High Power Characteristics of Piezoelectric Ceramics in Pb(Mn1/3Nb2/3)O3–PbTiO3–PbZrO3 System

As one of high power characteristics of the piezoelectric ceramics in Pb(Mn1/3Nb2/3)O3–PbTiO3–PbZrO3 system, the limit vibration velocity (v max ), is defined as the vibration velocity that generate the fixed temperature rise was evaluated. From this system, a new material with a higher v max of 0.79 m/s which is 1.7 times larger than conventional Pb(Mn1/3Sb2/3)O3–PbTiO3–PbZrO3 system was found. By using this new material, piezoelectric transformers were made and the output electric power (P) of the transformers were measured at R L=(ω·C d2)-1 [load resistance (R L), resonant angular frequency (ω), output damping capacitance (C d2)] and at other fixed resistances. The P of the piezoelectric transformer was measured on this condition, however, measured values of P were smaller than that of the conventional material. In order to clarify this phenomenon, an equivalent circuit including stray capacitance (C f) of the load circuit was proposed. Simulation results by using this equivalent circuit showed that; 1. The load resistance giving the maximum output power decreases, as C f increases. 2. The maximum output power decreases, as C f increases. 3. When C d2 of the piezoelectric transformer is small, the effect of C f on the piezoelectric transformer becomes large. Therefore, a high dielectric constant (ε) is a required characteristic of the piezoelectric ceramic materials for use in the piezoelectric transformer, except for the usually high v max and high electromechanical coupling coefficient (K).