Phase and defect structures of MnO2-doped 75BiFeO3–25BaTiO3 ceramics and their effects on electrical properties

Bismuth ferrite (BiFeO 3 )-based high-temperature piezoelectric ceramics have high Curie temperatures and excellent thermal stability; however, their applications are limited by inadequate piezoelectric performance due to large coercive fields and high leakage conduction. This study investigates the impact of MnO 2 doping on the phase transition, defect structure, domain morphology, as well as the dielectric, ferroelectric, and electrical conduction behaviors of 75BiFeO 3 –25BaTiO 3 ceramics sintered under an oxygen atmosphere. A structural transformation from distorted rhombohedral to pseudo-cubic symmetry was observed with increasing MnO 2 content, accompanied by domain fragmentation. MnO 2 doping at an appropriate level inhibited defects such as F e ′ Fe $\ {\mathrm{F}}{{{\mathrm{e^{\prime}}}}_{{\mathrm{Fe}}}}$ and V O 2 − ⋅ ⋅ $V_{{{{\mathrm{O}}}^{{\mathrm{2}} - }}}^{\centerdot \centerdot }$ . Regarding electrical properties, the reduction in rhombohedral distortion and enhancement in the pseudo-cubic phase after MnO 2 doping resulted in decreased remanent polarization and electrostrain, which could potentially hinder piezoelectric response. However, appropriate MnO 2 doping effectively reduced leakage conduction, significantly enhancing the poling efficiency of the ceramics. The maximum d 33 value of 107 pC/N and k p of 0.36 were achieved at an MnO 2 doping content of 0.1 wt.%. Excessive MnO 2 addition may generate 2 M n ′ Ti − V O 2 − ⋅ ⋅ ${\mathrm{2M}}{{{\mathrm{n^{\prime}}}}_{{\mathrm{Ti}}}}-V_{{{{\mathrm{O}}}^{{\mathrm{2}} - }}}^{\centerdot \centerdot }$ defect dipoles, as indicated by increased coercive field ( E c ) and dielectric loss. The observed increase in high-temperature resistivity with MnO 2 content is primarily attributed to reduced grain size and increased concentration of mobile defects. This study provides valuable insights for further research on the application of 75BiFeO 3 –25BaTiO 3 systems in high-temperature piezoelectric devices.