Comparison between the Electrical Properties of Bismuth Layer-Structured and Intergrowth Bismuth Layer-Structured Ferroelectric Ceramics

Bismuth layer-structured ferroelectric (BLSF)-type $Bi_4Ti_3O_{12}$ (BiT), $Bi_{3.25}La_{0.75}Ti_3O_{12}$ (BLaT), and $Bi_{3.1}Nd_{0.9}Ti_3O_{12}$ (BNdT) ceramics and intergrowth BLSF-type $BiT-CaBi_4Ti_4O_{15}$ (CBTO), BLaT-CBTO, and BNdT-CBTO ceramics were prepared using the solid-state reaction method. The electrical and the high-temperature properties of the intergrowth BLSF ceramics were compared with those of BLSF ceramics to investigate the possibility of using the former for high-temperature applications. The X-ray diffraction (XRD) analysis revealed well-formed stable structures in all BLSF and intergrowth BLSF ceramics without any second-phase formation. When their electrical properties were examined, the intergrowth BLSF ceramics BiT-CBTO, BLaT-CBTO, and BNdT-CBTO were found to outperform the BLSF ceramics BiT, BLaT, and BNdT, respectively, in terms of the remanent polarization and piezoelectric coefficient values. Among the intergrowth BLSF ceramics, those doped with rare-earth ions La and Nd, i.e., BLaT-CBTO and BNdT-CBTO ceramics, were found to have improved electrical properties compared to the BiT-CBTO ceramics. In particular, the dielectric constants and the piezoelectric coefficients of the BNdT-CBTO ceramics were observed to be as high as 146 and 15.4 pC/N, respectively, which were 28% and 10% higher than those of BNdT ceramics. In the thermal depoling behavior measured to examine high-temperature stability, the intergrowth BLSF ceramics, compared to the BLSF ceramics, demonstrated improvements in the thermal depoling temperature ranging from 100 to $300^{\circ}C$.