ULTRASONIC ATTENUATION BY INTERACTION WITH THE SOFT OPTIC MODE IN KTaO3.
HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS
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Ultrasonic attenuation and velocity in KTaO3 has been measured from 180-900 MHz. over the temperature range 2-300K. Both longitudinal and transverse waves were studied. While for transverse waves the attenuation and velocity behaved normally, for longitudinal waves they showed a rapid temperature dependence at low temperature. The longitudinal attenuation was much larger than the transverse attenuation and showed a large peak at 30K. At 4.2K it varied as the square of the ultrasonic frequency at low frequency. These observations are explained, quantitatively at low temperature and qualitatively over the entire range, in terms of an Akhieser type interaction with the soft optic mode. The Gruneisen constant and k 0 frequency for the soft mode are obtained from the analysis. Also some information about the soft mode dispersion is obtained. The Gruneisen constant so determined is in fair agreement with that determined from a phenomenological theory using electrostrictive constants. The k 0 soft mode frequency is in excellent agreement with Raman and infrared results. The effective relaxation time for the interaction is shown to involve both acoustic and optic mode relaxation times. Author
- Solid State Physics