Thermal-stable dielectric capacitors with high energy density and power density have attracted increasing attention in recent years. In this work, (1 – x)­Bi0.5Na0.5TiO3–xNaTaO3 [(1 – x)­BNT–xNT, x = 0–0.30] lead-free relaxor ferroelectric ceramics are developed for capacitor applications. The x = 0.20 ceramic exhibits superior thermal stability of discharged energy density (W D) with a variation of less than 10% in an ultrawide temperature range of −50 to 300 °C, showing a significant advantage compared with the previously reported ceramic systems. The W D reaches 4.21 J/cm3 under 38 kV/mm at room temperature. Besides, a record high of power density (P D ≈ 89.5 MW/cm3) in BNT-based ceramics is also achieved in x = 0.20 ceramic with an excellent temperature insensitivity within 25–160 °C. The x = 0.20 ceramic is indicated to be an ergodic relaxor ferroelectric with coexisted R3c nanodomains and P4bm polar nanoregions at room temperature, greatly inducing large maximum polarization, maintaining low remnant polarization, and thus achieving high W D and P D. Furthermore, the diffuse phase transition from R3c to P4bm phase on heating is considered to be responsible for the superior thermal stability of the high W D and P D. These results imply the large potential of the 0.80BNT–0.20NT ceramic in temperature-stable dielectric capacitor applications.

Electrical field dependence of permittivity in (1 − x)AN-xBZN ceramics. Arrow directions down, up and down then up are related to domain switching, field induced transition and domain switching plus field induced transitions, respectively.

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AgNbO3 exhibits “peculiar” anti-/ferroelectricity and narrow bandgap semi-conductivity that leads to active responses to different types of external stimuli, including electric fields, light and mechanical forces. Some of these unique...

Phase behaviour is clarified in the M-phases of AgNbO3 based ceramics which show field-induced phase transitions from antiferroelectric (AFE) to ferroelectric (FE) phases and are of interest for high power energy storage in dielectric capacitors.

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Ferroelectric domain walls (DWs) are important nanoscale interfaces between two domains. It is widely accepted that ferroelectric domain walls work idly at terahertz (THz) frequencies, consequently discouraging efforts to engineer the domain walls to create new applications that utilize THz radiation. However, the present work clearly demonstrates the activity of domain walls at THz frequencies in a lead-free Aurivillius phase ferroelectric ceramic, Ca 0.99 Rb 0.005 Ce 0.005 Bi 2 Nb 2 O 9 , examined using THz-time-domain spectroscopy (THz-TDS). The dynamics of domain walls are different at kHz and THz frequencies. At low frequencies, domain walls work as a group to increase dielectric permittivity. At THz frequencies, the defective nature of domain walls serves to lower the overall dielectric permittivity. This is evidenced by higher dielectric permittivity in the THz band after poling, reflecting decreased domain wall density. An elastic vibrational model has also been used to verify that a single frustrated dipole in a domain wall represents a weaker contribution to the permittivity than its counterpart within a domain. The work represents a fundamental breakthrough in understanding the dielectric contributions of domain walls at THz frequencies. It also demonstrates that THz probing can be used to read domain wall dielectric switching.