NMR determination of the soliton density in incommensurate systems

Blinc, R.; Rutar, V.; Topič, B.; Žumer, S.; Seliger, J.; Aleksandrova, I. P.; Milia, F.

doi:10.1088/0022-3719/19/18/014

Cited by 9 publications

(12 citation statements)

References 30 publications

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“…7,6 In this case, phase difference among nuclear displacements is regarded, but all the distortions are assumed as singleharmonic functions of (x).…”

Section: Pure Nqr Frequency In the Ic Phasementioning

confidence: 99%

“…6 On the other hand, the analysis of the NQR spectra of BCPS performed in all previous works 2-6 lies on the socalled ''local'' model or its improved version, the nonlocal model. 7,8 In these works, the IC modulation was assumed as a plane wave down to 80 K, approximately. Nevertheless, x-ray-diffraction measurements yielded direct experimental evidence of nonsinusoidal atomic modulation functions at 90 K, 9 as it was previously suggested by elastic neutron scattering 10 at temperatures lower than 100 K.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of nuclear-quadrupole-resonance spectrum of incommensurate phases: The case of bis(4-chlorophenyl) sulfone

et al. 1998

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In this work, previous experimental studies of the 35 Cl nuclear-quadrupole-resonance ͑NQR͒ line shape in the incommensurate phase of bis͑4-chlorophenyl͒ sulfone were extended. The broad spectra in the incommensurate phase ͑IC͒ were measured using the Fourier transform of the nuclear signal to avoid systematic errors committed in some studies of this compound. The results were interpreted within the framework of the general treatment developed by Perez-Mato, Walisch, and Petersson. The effects of the incommensurate modulation on the asymmetry parameter of the electric-field gradient were explicitly included in the expression of the NQR frequency. The features of the spectra were adequately reproduced in the whole temperature range, by considering the nonsinusoidal character of the atomic modulations reported by x-ray diffraction. No evidences were found concerning IC wave fluctuations smearing out the singularities of the NQR spectrum. On the other hand, relative intensity of NQR peaks and temperature behavior of some parameters of the plane-wave ''local'' model were explicitly calculated. Comparison of these quantities with the experimental results excludes the applicability of the ''local'' model in the case of bis͑4-chlorophenyl͒ sulfone.

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“…7,6 In this case, phase difference among nuclear displacements is regarded, but all the distortions are assumed as singleharmonic functions of (x).…”

Section: Pure Nqr Frequency In the Ic Phasementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Analysis of nuclear-quadrupole-resonance spectrum of incommensurate phases: The case of bis(4-chlorophenyl) sulfone

et al. 1998

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“…Also shown in figure 4 are our measurements of the misfit parameter δ = 1/pb as a function of temperature. The figure shows firstly that the values of n s deduced by Aramburu et al [26] from their x-ray measurements are considerably different from those obtained from resonance measurements [42]. This is indicative of the difficulty of determining n s when the abrupt-discommensuration model is not adequate.…”

Section: Resonance Measurementsmentioning

confidence: 78%

“…terms in the displacements of the atoms, and because there are a large number of unknown parameters. Initially the interpretation [41] of the data for Rb 2 ZnCl 4 suggested that n s → 0 as T → T L , but a fuller more detailed study [42] of the full line-shape suggested that n s ≈ 0.4 at T L ; the temperature variation is shown in figure 4. Also shown in figure 4 are our measurements of the misfit parameter δ = 1/pb as a function of temperature.…”

Section: Resonance Measurementsmentioning

confidence: 99%

“…It is therefore possible to distinguish between the two models from resonance measurements [14,41]. Unfortunately this is more complex in practice because the resonance frequency may depend on both linear and quadratic [42] (1) and by x-ray scattering by Aramburu et al [26] (2) and of the misfit parameter δ as determined for sample 1 (3).…”

Section: Resonance Measurementsmentioning

confidence: 99%

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The absence of a discommensuration lattice in the incommensurate phase of

Babkevich¹,

Cowley²

1999

J. Phys.: Condens. Matter

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X-ray scattering close to the lock-in temperature has been measured as a function of temperature to investigate whether the discommensuration lattice is a useful description of the structure of . We review different models for the incommensurate structure and discuss how they might be distinguished by a scattering experiment. Our results are compared with earlier published x-ray measurements and with those obtained from nuclear spin-resonance techniques. All of the x-ray results suggest that higher harmonics of the scattering measured in the and planes are much weaker than predicted by the abrupt-discommensuration model. We conclude from the measurements that this theory does not provide an adequate description of the experimental results close to the lock-in transition.

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Exchange dynamics of 23Na and structural incommensuration in NaMo4O6: Dynamic line shape for the second order central transition of quadrupolar nuclei

Chu¹,

Gerstein²

1989

The Journal of Chemical Physics

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Sodium nuclei in NaMo4O exhibit motion as evidenced by the change in asymmetry parameter describing the central transition of 23Na with variable temperature. The nonaxially symmetric electric field gradient observed in the slow motion limit implies that the preferred occupation of the sodium nucleus is not at the center of the tetragonal oxygen cage. At room temperature the sodium jumps randomly within the cage in such a manner as to experience an axially symmetric electric field gradient on average. Dynamic NMR line shape simulations invoking second order broadening of the central transition were performed based on models of four site exchange, and all-site random exchange. Both models yield results indistinguishable from experiment, with an activation energy Ea of 1.95 k cal mol−1. An anomolous upfield shoulder in the central transition is related to the existence of a structural incommensuration. A lower transition temperature Tc=140 K is evidenced by jump discontinuities in both the temperature dependence of T1 and of the quadrupolar coupling constant e2qQ. Using a plane wave approximation to describe the structural incommensuration, the appearance of, and the gradual downfield shift of the upfield shoulder can be satisfactorily fit to the data. From the temperature dependence of the quasicontinuous frequency distribution associated with the incommensurate structure, the upper transition temperature Ti is estimated to be 520 K.

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NMR determination of the soliton density in incommensurate systems

Cited by 9 publications

References 30 publications

Analysis of nuclear-quadrupole-resonance spectrum of incommensurate phases: The case of bis(4-chlorophenyl) sulfone

Analysis of nuclear-quadrupole-resonance spectrum of incommensurate phases: The case of bis(4-chlorophenyl) sulfone

The absence of a discommensuration lattice in the incommensurate phase of

Exchange dynamics of 23Na and structural incommensuration in NaMo4O6: Dynamic line shape for the second order central transition of quadrupolar nuclei

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