Ultrahigh electric charge density harvested from pre-compressed ferroelectric ceramics

Ferroelectric elements of high-power electrical generators, utilizing the ability of ferroelectric materials to produce electric charge under mechanical stress, are subjected to either high-pressure shock or moderate-pressure impact loading. The results are reported herein on experimental investigations of a different mode for the generation of a high electric charge density, one that utilizes pre-compressed ferroelectric ceramics. Hard PZT 52/48 (Navy Type I/PZT-4) ferroelectric ceramic specimens were subjected to static uniaxial compressive stress parallel to polarization. At the moment of operation, the output terminals of the specimens were connected to an external circuit, and the applied stress was quickly removed, resulting in the generation of electric charge. The results indicate that this new method for harvesting electric charge from pre-compressed ferroelectrics produced a surface charge density of 7.4 μC/cm2 upon release of 71 MPa compressive stress, significantly higher than that calculated using the linear piezoelectric charge coefficient d33. Under pre-compressive stresses exceeding 3 MPa, d33 exhibits a nonlinear increase. Higher order terms were introduced into the electro-mechanically coupled constitutive law to model the observed behavior. No degradation of piezoelectric properties or mechanical failure of the ferroelectric specimens was detected over the full range of stress investigated, 0.4–71 MPa. Multi–element ferroelectric modules had no significant electric charge losses after 168 h of 35.4 MPa compression. Therefore, pre-compressed ferroelectrics are capable of producing large electric charges during millisecond time intervals and can be used as high-power energy storage devices.