Is non-stoichiometric crystalline Na β-alumina an ideal amorphous material ? An ultrasonic answer P. Doussineau, R.G. Leisure, A. Levelut et J.-Y. PrieurJ. Physique Lett., 41 3 (1980) 65-68DOI: https://doi.org/10.1051/jphyslet:0198000410306500
