High energy-storage performance under low electric fields and enhanced electric-field-induced strain in Nb ⁵⁺ doped BNT−BT lead-free piezoceramics

Advancements in technology and the need for compact electronics have raised the demand for materials with both high energy-storage density and electric-field induced strain. In this study, lead-free (Bi0.465Na0.465Ba0.07)NbxTi(1–x)O3 piezoelectric ceramics, x = 0–0.05, were prepared by conventional solid-state reaction method. All samples exhibited single-phase perovskite structure, with Rietveld refinement revealing the coexistence of tetragonal (P4bm) and rhombohedral (R3c) phases. Increasing Nb content lowered TF-R below room temperature at x ≥0.02, indicating a transition from non-ergodic relaxor (NER) to ergodic relaxor (ER) phase. This phase shift resulted in a maximum strain of 0.27%, corresponding to normalized strain (d33*= Smax/Emax) of 386 pm/V at 70 kV/cm, achieved at x = 0.01. Additionally, Nb doping significantly increased resistivity (~1 order of magnitude) and activation energy (Ea) values, thereby enhancing electrical breakdown strength (Eb). This, combined with decreasing Pr to near-zero from ergodic relaxor, led to a remarkably high energy density (Wrec) of 1.73 J/cm3 and an energy storage efficiency (η) of 82% under a relatively low electric field of 130 kV/cm at x = 0.04. These results demonstrated that optimal Nb doping can simultaneously improve the electro-strain and energy-storage performance of 0.93BNT–0.07BT ceramics, making them promising for actuator and energy-storage applications.