Investigation of thermally stimulated current in unpoled sodium bismuth titanate-based ferroelectric ceramics

Thermally stimulated current (TSC) has been frequently used to investigate the depolarization and charge redistribution in ferroelectric materials. For this test, the ferroelectric materials are often poled under an electric field. However, in some unpoled ferroelectric materials, thermal-electrical current peaks can also be observed during TSC measurements and the mechanisms for the peaks are not fully understood. In this study, Mg-doped sodium bismuth titanate-based (NBT-based) ceramics were fabricated. Through TSC measurement, we systematically examined the origins of the observed electric current peaks in unpoled NBT-based ceramics. We proposed that the observed current peaks are caused by different mechanisms, including polarity induced during sample preparation, polarized surface layers, and the Seebeck effect or flexoelectric-like response caused by the temperature difference between the two surfaces of tested samples. This work is useful for the understanding of various inhomogeneities existing in ferroelectric ceramics, which may further affect the physical properties of the materials.