Energy Trapping Characteristics of Bismuth Layer Structured Compound CaBi₄Ti₄O₁₅

Abstract

Piezoelectric characteristics of bismuth layer structured compound CaBi 4 Ti 4 O 15 ceramics were studied in terms of the energy trapping phenomenon of the second harmonic thickness extensional (TE2) vibration mode. An electrode-buried-type resonator was prepared by the co-firing technique to generate the TE2 mode, and frequency-lowering-type energy trapping was realized. Favorable resonant characteristics were obtained for piezoelectric filter and oscillator applications with narrow frequency tolerances, which require a small electromechanical coupling coefficient and a high mechanical quality factor. The electromechanical coupling coefficient for the TE2 vibration mode of the resonator was 13.9% and the mechanical quality factor Q m was 2560. The temperature coefficient of the resonance frequency was adequate for the applications. The microstructure of CaBi 4 Ti 4 O 15 ceramic was also investigated. Marked shape anisotropy of the grain was observed; however, preferential grain orientation was not recognized when the ceramic was prepared by the ordinary firing process.