Evaluation of large signal minor loop behavior in PMN-PT ceramics

The stress and polarization behavior of a lanthanum doped PMN-PT was evaluated using unipolar and biased drives of up to 1.3 MV/m under varying temperatures and mechanical stresses. In particular, the behavior of the strain vs. field and polarization vs. field loops for biased minor loops is be compared to that of the full unipolar drives. It is shown that, as the hysteresis of a material increases, the minor loops tend to rotate around the midline of the major loop. This leads to smaller values for the large signal piezoelectric and dielectric constants than would be predicted from the major loop alone. The behavior of several material performance measures, such as the strain energy density, electromechanical coupling factor and dielectric loss factor, are analyzed as functions of the DC bias and AC drive fields. It is shown that the energy density and coupling factor tend to increase with DC bias field but decrease with AC drive. The dielectric loss factor, on the other hand, decreases as either the DC bias or AC drive fields are increased.