Alekseev S.G., Mansfel-d G.D., Nagirny V.P., Polzikova N.I., Sergeev F.O., Chuprik А.А.

Using the method of the bulk acoustic wave resonator spectroscopy the attenuation coefficients of the acoustic waves of the different polarization wave vector directions in langasite and langatate have been measured. The theory connecting the components of the viscosity tensor and the attenuation coefficients has been developed. The losses associated with acoustic wave losses on surface roughness and diffraction losses have been experimentally evaluated using additional measurements at helium temperatures. Using the data of the experiments the values of the full set of the components of the viscosity tensor of the langasite and langatate have been found