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-Stockbarger crystal grwoth system. The dielectric constant (ε _r), dielectric loss tangent (tanδ) and impedance (Z) of these crystals, monitored along the crystallographica-axis, as a function of frequency in the 100kHz-10MHz range, exhibit sharp resonance effects in the 100–300kHz region. These strong resonance effects are attributed to the piezoelectric nature of the crystal. The origin of the appearance of the sharp peaks in the frequency variation ofε _r and tanδ is in response to the elastic resonances induced via the externally applied electric field. The resonance peak positions shift towards lower frequencies with increase in temperature as a consequence of the decrease in the stiffness coefficient (C ₁₁) of the crystal.