Amorphous-like acoustical properties of Na doped β-Al2O 3 P. Doussineau, C. Frénois, R.G. Leisure, A. Levelut et J.-Y. Prieur J. Phys. France, 41 10 (1980) 1193-1211 DOI: 10.1051/jphys:0198000410100119300