LOW-TEMPERATURE ACOUSTICAL PROPERTIES OF Na DOPED β-Al2O3

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LOW-TEMPERATURE ACOUSTICAL PROPERTIES

OF Na DOPED β-Al2O3

J.-Y. Prieur, P. Doussineau, C. Frenois, A. Levelut, R. Leisure

To cite this version:

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JOURNAL DE PHYSIQUE

CoZZoque C6, suppZhent au n012, Tome 42, de'cembre 2981 page C6-33

LOW-TEMPERATURE A C O U S T I C A L P R O P E R T I E S OF N a DOPED 6.-A1203

J.-Y. Prieur, P. Doussineau, C. Frenois, A. Levelut and R.G. ~eisure*

Laboratoire d'UZtrasons, UniversitQ Pierre e t Marie Curie, Tour 23, 4 p k c e Jussieu, 75230 Paris Cedex 05, France

" ~ e p a r t m e n t o f Physics, CoZorado S t a t e University, Fort CoZZins, Co Zorado 80523, U. S. A.

Abstract.

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We measured the attenuation and velocity variations of ultrasonic waves, propagating parallel to the conduction plans in a Sodium doped 8 Alumi- na crystal. The three pure modes have been used. The results are well explain- ed 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 < 10K

and the Raman process for T > 15 K. The consideraction of the Raman process and of the elastic anharmonicity let us explain the velocity variations in all the temperature range studied. [ I ]

[ I ] Amorphous-like acoustical properties of Na doped B-Al20,.

P. DOUSSINEAU, C. FRENOIS, R. G. LEISURE, A. LEVELUT and J.-Y. PRIEUR J . Physique 4 1 (1980) 1193-1211.