Chemical Design of Pb-Free Relaxors for Giant Capacitive Energy Storage

Abstract

Dielectric capacitors have captured substantial attention for advanced electrical and electronic systems. Developing dielectrics with high energy density and high storage efficiency is challenging owing to the high compositional diversity and the lack of general guidelines. Herein, we propose a map that captures the structural distortion (δ) and tolerance factor (t) of perovskites to design Pb-free relaxors with extremely high capacitive energy storage. Our map shows how to select ferroelectric with large δ and paraelectric components to form relaxors with a t value close to 1 and thus obtaining eliminated hysteresis and large polarization under a high electric breakdown. Taking the Bi 0.5 Na 0.5 TiO 3 -based solid solution as an example, we demonstrate that composition-driven predominant order−disorder characteristic of local atomic polar displacements endows the relaxor with a slushlike structure and strong local polar fluctuations at several nanoscale. This leads to a giant recoverable energy density of 13.6 J cm −3 , along with an ultrahigh efficiency of 94%, which is far beyond the current performance boundary reported in Pb-free bulk ceramics. Our work provides a solution through rational chemical design for obtaining Pb-free relaxors with outstanding energy-storage properties.

Local Chemical Clustering Enabled Ultrahigh Capacitive Energy Storage in Pb-Free Relaxors

“…The pressing demand for sustainable and efficient energy storage systems is propelled by their diverse applications, ranging from electric vehicles to microelectronics and beyond. − Dielectric capacitors are optimal energy storage systems characterized by their ultrahigh power density, ultrafast charging/discharging rates, high-voltage endurance, and exceptional reliability, and in particular, being core components in high/pulse power technologies. − However, the use of dielectric capacitors is presently limited by their low energy storage density, especially in situations requiring large capacitances and compact packaging sizes. Consequently, there has been a surge of attention toward developing dielectric capacitors with high energy density and high storage efficiency (“dual high”). − …”

“…Benefiting from the nanoscale heterogeneous polar structure, relaxor ferroelectrics (RFEs) are considered to be an excellent option for “dual high” dielectric capacitors, as exemplified by the achievement of W rec ∼ 10 J cm –3 in bulk RFE ceramics, ,,, and W rec ∼ 150 J cm –3 in RFE thin films under an ultrahigh η (>90%) . The presence of polar nanoregions (PNRs) is a prominent feature of RFEs.…”

“…The sizes, shapes, dipole patterns (including amplitude and symmetry), and volume fractions of PNRs strongly affect their macroscopic properties. For instance, the energy storage properties can be substantially optimized by constructing multiple symmetries PNRs, reducing the size and volume fraction of PNRs as superparaelectric state, , and enhancing the amplitude of dipole to form strong local polar fluctuations. , At the atomic level, compositional heterogeneity is a prerequisite for engineering a polar state. Controlling local chemical heterogeneity, such as increasing local cation disorder, , modifying chemical short-range order, or introducing clustering of RFEs, can yield exceptional properties.…”

Local Heterogeneous Polarization Enhanced Superior Low-Field Energy Storage Performance in Lead-Free Relaxor Ferroelectric Ceramics

“…As shown in Figure c, different from the PNRs at the nanoscale, the LHP is caused by the local component fluctuations at the microscale. Due to the composition difference at various local regions, the local polarizations are inhomogeneous with random polarization strength and angle . As a result, the LHPs respond gradually to the applied electric field, which weakens the nonlinearity of the P – E relation and delays the saturation polarization.…”

Local structure heterogeneity in unique tetragonal BaTiO3-based relaxor featuring ultrahigh electrostrictive effect

“…Relaxor ferroelectrics (RFEs) are featured with strong frequency dispersion of dielectric permittivity, frequency-dependent dielectric maximum ( T m ), and diffuse phase transition (DPT), making them highly attractive for a wide range of applications in sensing, transduction, and energy storage. 1–10 The fascinating properties of RFEs are thought to be linked to their heterogeneous polar structures. 11–17 Initially, RFEs were studied using models based on compositional fluctuations with deviations from completely disordered solid solutions.…”