Phase Transitions in Lead-free Piezoelectric Ceramics Monitored by the Resonance Method

Ferroelectrics, like batio3 (bt) or binatio3 (bnt), were studied in the 1950s and are now revisited, due to the need for lead-free piezoceramics, according to worldwide directives for environmental protection. Poling some of these materials has shown a different physical mechanism than ferroelectric domain orientation, involving field-induced structural phase transitions from pseudo-cubic phases to ferro-piezoelectrically active ones. They also depolarize below the curie temperature due to a structural phase transition. Both poling and thermal depoling can be monitored by the measurement of the electromechanical resonances. Depoling of (1-x) bnt-xbt ceramics with x=0.04 (bnbt4) is here considered as a case study.