Effects of B-site complex cations (Fe0.5Nb0.5)4+ doping on the structure and piezoelectric properties of 0.68BiFeO3-0.32BaTiO3 ceramics

BiFeO 3 -BaTiO 3 (BF-BT) ceramics have emerged as a prominent research focus in the lead-free materials field in recent years due to their high Curie temperature and excellent ferroelectric and piezoelectric properties. In this work, 0.68BiFeO 3 -0.32BaTi 1- x (Fe 0.5 Nb 0.5 ) x O 3  + 0.1 wt.% MnO 2 ceramics (abbreviated as 0.68BF-0.32BT(FN) x -Mn, x  = 0, 0.01, 0.02, 0.03, 0.04) were prepared by the conventional solid-state reaction method. The effects of Ti-site (Fe 0.5 Nb 0.5 ) 4+ substitution on the crystal structure, microstructure, dielectric, ferroelectric, and piezoelectric properties of 0.68BF-0.32BT ceramics were systematically investigated. It is confirmed from the XRD results that all the compositions consist of diphasic tetragonal (T) and rhombohedral (R) phases. Increase of B-site (Fe 0.5 Nb 0.5 ) 4+ substitution induces an expansion of unit cell volume, reduces the ferroelectric–paraelectric phase transition temperature ( T m ) monotonically from 471 °C at x  = 0 to 445 °C at x  = 0.04. The average grain size and piezoelectric properties increase by the substitution 2.0 mol% (Fe 0.5 Nb 0.5 ) 4+ complex cations for Ti 4+ in 0.68BF-0.32BT ceramics. Notably, the piezoelectric properties of this ceramic are improved through the grain size effect. Specifically, the 0.68BF-0.32BT(FN) 0.02 -Mn ceramics display optimal comprehensive electrical performance with T m  = 461 °C, P max  = 26.4 µC/cm 2 , P r  = 18.1 µC/cm 2 , E C  = 23.0 kV/cm, d 33  = 151 pC/N, k p  = 0.298, Q m  = 50.32, demonstrating the potential viability of BF-BT ceramics for high-temperature lead-free piezoelectric applications.