Nonlinear electroacoustic phenomena: Phonon echo in d-tartaric acid and its salts

The phonon echo, also called polarization or electroacoustic echo, is investigated for d-tartaric acid and its diammonium salt as well as for the Rochelle salt by using the two-pulse technique. The dependence of the echo amplitude on the delay time is described by both the anharmonic oscillator model and the model of coupled micromotions of the grains recently proposed by Pouget and Maugin. The echo under the experimental conditions behaves according to the small signal limit. The dependence of the damping factor on the pressure of the surrounding gas and the temperature is used respectively to measure an average speed of sound and to derive the mechanism of damping. Under vacuum, the damping factor is found to depend on the square of the radio frequency (rf) as is expected from an intrinsic loss mechanism. A plot of the temperature dependence of the damping factor for d-tartaric acid exhibits a maximum. This maximum is explained by a thermally activated acoustic relaxation within the powder particles. The observed deuteration effect both on the shape and the position of the maximum points out the importance of hydrogen motions for the acoustic relaxation in these hydrogen-bonded solids.