| Issue |
J. Phys. Colloques
Volume 42, Number C6, Décembre 1981
International Conference on Phonon Physics
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|---|---|---|
| Page(s) | C6-33 - C6-33 | |
| DOI | https://doi.org/10.1051/jphyscol:1981608 | |
J. Phys. Colloques 42 (1981) C6-33-C6-33
DOI: 10.1051/jphyscol:1981608
LOW-TEMPERATURE ACOUSTICAL PROPERTIES OF Na DOPED β-Al2O3
J.-Y. Prieur1, P. Doussineau1, C. Frenois1, A. Levelut1 et R.G. Leisure21 Laboratoire d'Ultrasons, Université Pierre et Marie Curie, Tour 13, 4 place Jussieu, 75230 Paris Cedex 05, France
2 Department of Physics, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
Abstract
We measured the attenuation and velocity variations of ultrasonic waves, propagating parallel to the conduction plans in a Sodium doped β Alumina crystal. The three pure modes have been used. The results are well explained in the framework of the "two level system" (TLS) theory developed for amorphous compounds for all the temperature range studied (T < 70 K). In the lowest range of temperature we observed the logarithmic variation of the velocity (T < 5 K). Then for 15 < T < 70 K, we observed a linear variation of the velocity and a plateau for the attenuation variation, the height of which increases as the first power of the frequency. We clearly identified this plateau with the one which was theoretically predicted for the part of the sound attenuation due to the relaxation of the TLS and which is a direct proof of the distribution of the coupling constant for TLS of given energy. However we show that the relaxation of the TLS involved the direct process for T < 10 K and the Raman process for T > 15 K. The consideration of the Raman process and of the elastic anharmonicity let us explain the velocity variations in all the temperature range studied. [1]