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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