Amorphous-like acoustical properties of Na doped β-Al2O 3

Doussineau, P.; Frénois, Ch.; Leisure, R. G.; Levelut, A.; Prieur, J.-Y.

doi:10.1051/jphys:0198000410100119300

Cited by 124 publications

(39 citation statements)

References 27 publications

(86 reference statements)

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“…It was however not possible, particularly in the range a>Tmin::::: 1, to get satisfactory results for both internal friction and change of sound velocity with a single set of parameters. On the other hand, similar corrections to the predictions of the tunneling model had been introduced earlier to improve the agreement between internal friction and the resonant contribution to the sound velocity [36][37][38]. There, instead of Eq.…”

Section: Discussionmentioning

confidence: 99%

Low frequency acoustic and dielectric measurements on glasses

et al. 1994

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Abstract. The acoustic and dielectric properties of different glasses at audio frequencies and temperatures below 1 K have been investigated with the vibrating reed and a capacitance bridge technique. We found the temperature dependence of the absorption of vitreous silica (Suprasil W) to agree with the predictions of the tunneling model which is commonly used to explain the low temperature behaviour of amorphous materials. The variation of the sound velocity and of the dielectric constant, however, shows significant deviations from the expected behaviour which cannot be accounted for by a simple modification of the model. Instead, it seems to be necessary to introduce a temperature dependence of some relevant model parameters. Moreover, at very low temperatures (T

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Section: Discussionmentioning

confidence: 99%

Low frequency acoustic and dielectric measurements on glasses

et al. 1994

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“…The general expressions for ␣ and ⌬v/v due to this process are given in Ref. 11 and can be calculated numerically. Analytic solutions can be derived for the limiting cases m ӷ1 ͑lowest temperatures͒ and m Ӷ1 ͑higher temperatures͒, with m the smallest relaxation time of the TS.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

“…At higher temperatures, above a few Kelvin, a two-phonon Raman process has to be taken into account. 11 A modified relaxation time has to be introduced: Ϫ1 ϭ d Ϫ1 ϩ r Ϫ1 in which d is the relaxation time for the one-phonon processes ͓see Eq. ͑2͔͒ and r the relaxation time for the Raman processes.…”

Section: Theoretical Considerationsmentioning

confidence: 99%

Tunneling states in vitreousGeO2s

Laermans¹,

Keppens²,

Weeks³

1997

Phys. Rev. B

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Ultrasonic measurements of the attenuation and the velocity variation have been carried out in amorphous GeO 2 at low temperature ͑0.3-10 K͒ and high frequencies ͑80-210 MHz͒. From numerical fits to the tunneling model, the typical parameters of the tunneling states ͑TS͒ were determined and compared to those found for vitreous SiO 2 . The study reveals that in a-GeO 2 , which is considered as a close structural analog to a-SiO 2 , although the density of states is found to be very similar in both materials, the coupling between the TS and the phonons is significantly smaller. In the model of coupled tetrahedra as the origin of the TS, this difference can be understood in view of the fact that numerical calculations about the vibrational characteristics of network amorphous solids indicate that the tetrahedra are more decoupled in vitreous GeO 2 than in vitreous silica.

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“…At higher temperatures, above a few Kelvin, the Raman processes need to be taken into account. 13 A modified relaxation time has to be introduced: Ϫ1 ϭ d Ϫ1 ϩ r Ϫ1 in which d is the relaxation time for the one-phonon processes and r the relaxation time for the Raman process. This additional process causes a stronger temperature dependence in the transition region from the m ӷ1 to the m Ӷ1 regime.…”

Section: ͑8͒mentioning

confidence: 99%

Influence of heat treatment on the tunneling states in neutron-irradiated quartz

Keppens

Laermans

1996

Phys. Rev. B

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We report the results of a systematic study of the influence of heat treatment on the tunneling states ͑TS͒ in neutron-irradiated quartz. Measurements of the ultrasonic attenuation and velocity change are carried out before and after heat treatment, as a function of temperature ͑0.3-300 K͒ and in the ultrasonic frequency range ͑50-650 MHz͒, on well-characterized specimens. Two doses have been studied, irradiated, and heat treated under similar conditions. One dose is lying well below the so-called threshold dose, the other is situated near the threshold. From numerical fits of the data with the tunneling model, the density of states P and the coupling parameter ␥ l were determined independently. This allows us to investigate the influence of the heat treatments on the number and nature of the TS. Attention is paid to both the influence of the annealing temperature and the length of the heat treatment. All samples still show the typical TS behavior after heat treatment, but the density of states is drastically reduced. Regarding the coupling, the two doses show a different behavior: while there is no influence on the coupling for the higher dose, a significant decrease in ␥ l is observed for the lowest dose. This decrease can be interpreted in terms of changes in the tunneling entity itself and is in agreement with the changes in the distribution of the TS.

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Amorphous-like acoustical properties of Na doped β-Al2O 3

Cited by 124 publications

References 27 publications

Low frequency acoustic and dielectric measurements on glasses

Low frequency acoustic and dielectric measurements on glasses

Tunneling states in vitreousGeO2s

Influence of heat treatment on the tunneling states in neutron-irradiated quartz

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