibit a much higher power factor than the Sr-filled system. The maximum power factor for Sr0.22Yb0.03Co4Sb12.12 reaches 41 μW cm−1 K−2 at room temperature and 57.5 μW cm−1 K−2 at 850 K, respectively. The enhanced thermoelectric figures of merit are 1.32 for Sr
x
Yb
y
Co4Sb12 and 1.22 for Sr
x
Ba
y
Co4Sb12 at 850 K, respectively. 相似文献
16.
R. D. Nevmyvako N. A. Zhuravlev T. A. Denisova Yu. M. Kadyrova K. N. Mikhalev E. G. Khaikina S. F. Solodovnikov 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(4):264-266
Nuclear magnetic resonance (magic angle spinning) spectra of 7Li, 27Al, 87Rb, and 133Cs nuclei are measured in Li2 M 3Al(MoO4)4 triple molybdates (M = Rb, Cs) for the first time. Analysis of the nuclear magnetic resonance spectra reveal considerable asymmetry in the distribution of the electric charge throughout the crystal lattices of the compounds. 相似文献
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本文采用UB3LYP/6-311G(2d)+SDD//CCSD(T)/6-311+G(2d)+SDD方法, 计算研究了气相中碱土金属氧化物阳离子2MO+(M=Ca, Sr, Ba)参与N2O (X1∑+) + CO (X1∑+) → N2 (X1∑+g) + CO2 (X1∑+g) 的反应机理. 通过计算亲氧性得到在三种氧化物阳离子中只有2CaO+从N2O得到O原子并传递给CO的过程是热力学允许的. 碱土金属氧化物阳离子2MO+参与主题反应的机理通过以下两种方式进行, 其一为2MO+从N2O获取O原子生成2MO2+, 进而向CO提供O原子得到2MO+和CO2, 该过程为催化反应机理; 其二为2MO+先与N2O复合生成中间体IM1, 之后IM1继续与CO复合生成中间体IM2', 经过一系列反应过程最终生成2MO+, N2和CO2. 通过对两种反应过程的热力学性质和动力学因素分析得到, 2MO+(M=Ca, Sr, Ba)参与反应N2O (X1∑+) + CO (X1∑+) → N2 (X1∑+g) + CO2 (X1∑+g)的机理为后一路径, 所得结果与实验观测相符. 相似文献
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本文采用UB3LYP/6-311G(2d) +SDD//CCSD(T)/6-311+ G(2d) +SDD方法,计算研究了气相中碱土金属氧化物阳离子2MO+ (M=Ca,Sr,Ba)参与N2O (X1∑+)+CO(X1∑+)→N2(X1∑g+)+CO2 (X1∑g+)的反应机理.通过计算亲氧性得到在三种氧化物阳离子中只有2CaO+从N2O得到O原子并传递给CO的过程是热力学允许的.碱土金属氧化物阳离子2MO+参与主题反应的机理通过以下两种方式进行,其一为2 MO+从N2O获取O原子生成2MO+,进而向CO提供O原子得到2MO+和CO2,该过程为催化反应机理;其二为2MO+先与N2O复合生成中间体IM1,之后IM1继续与CO复合生成中间体IM2',经过一系列反应过程最终生成2MO+,N2和CO2.通过对两种反应过程的热力学性质和动力学因素分析得到,2 MO+ (M=Ca,Sr,Ba)参与反应N2O(X1∑+)+CO(X1∑+)→N2(X1∑g+)+CO2(X1∑g+)的机理为后一路径,所得结果与实验观测相符. 相似文献
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Electronic structure study for RM12B6 intermetallics (R=Y, La or Ce; M=Fe, Co) was performed. Fixed spin moment calculations for different volumes of unit cell were used to find low and high moment states in LaFe12B6. Obtained results are in agreement with previously obtained experimental and theoretical results. Total magnetic moments obtained for YCo12B6 and LaCo12B6 are in fair agreement with experimental values. In CeCo12B6 discrepancy between theory and experiment seems to be more pronounced. It seems that the calculated Co magnetic moments could be overestimated in the studied RCo12B6 compounds. Present calculations indicate that Fe (Co) atoms prefer 18(h) (18(g)) atomic positions what is in agreement with experiment. 相似文献