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1.
The theories of Kyame [1] and Koga et al. [2] on stress wave propagation in piezoelectric media are critically studied and compared with each other. Solutions of the modified Christoffel's equations predicted by each theory for piezoelectric crystals in class 3m are derived. The velocities of ultrasonic waves propagated through a gem quality uvite specimen in particular directions were measured at 293 K using the pulse-echo overlap method. All of the independent zero-field elastic moduli were calculated from the measured wave velocities and compared with the available data in the literature. The values of the elastic constants in 1012dyncm2 were found to be C11 = 3.016 ± 0.2% C66 = 1.028 ± 0.3% C33 = 1.698 ± 0.2% C13 = 0.47 ± 3% C44 = 0.655 ± 0.3% c14 = ?0.089 ± 6%. The calculated bulk modulus, shear modulus and Poisson's ratio, using the Voigt-Reuss-Hill (VRH) approximation, are KH = 1.226 × 1012dyncm2, GH = 0.826 × 1012dyncm2 and σH = 0.224. The Debye temperature is 764 K.  相似文献   

2.
The surface self-diffusion coefficients, Ds, on a Ni(110) crystal are measured by a mass transfer technique in [110] and [001] directions in the temperature range 773–1573 K. The surface cleanliness was checked by Auger electron spectroscopy. LEED investigations showed that the sinusoidal surface profile consisted of (110) terraces and monatomic steps. The temperature dependence of Ds can be expressed by Ds [110] = 0.009 exp(?17.5 kcalmole · RT) and Ds [001] = 470 exp(?45 kcalmole · RT) at temperatures below 1150 K. Theoretical values for the activation energies of surface migration were calculated in the framework of the pairwise interaction model. Together with an estimate for the formation energy of adatoms of 16.3 kcalmole, one obtains for the activation energy of surface self-diffusion 17 and 51 kcalmole for [110] and [001] direction, respectively. At T > 1150 K the anisotropy in Ds begins to vanish. Surface diffusion in [110] direction at T < 1150 K is most likely taking place by a simple adatom hopping process. Circumstantial evidence indicates that diffusion in [001] direction does not occur by a simple hopping process but by a more complex mechanism involving higher energy surface diffusion states. This isotropic process is suggested to take place for both directions at T < 1150 K.  相似文献   

3.
The exact theory for the frequency of transition between the two lowest levels of a spin I = 32 nucleus experiencing a large asymmetric electric field gradient, an applied magnetic field, and an anistropic chemical interaction was presented in an earlier paper. Using the assumption that the quadrupolar and chemical shift tensors have the same principal axis system, the Hamiltonian was solved exactly — analytically for the applied field aligned along each of the three axes of the quadrupolar principal axis system, and numerically for arbitrary orientations.This theory is reviewed here and applied to our room-temperature experiments in single-crystal paradibromobenzene. The self-consistent least-squares fit to the field-dependencies and simultaneously the angular dependence (rotational pattern) of the resonance frequency was performed using the literature value for the pure quadrupole frequency νQ(1 + η23)12 = 223·8 MHz. The fit yielded values for the quadrupolar asymmetry η = 0·0461 ± 0·0004 and the chemical shift components σx = ?0·001 ± 0·001, σv = σz = 0·000 ± 0·001. Our value for η is in good agreement with values determined by other methods; it and our shift values are consistent with the information obtained by this method using a powdered specimen.The process of using the NMR signal itself to align the specimen yielded sufficient information for an unambiguous determination of the Euler angles of orientation of the crystal in its mounting within ± 0.6°.  相似文献   

4.
5.
A small polycrystalline ingot sample of NpCo2Si2 (weight ≈ 1.5 g) has been studied by neutron diffration between 2 and 160 K on the multi-detector D1B of ILL, Grenoble. At 100 K, the crystal structure is body-centered tetragonal (space group 14/mmm) with a = 3.886 Å and c =9.649 Å. Below TN = (44 ± 2) K, seven superlattice lines are observed which correspond to a simple tetragonal lattice with lattice constants as above. They are consistent with a type I antiferromagnetic structure of the Np (2a) sublattice, with (001) ferromagnetic sheets coupled antiferromagnetically according to the sequence +-+-. At 6 K, the neptunium moment obtained from the diffracted intensities is: (1.48 ± 0.20)μuB, and makes an angle 52° ± 15° with the c axis. The cobalt moment is certainly smallet than 0.3μuB. The Np moment correlates well with the 237Np hyperfine field deduced from Mos?sbauer spectroscopy; the sublattice magnetization-temoperature curve follows very well the J=12 brillouin curve. The magnetism is therefore probably of lovalized character in this compound. An isomorphous sample of NpCu2Si2 (a = 3.990 Å c = 9.920 Å) was shown to be ferromagnetic below (41 ± 2) K, with the Np moment [1.5 ± 0.2)μuB] aligned along the c axis.  相似文献   

6.
The magnetic ordering in uranium monophosphide (UP) has been studied by neutron diffraction from a single crystal in a magnetic field. UP orders at TN ? 122 ± 0.1 K with the type-I antiferromagnetic structure (+-+-), the ordering taking place in a first-order transition. At T0 = 22.5 K the ordered magnetic moment jumps from 1.7 μB to 1.9 μB. With a magnetic field H = 25 kOe applied along the [11&#x0304;10] direction, it is found that UP has the collinear single-K type-I structure above T0 and undergoes a first-order transition to the planar double-K type-I structure, accompanied by a “moment jump” due to the change in the moment direction from <001> to <110>.  相似文献   

7.
Magnetoreflectance measurements on the Γ6 ? Γ8 free exciton ground state in cubic ZnSe in magnetic fields up to 18 Tesla are reported. The diamagnetic shift rate of the ground state components: |32, |?32, |12 and |?12 yield γ2 = 0.53 ± 0.07 and an exciton reduced mass μ0 = 0.117 ± 0.003, corresponding to γ1 = 2.30 ± 0.45 for me1 = 0.16 m0. γ1, γ2 and an effective hole g-value κtilde = -0.21 yield γ3 = 0.82 ± 0.16 in the parabolic approximation and in agreement with the observed splitting of the |?32, |?12 states for B ∥ [110]. Taking into account polaron effects we derive bare valence band parameters γ1L = 2.71 ± 0.60, γ2L = 0.63 ± 0.09 and γ3L = 0.97 ± 0.21 from the renormalized parameters γi. The present results are considerably smaller than earlier theoretical calculations suggest, however they are in good agreement with a recent detailed analysis of two-photon absorption data for 2P exciton states.  相似文献   

8.
Reflectance spectra were measured on ZnTe in magnetic fields up to 18 T for B ? [100] and B ? [110]. The experiments yield renormalized valence band parameters γ12 = 0.83 ± 0.08 and γ13 = 1.30 ± 0.12, corresponding to bare parameters γ2 = 0.95 ± 0.09 and γ3 = 1.48 ± 0.14. From the free exciton Rydberg energy R10 = 12.8 meV we derive a reduced exciton polaron mass m0 0.080 ± 0.005 and a bare reduced mass m0 0.074 ± 0.005, corresponding to γ11 = 3.9 ± 0.7 and γ1 = 4.4 ± 0.7 for an electron effective polaron mass m1e = 0.116 m0. We further calculate the exciton diamagnetic shift rate according to existing low-field theories modified by a variational calculation taking into account polaron effects and valid up to γ ? 1. The difference between experiment and theory is 10% and the agreement is considered satisfactory.  相似文献   

9.
Using X-ray diffraction the compression of cubic ZnS (sphalerite) has been measured to 9.4 GPa under hydrostatic pressure conditions. The results analysed using a two parameter Birch-Murnaghan equation may be presented by K0 = 74.8 ± 3.2 GPa and K0 = 4.91 ± 1.2. These compare well with 3.76 ± 0.96 for K0 = 76.5 GPa, the value calculated by Chang and Barsch from their wurzite data. Δaao, the change in lattice parameter at 15 GPa in ZnS is 0.255A? ± 0.012 corresponding to a change of 0.110 A? ± 0.005 in Zn-S distances at this transition to the metallic state.  相似文献   

10.
The microwave spectra of 2-fluorophenol and its deuterated species have been observed and analyzed in the frequency ranges 12.5–18.0 GHz (KU band) and 21.5–26.0 GHz (K band) in the ground vibrational state at room temperature. For the normal species, the radio frequency-microwave double resonance spectrum has been recorded in the frequency range 30.0–38.0 GHz. Three rotational and five quartic centrifugal distortion constants for the normal species, A? = 3337.86 ± 0.02, B? = 2231.92 ± 0.01, C? = 1337.52 ± 0.01, dJ = (3.5 ± 2.9) × 10?4, dJK = (?4.9 ± 1.5) × 10?3, dK = (?3.2 ± 1.0) × 10?3, dWJ = (?2.0 ± 1.0) × 10?7, dWK = (2.6 ± 0.8) × 10?6 (in MHz), and three rotational constants for the deuterated species, A? = 3324.70 ± 0.03, B? = 2177.95 ± 0.03, C? = 1315.96 ± 0.03 (in MHz), have been obtained. Consideration of the rs coordinate of the hydroxyl hydrogen atom leads to the assignment of the spectra to the cis conformer of the molecule. An r0 structure for the cis conformer has been proposed. The nonbonded OH ? F distance is lower by about 0.3 Å than the sum of the van der Waals radii.  相似文献   

11.
Gold-doped silver chloride annealed in a chlorine atmosphere at 300°C is shown to contain precipitates of AgAuCl4, a compound not previously reported. The substance melts at 265 ± 2°C and has a monoclinic unit cell with a = 11.124 ± 0.008A?, b = 4.105 ± 0.002A?, c = 6.539 ± 0.006A? and β = 93.11 ± 0.05°. Its optical absorption spectrum is discussed and the method of precipitate formation in silver chloride is described in terms of an internal oxidation type of process.  相似文献   

12.
The microwave spectrum of dimethyldichlorosilane has been observed and the rotational constants and centrifugal distortion constants have been determined for 35Cl2 and 35Cl37Cl species. From these constants, the molecular structure is determined as r(SiCl) = 2.055 ± 0.003 A?, r(SiC) = 1.845 ± 0.005 A?, ∠ClSiCl = 107.2 ± 0.3°, ∠CSiC = 114.7 ± 0.3°. An analysis of the 35Cl2 quadrupole splittings leads to quadrupole coupling constants of χaa = ?19.6 ± 0.3 MHz, χbb = ?3.7 ± 1.4 MHz, χcc = 23.3 ± 1.4 MHz, χbond = ?38.0 ± 1.6 MHz, and ηbond = 0.22 ± 0.08.  相似文献   

13.
The nuclear g-factor of the 4498 keV 172+ isomeric state in 63Cu was measured with the in-bearn perturbed angular distribution method, through the 62Ni(α, p2nγ)63Cu reaction, to be gexp = 0.184 ± 0.012. This value is in good agreement with a semiempirical g-factor for the three-quasiparticle configuration [π2p32(v1f52, 1g92)7]172+ calculated using the experimental single-particle g-factors of neighbouring nuclei. At the same time the internal magnetic field at the Cu nuclei in Ni metal was obtained to be Bint = ?46.6 ± 1.3 kG.  相似文献   

14.
The EPR spectra of thermally treated BaF2: Mn samples is reported. After thermal annealing at 900 K a trigonal Mn2+ center with g=2.000±0.005, |D|=2725±40MHz, |A|=265±10MHz, DA>0, is observed. Annealing at 1200 K produces an orthorhombic Mn2+ center with g=2.00±0.01, |D|=2430±40MHz, |E|=570±20MHz, |A|=265±10MHz, DA<0. The superhyperfine (SHF) structures due to interactions with the neighbouring fluorines indicates that the trigonal manganese interacts with four fluorines, three of them equivalent. The orthorhombic Mn2+ shows interaction with four equivalent fluorine nuclei.  相似文献   

15.
The propagation of the surface acoustic mode in the (001) plane is investigated as a function of the temperature dependent elastic moduli of Nb3Sn in the cubic phase. For the [100] and [110]-directions a softening of the surface mode velocity νs is found to follow the softening of the velocity νT2 of the bulk shear mode T2A. It is shown that for the [100]-direction the ratio (νsνT2) tends to ?2 at the structural phase transition. The question is discussed of whether the softening of the surface mode can be observed with Brillouin scattering from opaque surfaces.  相似文献   

16.
Elastic low energy electron diffraction (LEED) intensity-energy (I-E) measurements for clean (001), (110), and (111) nickel surfaces were obtained at room temperature. Surface composition was monitored by Auger spectroscopy. I-E data from 15 to 220 eV were obtained at normal incidence for the non specular beams and for the specular beams at incidence angles from 4° to 20° on the 0° and 45° azimuths of (001), on the 0° and 90° azimuths of (110), and on the 0° azimuth of (111) nickel. Normalization of the data was performed electronically during data acquisition. Intensities were calibrated with the use of a shielded, biased Faraday collector. The effects of instrumental and experimental uncertainties were examined and minimized to obtain intensities accurate to ± 15 %, energy scales accurate to ± 0.35 eV, and incident and azimuthal angles accurate to ± 0.25° and ± 1.0° respectively.All nickel surfaces have I-E spectra which are characteristic of strong multiple scattering. Angular evolution features for (001) and (110) spectra may be correlated with intraplanar resonances associated with the onset of propagating beams. Only the (001) surfaces were found to have pronounced, sharp resonance features associated with surface barrier resonances and inelastic loss processes. Kinematic analysis of the Lorenzian-shaped I-E peaks on all surfaces in consistent with surface expansion using either an energy-dependent or a constant inner potential of 10.75 ± 0.5 eV. The widths of these same peaks on all surfaces were found to vary as E12 above 40 eV and E13 below.  相似文献   

17.
The microwave spectra of ethaneselenol and its deuterated and 13C-substituted species were measured and assigned for the gauche and trans isomers. The double minimum splittings in the gauche isomers were directly observed for the species having a symmetry plane in the frame part. The rotational constants and the torsional splitting of the gauche isomer of the parent species were determined to be A = 27 148.86 ± 0.05, B = 3 623.68 ± 0.01, C = 3 399.21 ± 0.03, and Δν = 1 083.33 ± 0.04 MHz. From the torsional splittings of the parent and SeD species together with the vibrational frequencies already reported by Durig and Bucy, the Fourier coefficients of the selenol internal rotation potential function were determined to be V1 = ?44 ± 17, V2 = ?260 ± 3, V3 = 1202 ± 16, and V6 = ?43 ± 9 cal/mole. From the rotational constants obtained, the rs structural parameters of the gauche and trans isomers were determined. The structural parameters in the skeletal part for the gauche isomer are r(CC) = 1.524 A?, r(CSe) = 1.957 A?, r(SeH) = 1.467 A?, α(CCSe) = 113°31′, α(CSeH) = 93°05′, and the dihedral angle τ(CCSeH) = 61°39′. Those for the trans isomer are r(CC) = 1.525 A?, r(CSe) = 1.962 A?, r(SeH) = 1.440 A?, α(CCSe) = 108°43′, and α(CSeH) = 93°30′. These parameters were compared with the corresponding ones of ethanethiol.  相似文献   

18.
The lowest four T = 32 levels of 17O have been observed as resonances in the 13C(α, n)16O reaction. Excitation energies and widths obtained for these levels are 11.076 ± 0.005 MeV, Γc.m. = 5.0 ± 1.1 keV; 12.458 ± 0.005 MeV, Γc.m. = 8 ± 2 keV; 12.944 ± 0.006 MeV, Γc.m. = 6 ± 2 keV; 12.993 ± 0.006 MeV, Γc.m. < 3 keV. The total and partial decay widths for the lowest T = 32 level are much larger than those of the analogue level in 17F, implying significant isotensor components in the T = 12 admixtures.  相似文献   

19.
The hadronic part aH of the muon g-factor anomaly a ≡ (g ? 2)2 is evaluated from latest data on σ(e+e? → hadrons). For a p-wave ππ scattering length of a1 = 0.04±0.005 we calculate aH = (66±10) × 10?9, compared to a(experiment) ? a(QED) = (60±29) × 10?9. Half of the uncertainty on aH is associated with the energy interval 0.92 < s < 2 GeV.  相似文献   

20.
The ν4 infrared and Raman bands of CH3Cl were analyzed simultaneously. A direct fit yielded a complete set of constants for CH335Cl, including A0 = 5.20530 ± 0.00010 cm?1 and DK = (8.85 ± 0.13) × 10?5cm?1. For CH337Cl an incomplete set of constants was obtained from the infrared band, and A0 = 5.2182 ± 0.0010 cm?1 was estimated by curve fitting of the Raman spectrum. The resulting equilibrium structure is r(CH) = 1.0854 ± 0.0005 A?, r(CCl) = 1.7760 ± 0.0003 A?, and <(HCH) = 110°.35 ± 0°.05.  相似文献   

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