Destruction mechanism of multilayer ceramic actuators

The destruction mechanism in multilayer ceramic actuators under cyclic electric fields has been investigated. Crack propagation has been observed dynamically using CCD (charge-coupled device) microscopy, and the accompanying characteristics of the induced displacement and acoustic emission were measured simultaneously. The piezoelectric Pb(Ni _1/3Nb_2/3)O₃-PbTiO₃ and the phase-transition-related actuator material (antiferroelectric) PbZrO₃-PbSnO₃-PbTiO₃ exhibit a marked difference in the manner of destruction, probably due to the strain-induction mechanism. In the piezoelectrics, the crack initiated near the edge of the internal electrode and propagated basically in three directions: two cracks moved toward the outside electrostrictively inactive region, forming an angle of 100° with each other, while the third moved along the ceramic-electrode interface. In antiferroelectrics, the crack began slightly inside the edge of the internal electrode and propagated along the center area between the pair electrodes. Later crack branches were generated around the electrode edge. A very smart actuator system containing a safety feedback function, which can stop an actuator drive safely without causing any serious damage to the work, e.g., in a precision lathe machine, is proposed