Characterization of piezoelectric ceramics for high-power transducers

The choice of piezoelectric materials for a high-power electromechanical conversion must take into account various factors such as the figure of merit of the material (FOM), the stability of the electromechanical parameters, and the dielectric and mechanical losses. Materials suitable for impact-type igniters must present both a high FOM and a good stability under repetitive shocks. For high-power electromechanical conversion, the FOM of a single piezoelectric bar and of a Langevin-type transducer depends on the ratio of the piezoelectric coefficient d33 over the elastic compliance s33I of the material. Without losses, the limiting factor would be the maximum dynamic stress at a vibration mode. Methods for characterizing the dielectric and mechanical losses under high driving level are given. The electromechanical characteristics and losses of some new compositions are compared with those of standard “hard” materials. An interpretation of the high-level behavior is given taking into account a compensation of the oxidation state of manganese during cooling by a change in the valency of the substitution ions. [Work supported by DCAN.]