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11.
The spinels of the system LixMn1?xV2O4 (0 ? x ? 1) have been prepared at 700–750°C from LiV2O4 and MnV2O4. The lattice constants decrease linearly with increasing x. In the region x>0.75, the d-electrons of V should be delocalized as the VV distances are lower than the critical VV separation of 2.94 Å. Experimentally, the samples with x>0.6 show no IR absorption bands and the Seebeck coefficient is near zero. The Seebeck coefficient can be described with a model of intermediate polarons and can be expressed by the equation . 相似文献
12.
Spinels with substituted Nonmetal Sublattices. IV. CuCr2(S1?xSex)4 and CuCr2(Se1?xTex)4 Polycrystalline samples of the spinel system CuCr2(S1?xSex)4 have been prepared with 0 ≤ x ≤ 1. We found that in the spinel system CuCr2(Se1?xTex)4 no solid solution is existent in the range 0.01 ≤ x ≤ 0.70. When S is substituted by Se and Se by Te the lattice constants increase linearely by 0.52 Å and 0.81 Å respectively. The anion-sublattice shows random distribution of the chalcogen atoms, the chalcogen parameters u are constant in the system CuCr2(S1?xSex)4 with a mean value of u = 0.3829. The calculated anion-cation-distances lead to a covalent tetrahedral radius rCu = 1.23 Å. This radius is in agreement with the radius rCu = 1.22 Å of Cu spinels with Cu in the valence +1. 相似文献
13.
Polycrystalline samples of spinel compounds FeCr2?xInxS4 have been obtained in the range 0 ≦ x ≦ 2. The nonlinear changes of the cell parameters are explained by the nonlinear behavior of the inversion parameter λ according to the ionic distribution Fe2+1?λIn3+λ[Cr3+2?xFe2+λIn3+x?λ]S2?4. Room temperature57Fe-Mo¨ssbauer spectra exhibit two sets of absorptions for tetrahedrally and octahedrally coordinated Fe, respectively, each consisting of several overlapping doublets of similar isomer shifts but varying quadrupole splittings. The partial intensity of octahedral-site Fe is in agreement with λ. The spectra can be understood by accounting for the influence of variable octahedral-site neighbors on tetrahedral-site iron. 相似文献
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16.
G. S. Shakurov R. I. Khaibullin V. G. Tomas D. A. Fursenko R. I. Mashkovtsev O. N. Lopatin A. G. Nikolaev B. P. Gorshunov E. S. Zhukova 《Physics of the Solid State》2017,59(8):1600-1606
Electron spin resonance spectra of non-Kramers bivalent iron (Fe2+) ions have been detected in synthetic and natural beryl crystals with an iron impurity. The observed ESR spectra have been attributed to resonance transitions of Fe2+ ions from the ground (singlet) state to excited (doublet) levels with the splitting Δ = 12.7 cm–1 between the levels. The experimental angular and frequency dependences of the resonance field of the ESR signal have been described by the spin Hamiltonian with the effective spin S = 1. The analysis of the ESR data and optical absorption spectra indicates that the Fe2+ ions are situated in tetrahedral positions and substitute Be2+ cations in the beryl structure. 相似文献
17.
We report a detailed analytic and numerical study of electronic thermal conductivity in d-wave superconductors. We compare theory of the crossover at low temperatures from T dependence to T(3) dependence for increasing temperature with recent experiments on YBa(2)Cu(3)O(7) in zero magnetic field for T approximately [0.04 K,0.4 K] by Hill et al. [Phys. Rev. Lett. 92, 027001 (2004)]. Transport theory, including impurity scattering and inelastic scattering within strong-coupling superconductivity, can consistently fit the temperature dependence of the data in the lower half of the temperature regime. We discuss the conditions under which we expect power-law dependences over wide temperature intervals. 相似文献
18.
J. Riedel S. Hoekstra W. Jäger J. J. Gilijamse S. Y. T. van de Meerakker G. Meijer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,65(1-2):161-166
Here we report on the accumulation of ground-state NH molecules in a static magnetic trap. A pulsed supersonic beam of NH (a1Δ) radicals is produced and brought to a near standstill at the center of a quadrupole magnetic trap using a Stark decelerator. There, optical pumping of the metastable NH radicals to the X3Σ? ground state is performed by driving the spin-forbidden A3Π ← a1Δ transition, followed by spontaneous A → X emission. The resulting population in the various rotational levels of the ground state is monitored via laser induced fluorescence detection. A substantial fraction of the ground-state NH molecules stays confined in the several milliKelvin deep magnetic trap. The loading scheme allows one to increase the phase-space density of trapped molecules by accumulating packets from consecutive deceleration cycles in the trap. In the present experiment, accumulation of six packets is demonstrated to result in an overall increase of only slightly over a factor of two, limited by the trap-loss and reloading rates. 相似文献
19.
H. Preier M. Bleicher W. Riedel H. Pfeiffer H. Maier 《Applied Physics A: Materials Science & Processing》1977,12(3):277-281
PbS−PbSe−PbS double-heterostructure lasers have been pulse-operated at about 200 K mounted on 4 stage thermoelectric coolers.
Emitting at a wavelength of about 5.5 μm they could be used for NO gas spectroscopy. Operation temperatures of up to 230 K
have been achieved with structures consisting ofn-type PbS substrates and epitaxial layers ofn-type PbSe and Tl dopedp-type PbS. The temperature dependence of the threshold current density and the emission wavelength of these DH-lasers was
compared with PbSe-homojunction lasers. The use of a germanium etalon for a quick evaluation of the spectral quality of the
emitted radiation is described. 相似文献
20.
Self-starting mode locking of a Nd:glass fiber laser by use of the third-order nonlinearity of low-temperature-grown GaAs 总被引:5,自引:0,他引:5
Leitner M Glas P Sandrock T Wrage M Apostolopoulos G Riedel A Kostial H Herfort J Friedland KJ Däweritz L 《Optics letters》1999,24(22):1567-1569
We present a diode-pumped Nd:glass fiber laser, emitting at 1060 nm, that is passively mode locked by fast nonlinear loss in low-temperature-grown GaAs (LT-GaAs). This new mode-locking mechanism is based on intensity-dependent defocusing in LT-GaAs that occurs after nonresonant generation of free carriers by two-photon absorption. Mode locking is self-starting and produces pulses as short as 4.1 ps. 相似文献