Double-layered piezoelectric ceramic resonators were fabricated using layer stacking with lead-titanate-based ceramics and strontium-bismuth-niobate (SBN)-based ceramics, which are extremely stable against temperature changes or high-temperature retention. Single-mode resonant characteristics of the second harmonic thickness-extensional (TE2) mode vibration can easily be obtained in those resonators. The dispersion curves of the TE2 vibrations were calculated and the results can explain the single-mode resonant phenomenon in the TE2 mode. SBN-based ceramic materials are quire adequate for the fine-tolerance resonator applications, because their electromechanical coupling coefficients are sufficiently small. Strontium site substitutions for SBN improved the temperature coefficient of frequency.
