Ultrasonic Velocity and Attenuation in Alkali Halides Containing CN<sup>−</sup> I. Experimental Results

Byer, N. E.; Sack, H. S.

doi:10.1002/pssb.19680300218

Cited by 36 publications

(4 citation statements)

References 7 publications

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“…For various defects it is possible t o align the elastic dipoles by uniaxial stress almost completely a t low temperature. This alignment has been monitored by different methods, for example by measurements of the dichroism of the UV-or IR-bands [l to 41 or by ultrasonic methods [5]. Successful candidates in the search of paraelastic centres have been off-centre defects [ S ] and small molecular ions like OH-, CN-, and NHF [l to 41, since these centres provide sufficient reorientations1 rates at low temperatures.…”

Section: Introductionmentioning

confidence: 99%

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH⁻ Centres in CsBr

Otto

1988

Physica Status Solidi (b)

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Paraelastic alignment of SH-centres in CsBr leads t o a stress-induced dichroism of the infrared absorption lines and their phonon sidebands. The principal values of the elastic dipole tensor are determined from quantitative infrared measurements under uniaxial stress. The centres turn out t o be (l00) oriented and have a disk-shaped elastic dipole tensor.The stress-alignment is used to determine the polarization of t h e phonon sidebands with respect to the molecular axis. Those irreducible representations, by which phonons and localized modes mainly couple to the intramolecular vibration, are derived with the help of group-theoretical considerations. Selection rules for the appearance of part,icular phonons in the sidebands are discussed.Paraelastische Ausrichtung von SH--Zentren in CsBr fuhrt zu einem druckinduzierten Dichroismus der IR-Absorptionslinien und deren Phononenseitenbanden. Die Eigenwerte des elastischen Dipoltensors werden aus quantitativen IR-Messungen unter einachsigem Druck bestimmt. Es zeigt sich, daD die Zentren

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Section: Introductionmentioning

confidence: 99%

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH⁻ Centres in CsBr

Otto

1988

Physica Status Solidi (b)

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“…Yet the multiexponential decay with the two rates 1 and 2 gives rise to quite an intricate relaxation spectrum; thus an experimental investigation of the frequency dependence would seem most promising. Simliar behaviour was also found for an E g -mode [9] contradicting the simplest model of an [111]-defect. Even asymmetries cannot explain this feature in a simple way.…”

Section: Comparison Of Theory and Experimentsmentioning

confidence: 82%

“…Early measurements in KCl:CN samples [9] in the classical regime (k B T ) showed that the change of sound velocity of a T 2g -mode (ê = [110],k = [001]) varies as expected similiar to 1/T with temperature. Yet in addition, these experiments showed a change of sound velocity for an E g -mode (ê = [110],k = [110]) with an amplitude of about ten times smaller than the T 2g ones, whereas this mode should be unaffected according to the simplest model of a symmetric [111]-tunnelling defect.…”

Section: Introductionmentioning

confidence: 95%

Progress and prospect of laser thermonuclear fusion

Basov¹

1993

Quantum Electron.

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We study the dynamic response of a [111] quantum impurity, such as lithium or cyanide in alkali halides, with respect to an external field coupling to the elastic quadrupole moment. Because of the particular level structure of a eightstate system on a cubic site, the elastic response function shows a biexponential relaxation feature and a van Vleck type contribution with a resonance frequency that is twice the tunnel frequency /h. This basically differs from the dielectric response that does not show relaxation. Moreover, we show that the elastic response of a [111]-impurity cannot be reduced to that of a two-level system. In the experimental part, we report on recent sound velocity and internal friction measurements on KCl doped with cyanide at various concentrations. At low doping (45 ppm) we find the dynamics of a single [111]-impurity, whereas at higher concentrations (4700 ppm) the elastic response indicates rather strongly correlated defects. Our theoretical model provides a good description of the temperature dependence of δv/v and Q −1 at low doping, in particular the relaxation peaks, the absolute values of the amplitude and the resonant contributions. From our fits we obtain the value of the elastic deformation potential γ t = 0.192 eV.

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“…Early measurements in KCl:CN samples [9] in the classical regime (k B T ) showed that the change of sound velocity of a T 2g -mode ( ê = [110], k = [001]) varies as expected similiar to 1/T with temperature. Yet in addition, these experiments showed a change of sound velocity for an E g -mode ( ê = [110], k = [1 10]) with an amplitude of about ten times smaller than the T 2g ones, whereas this mode should be unaffected according to the simplest model of a symmetric [111]-tunnelling defect.…”

Section: T 1u T 2gmentioning

confidence: 95%

Elastic response of [111]-tunnelling impurities

Nalbach

Terzidis

Topp

et al. 2001

J. Phys.: Condens. Matter

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We study the dynamic response of a [111] quantum impurity, such as lithium or cyanide in alkali halides, with respect to an external field coupling to the elastic quadrupole moment. Because of the particular level structure of a eight-state system on a cubic site, the elastic response function shows a biexponential relaxation feature and a van Vleck type contribution with a resonance frequency that is twice the tunnel frequency Δ/ℏ. This basically differs from the dielectric response that does not show relaxation. Moreover, we show that the elastic response of a [111]-impurity cannot be reduced to that of a two-level system. In the experimental part, we report on recent sound velocity and internal friction measurements on KCl doped with cyanide at various concentrations. At low doping (45 ppm) we find the dynamics of a single [111]-impurity, whereas at higher concentrations (4700 ppm) the elastic response indicates rather strongly correlated defects. Our theoretical model provides a good description of the temperature dependence of δv/v and Q-1 at low doping, in particular the relaxation peaks, the absolute values of the amplitude and the resonant contributions. From our fits we obtain the value of the elastic deformation potential γt = 0.192 eV.

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Ultrasonic Velocity and Attenuation in Alkali Halides Containing CN⁻ I. Experimental Results

Cited by 36 publications

References 7 publications

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH⁻ Centres in CsBr

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH⁻ Centres in CsBr

Progress and prospect of laser thermonuclear fusion

Elastic response of [111]-tunnelling impurities

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Ultrasonic Velocity and Attenuation in Alkali Halides Containing CN− I. Experimental Results

Cited by 36 publications

References 7 publications

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH− Centres in CsBr

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH− Centres in CsBr

Progress and prospect of laser thermonuclear fusion

Elastic response of [111]-tunnelling impurities

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Resources

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Ultrasonic Velocity and Attenuation in Alkali Halides Containing CN⁻ I. Experimental Results

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH⁻ Centres in CsBr

Stress‐Induced Dichroism of the Vibrational Lines and Phonon Sidebands of SH⁻ Centres in CsBr