Dielectric dispersion and piezoelectric resonance in benzil single crystals grown by Bridgman-Stockbarger technique

Abstract

Large single crystals of an organic nonlinear optical (NLO) material, benzil, have been grown by employing an indigenously built Bridgman-Stockbarger crystal growth system. The dielectric constant (∈r), dielectric loss tangent (tan δ) and impedance (Z) of these crystals, monitored along the crystallographic a-axis, as a function of frequency 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 appearance of the sharp peaks in the frequency variation of ∈r and tan δ 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 (C11) of the crystal.