A mechanism of electric charge losses in adiabatically compressed ferroelectrics

Abstract

A ferroelectric depolarized by high strain-rates induced by the passage of adiabatic shock waves releases a high-density electric charge, initiating the generation of high voltage and megawatt power levels. Additionally, this depolarization process alters physical and mechanical properties that might cause energy and electric charge losses in the ferroelectric materials. We report, herein, the results of an experimental study of electric charge losses in Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3 ferroelectrics subjected to shock compression. We found that electric charge losses mainly occur in the compressed zone of ferroelectric elements; i.e., shock compression is an essential part of the charge loss mechanism. Based on our analysis of the experimental results, charge losses are explained by the leakage current flowing through microscopic conductive pathways (conductive channels), which are formed due to the effects of high magnitude stress and high electric fields in compressed zones of ferroelectric elements. It is shown that the Joule heating of conductive channels by the leakage current increases their temperature and conductance, eventually short-circuiting the electrodes of the shocked ferroelectric element and causing electric breakdown. The leakage current density, jleak, and breakdown delay time, tcr, can be described by the relationship, jleak2tcr=β (where β is the material dependent constant), over a wide range of delay times. The breakdown criterion we propose is based on the integral of specific current action and can be used to characterize the electric breakdown in a broad range of shock-compressed ferroelectric materials.