High energy-storage performance under low electric fields and enhanced electric-field-induced strain in Nb <sup>5+</sup> doped BNT−BT lead-free piezoceramics
Pathit Premwichit, Theeranun Siritanon, Widchaya Somsri, Noppadon Nuntawong, Onthida Kosasang, Sanu K. Gupta, Sasiporn Prasertpalichat
Abstract
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.