DIELECTRIC-DISPERSION AND PIEZOELECTRIC RESONANCE IN BENZIL SINGLE-CRYSTALS GROWN BY BRIDGMAN-STOCKBARGER TECHNIQUE

Large single crystals of an organic nonlinear optical (NLO) material, benzil, have been grown by employing an indigenously built Bridgman-St ockbarger crystal growth system. The dielectric constant (epsilon(r)), dielectric loss tangent (tan delta) and impedance (Z) of these crysta ls, monitored along the crystallographic a-axis; as a function of freq uency in the 100 kHz-10 MHz range, exhibit sharp resonance effects in the 100-300 kHz region. These strong resonance effects are attributed to the piezoelectric nature of the crystal. The origin of the appearan ce of the sharp peaks in the frequency variation of epsilon(r) and tan delta is in response to the elastic resonances induced via the extern ally applied electric field. The resonance peak positions shift toward s lower frequencies with increase in temperature as a consequence of t he decrease in the stiffness coefficient (C-11) of the crystal.