Investigation of the crystal growth, thickness and radial modes of α-BiB₃O₆ piezoelectric crystals

Monoclinic α-BiB₃O₆ (α-BIBO) crystals have been actively studied for various applications. In this paper, large size α-BIBO single crystals were successfully grown by using the top-seeded solution growth method. The thickness extensional (TE) coupling factor k_t and radial extensional (RE) coupling factor k_p for α-BIBO crystals were studied. The equation to evaluate the k_p value for piezoelectric crystals with monoclinic symmetry was deduced based on the internal energy and piezoelectric equations. For α-BIBO crystals, the coupling factor k_t was found to be on the order of 44.0% at room temperature, while the experimental k_p value was determined to be 32.0%, slightly lower than the theoretical value of 33.7%. In addition, the temperature dependence of TE and RE electromechanical properties were studied over the temperature range of 20-600 °C, where k_t was found to show minimal temperature variation, while k_p shifted from 32.0% at room temperature to 27.5% at 600 °C, with a negative variation of −14%. The above electromechanical properties indicate the potential usage of α-BIBO crystals for high temperature piezoelectric devices.