Micro-Structure Of The Black Spots Formed During Piezo-Ceramic Degradation And Its Influences On Electrical Properties

The piezoelectric ceramics,especially PZT ceramics,with desirable features including electric properties and low cost have been widely applied in the various electronic equipment.However,piezoelectric ceramic is driven by a DC electric field in partial applications.The electrical degeneration refer to the phenomenon that the electric resistance decreases and leakage current increases of piezoelectric ceramics with the effect of DC load,which could therefore reduce the reliability and service life.Presently,The theory on electric degeneration of piezoelectric ceramics has not been refined.In addition,the relationship of electric degeneration and black spot has not been carefully investigated.The effect of doping on electric degeneration,the effect of high temperature and humidity on self-recovery and electric degeneration,the effect of side-left on the electric degeneration,and the electric degeneration process of lead-free ceramics as well as the microstructure morphology of black spots have been investigated.The cross section of black spots was analyzed by optical microscope(OM)and scanning electron microscope(SEM).The phase structure was characterized by X-ray diffraction(XRD)and Raman spectra.The revealing results indicates that doping can accelerate the rate of electrical degradation of piezoelectric ceramics,and the rate of soft doping is faster than that of hard doping;in the condition of high temperature and humidity,the rate of electrical degradation and self-recovery of PZT piezoelectric ceramics is faster than those of doped ceramic,moreover,the influence of temperature is greater than the humidity.In the same working condition,the samples covered full of Ag layer could obtain great amounts and lager sizes of black spots than that of side-left samples.The electric degeneration of lead ceramics is easier occurred than that of lead-free ceramics.The microstructure and phase structure of black spots have been analyzed,and the growth phenomenon of black spots has clarified.The above-mentioned mechanisms could be helpful to refine the theory on electric degeneration.