Electric field induced degradation of high-voltage PTCR ceramics

Abstract

This study investigates the degradation of the PTCR material BaTiO3 in high DC voltage, as it is important for the application as heater in electric cars. Impedance spectroscopy was used to gain information on the degradation. The different individual contributions (Ri, Qi) are correlated to the respective features of the microstructure. Besides degradation in electric fields, field-free oxidation and reduction were conducted to examine the influence of oxygen vacancy concentration on the resistivity. The results show a higher resistivity after degradation in the electric field and after oxidation. In contrast, reducing the sample decreases the resistivity. The impedance analysis shows that mostly the grain boundary resistance is influenced during degradation. Likely, a local oxygen vacancy redistribution occurs at grain boundaries. This redistribution is caused by the locally very high electric fields, which in turn influence space charge and Schottky barriers, leading to a change in resistivity of the PTCR material.

Keywords

• PTCR ceramics
• Barium titanate
• Degradation
• Heater
• Resistive switching
• Space charge