Piezoelectric properties of quasi one-dimensional conductor (TaSe4)2I

Frequency dependence of the electrical impedance of (TaSe4)2I crystals was studied between 4.2-150K in the frequency range 0.1-20MHz. In all experiments the voltage was applied (and measured) perpendicular to the c axis. We observed a resonance the frequency of which was inversely proportional to the dimension of the sample in the direction of mechanical oscillations, in agreement with the theory of piezoelectric effect. An additional confirmation of the piezoelectric origin of the resonance was found by the excitation of ultrasound waves at 77K in (TaSe4)2I by the intrinsic piezoeffect. We verified that velocity of sound propagation through the sample in both types of experiments was equal to the velocity of C44 sound wave