Significantly reduced conductivity in strontium titanate-based lead-free ceramics by excess bismuth

Abstract

Lead-free dielectric ceramics 0.75SrTiO3-0.25BiFeO3 (ST-BF) with an extra amount of bismuth (Bi) are synthesized by the conventional solid-state reaction method. The crystal structures of ST-BF retain pseudo-cubic phase as Bi content increases. The grain size is found to significantly increase from 1.8 to 4.9 µm and then fall to 3.3 µm in the presence of excess Bi, exhibiting a distinct heterogeneous core–shell microstructure. Impedance spectroscopy data indicates that with increasing excess Bi content to 2 mol%, the shell resistivity increases significantly to ∼ 9 MΩ cm with the largest volume fraction of the shell/core area, and both the core and shell activation energies are increased, resulting in reduced dielectric loss of ∼ 0.08 at 1 kHz and high breakdown strength of ∼ 140 kV cm−1. This work provides a potential strategy for further improvement of ST-BF for capacitor applications.