Antiferroelectrics (AFEs) possess great potential for high performance dielectric capacitors, due to their distinct double hysteresis loop with high maximum polarization and low remnant polarization. However, the well-known NaNbO₃ lead-free antiferroelectric (AFE) ceramic usually exhibits square-like P–E loop related to the irreversible AFE P phase to ferroelectric (FE) Q phase transition, yielding low recoverable energy storage density (W_rec). Herein, significantly improved W_rec up to 3.3 J/cm³ with good energy storage efficiency (η) of 42.4% was achieved in Na_0.7Ag_0.3Nb_0.7Ta_0.3O₃ (30Ag30Ta) ceramic with well-defined double P–E loop, by tailoring the A-site electronegativity with Ag⁺ and B-site polarizability with Ta⁵⁺. The Transmission Electron Microscope, Piezoresponse Force Microscope and in-situ Raman spectra results verified a good reversibility between AFE P phase and high-field-induced FE Q phase. The improved stability of AFE P phase, being responsible for the double P–E loop and improved W_rec, was attributed to the decreased octahedral tilting angles and cation displacements. This mechanism was revealed by synchrotron X-ray diffraction and Scanning Transmission Electron microscope. This work provides a good paradigm for achieving double P–E loop and high energy storage density in NaNbO₃-based ceramics.

Macro-fiber composite actuators (MFCAs) suffer from strict restrictions on the utilization of lead-containing precursors due to growing environmental concerns. To address this issue, a novel lead-free MFCA based on potassium sodium niobate piezoceramics has been developed using the dice & fill method. The MFCA demonstrates large electric field-induced displacement (31.4 μm over -500‒1500 V at 0.5 Hz), excellent frequency stability, and a strong linear relationship between the induced displacement and the external voltage amplitude. Meanwhile, unlike lead-based MFCA that requires superposition of a negative dc bias voltage to pursue higher output performance but risks depolarization, lead-free MFCA can achieve larger displacement by superimposing only a positive bias voltage. This device exhibits excellent reliability, maintaining a stable output over 10⁵ electrical cycles. Additionally, a “back-to-back” coupled MFCA has been developed to regulate bidirectional displacement, making it suitable for various practical applications, including active vibration control. This approach has resulted in a 90% vibration reduction and provides new insights into the design of MFCAs, further facilitating their application in active vibration control systems.

Among the lead-free compositions identified as potential capacitor materials, BiScO₃-BaTiO₃ (BS-BT) relaxor dielectrics exhibit good energy storage performance. In this research, 0.4BS-0.6BT is considered as the parent composition, with NaNbO₃ (NN) addition intended to substitute the A and B site cations. The NN modified BS-BT ceramics exhibit excellent temperature stability in terms of their dielectric properties, with the room-temperature dielectric constant on the order of 500–1 000 and variation less than 10% up to 400 ℃. In addition, NN has a high band-gap energy leading to increased breakdown strength and energy storage properties in modified compositions. The highest breakdown strength was achieved for 0.4BS-0.55BT-0.05NN, being on the order of 430 kV/cm, and a high energy density of 4.6 J/cm³ with high energy efficiency of 90% was simultaneously achieved. Of particular importance is that the variation of the energy density was below 5% due to the temperature-insensitive dielectric constant, while ~90% energy efficiency was retained over the temperature range of 25–160 ℃. The improved temperature stability with NN addition makes this composition promising for high temperature capacitor and dielectric energy storage applications.

Dielectric ceramics with high energy storage density and energy efficiency play an important role in high power energy storage applications. In this work, lead free relaxor ferroelectric ceramics in (1-x)Bi_0.51Na_0.47TiO₃- xBa(Zr_0.3Ti_0.7)O₃ (BNT-BZT100x: x = 0.20, 0.30, 0.40 and 0.50) system are fabricated by conventional solid-state sintering method. The BNT-BZT100x ceramics are sintered dense with minimal pores, exhibiting pseudocubic symmetry and strong relaxor characteristic. A high energy storage density of 3.1 J/cm³ and high energy efficiency of 91% are simultaneously achieved in BNT-BZT40 ceramic with 0.1 mm in thickness, at the applied electric field of 280 kV/cm. The temperature stability of the energy density is studied over temperature range of 20–160 ℃, showing minimal variation below 1.5%, together with the excellent cycling reliability (the variations of both energy density and efficiency are below 3% up to 10⁶ cycles), making BNT-BZT40 ceramic promising candidate for high-temperature dielectric and energy storage applications.