Low temperature specific heat of annealed high-purity niobium in magnetic fields

Silva, J.Ferreira da; Burgemeister, E.A.; Dokoupil, Z.

doi:10.1016/0031-8914(69)90046-9

Cited by 55 publications

(6 citation statements)

References 48 publications

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“…69 It has also been applied to the collision induced dissociation of niobium cluster ions by Armentrout and co-workers. 24 They used a Debye frequency for niobium of 1200 cm ;-I which implies a Debye temperature of 1700 K, whereas low temperature specific heat data imply a Debye temperature of250 K. 71 We have used the latter value.…”

Section: Appendixmentioning

confidence: 99%

Multiphoton excitation, ionization, and dissociation decay dynamics of small clusters of niobium, tantalum, and tungsten: Time-resolved thermionic emission

Amrein

Simpson

Hackett

1991

The Journal of Chemical Physics

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Articles you may be interested inCommunication: IR spectroscopy of neutral transition metal clusters through thermionic emission Selection of the substrate metal best for thermal positive ionization Rev. Sci. Instrum. 71, 856 (2000)Magic numbers in transition metal (Fe, Ti, Zr, Nb, and Ta) clusters observed by time-of-flight mass spectrometry J. Chem. Phys. 111, 235 (1999); 10.1063/1.479268 Thermionic electron emission of small tungsten cluster anions on the milliseconds time scaleThe ionization dynamics of transition metal clusters have been investigated using time-of-flight mass and electron spectroscopy following single-photon (220 nm) and two-photon (351,308, and 248 nm) excitation by pulsed laser light. At 220 nm, the ionization is direct and only prompt photoelectrons are produced. At 308 nm, delayed photoelectrons are produced. In consequence of this delayed ionization process, the time-of-flight mass spectrum peaks show exponential tails (decay time 0.67, 0.40, and 1.54 J-ls for Nb/ , Ta/ , and W / , respectively). The decay time is shown to have an explicit dependence upon the cluster nuclearity and the laser wavelength. Experiments, in which the acceleration voltage of the time-of-flight spectrometer is pulsed on after the photoionization laser pulse, reveal that the precursor to the delayed ion signals is a neutral molecule, further evidence for a delayed ionization process. Similar effects are also seen for transition metal carbide clusters. Clusters of the same nuclearity have approximately equal decay times independent of the number of carbon atoms in the cluster. Transition metal oxide clusters do not give a two-photon ionization signal. These observations are explained using a model for the two-photon excitation, dissociation, and ionization dynamics. The central feature of this model is that following single photon excitation of an electronic transition below the ionization potential, there is rapid internal conversion among all vibronic states. The absorption of a second photon then creates a vibrationally excited cluster which contains internal energy greater than the ionization potential, but which can only ionize by a nonadiabatic process. This delayed ionization process occurs in competition with dissociation. As clusters of niobium, tantalum, and tungsten and their carbides are very strongly bound, the dissociation rate is slow and the delayed ionization may be observed. Oxidized clusters are expected to be less strongly bound as the diatomic transition metal oxide provides an excellent leaving group; in consequence, no delayed ionization is observed for partially oxidized clusters. The rates for dissociation and ionization of the bare metal clusters have been calculated within the framework of a generalized statistical theory for cluster processes. These rates are in general agreement with the measured decay times. In addition, the rates have been estimated by a procedure which uses tabulated thermodynamic parameters for the bulk elemental materials and makes an explicit correction for the...

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Section: Appendixmentioning

confidence: 99%

Multiphoton excitation, ionization, and dissociation decay dynamics of small clusters of niobium, tantalum, and tungsten: Time-resolved thermionic emission

Amrein

Simpson

Hackett

1991

The Journal of Chemical Physics

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“…For the following comparison of the maximum RF field with theory the value of T c =9.11 K derived from the pulsed measurement will be used. Figure 4 shows the maximum RF field normalized to the thermodynamic critical field B c =199 mT 18,19 as a function of temperature. Here it can be seen that the maximum RF field systematically exceeds B c .…”

Section: Maximum Rf Fieldmentioning

confidence: 99%

“…Figure 4 shows the maximum RF field normalized to the thermodynamic critical field B c =199 mT 18,19 as a function of temperature. Here it can be seen that the maximum RF field systematically exceeds B c .…”

Section: Maximum Rf Fieldmentioning

confidence: 99%

Extension of the measurement capabilities of the quadrupole resonator

Junginger

Weingarten

Welsch

2012

Review of Scientific Instruments

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The Quadrupole Resonator, designed to measure the surface resistance of superconducting samples at 400 MHz has been refurbished. The accuracy of its RF-DC compensation measurement technique is tested by an independent method. It is shown that the device enables also measurements at 800 and 1200 MHz and is capable to probe the critical RF magnetic field. The electric and magnetic field configuration of the Quadrupole Resonator are dependent on the excited mode. It is shown how this can be used to distinguish between electric and magnetic losses.

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“…Varieties of materials exhibit this βγ-change: examples include group V transition metals V, Nb and Ta (Fig. 1) [2][3][4][5] the Chevrel phases PbMo 6 X 8 (X=S, Se), 6,7 the A12-type Re 3 W, 8 the A15-type Nb 3 Sn and V 3 Si (Fig. 2), 9,10 the layered NbSe 2 , 11 the perovskite MgCNi 3 (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…In spite of this back- FIG. 1: C/T versus T 2 curves of (a) V, 5 (b) Nb (H = 1.15 T ), 4,5 (c) Ta. 5 .…”

Section: Introductionmentioning

confidence: 99%

On the anomalous thermal evolution of the low-temperature, normal-state specific heat of various nonmagnetic intermetallic compounds

ElMassalami¹

2011

Preprint

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The low-temperature normal-state specific heat and resistivity curves of various nonmagnetic intermetallic compounds manifest an anomalous thermal evolution. Such an anomaly is exhibited as a break in the slope of the linearized C/T versus T 2 curve and as a drop in the R versus T curve, both at the same T βγ . It is related, not to a thermodynamic phase transition, but to a Kohn-type anomaly in the density of states curves of the phonon or electron subsystems. On representing these two anomalies as additional Dirac-type delta functions, situated respectively at kBθL and kBθE, an analytical expression for the total specific heat can be obtained. A least-square fit of this expression to experimental specific heat curves of various compounds reproduced satisfactorily all the features of the anomalous thermal evolution. The obtained fit parameters (in particular the Sommerfeld constant γ0 and Debye temperatures θD) compare favorably with the reported values. Furthermore, the analysis shows that (i) T βγ /θL = 0.2 1 ± 1/ √ 6 and (ii) γ0 ∝ θ −2 D ; both relations are in reasonable agreement with the experiments. Finally, our analysis (based on the above arguments) justifies the often-used analysis that treats the above anomaly in terms of either a thermal variation of θD or an additional Einstein mode.

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Low temperature specific heat of annealed high-purity niobium in magnetic fields

Cited by 55 publications

References 48 publications

Multiphoton excitation, ionization, and dissociation decay dynamics of small clusters of niobium, tantalum, and tungsten: Time-resolved thermionic emission

Multiphoton excitation, ionization, and dissociation decay dynamics of small clusters of niobium, tantalum, and tungsten: Time-resolved thermionic emission

Extension of the measurement capabilities of the quadrupole resonator

On the anomalous thermal evolution of the low-temperature, normal-state specific heat of various nonmagnetic intermetallic compounds

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