Abstract
The (Ba1-x Srx )2NaNb5O15 [BSNN] system is a lead-free ferroelectric material that has large spontaneous polarization and is expected to be applicable for piezoelectric ceramic filter or oscillator devices. Filter and oscillator materials require high temperature stability, and in particular, a small temperature coefficient of resonance frequency in a temperature range from -20 to 80° C (fr-TC). The piezoelectric properties of BSNN ceramics were investigated and it was found that the composition with x=0.6 showed an excellent fr-TC of 15.0 ppm/° C. The composition had anomalies of resonance frequency constant (fr·t) which were considered to arise from ferroelastic phase transitions at -100 and 220° C, and fr·t varied showing a parabolic curve between -100 and 220° C. The temperature at the top of the curve was around 40° C. The temperature dependence of fr·t was fairly small around 40° C because of the inflection of fr·t variation, therefore excellent fr-TC was obtained for the composition.
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