Abstract

 

Nonlinear Acoustic Properties of Layered Crystals

L.A.Kulakova (Ioffe Physico-Technical Institute RAS, St.Petersburg, Russia)

e-mail: L.Kulakova@pop.ioffe.rssi.ru

Anomalies of acoustic properties of layered crystals are presented in this paper. Attenuation and velocity of sound have been investigated in wide range of frequencies (250 - 1800 MHz) and temperatures (100 - 300K). Study of the elastic nonlinearity by direct measuring of the ultrasound high harmonics generation has been carried out. Acoustooptic and pulse-echo techniques were used. It has been shown, that high anisotropy of mechanical strength of layered crystals arises from high anisotropy of bonding forces anharmonicity. It results in the extremely large value of the nonlinear elastic coefficient across the layers and the anharmonicity constant of the appropriate longitudinal phonon modes. High anharmonicity noticeably increases the linear thermal expansion coefficient across the layers, but does not change noticeably the average value of Gruneisen parameter.

 

Section : 2