Superior Capacitive Energy Storage of BaTiO3-Based Polymorphic Relaxor Ferroelectrics Engineered by Mesoscopically Chemical Homogeneity

Abstract

Relaxor ferroelectrics exhibit giant potentials in capacitive energy storage, however, the scales of polar nanoregions determine the critical field values where the polarization saturation occurs. In this work, a mesoscopic structure engineered ergodic relaxor state is realized by adjusting submicron-grain scaled chemical homogenity, exhibiting polymorphic polar nanoregions of various scales in different grains. This produces a relatively continuous polarization switching with increasing the applied electric field from diverse grains, thus resulting in a linear-like polarization response feature. As a result, both a giant energy density (W_rec) ≈15.4 J cm^-3 and a field-insensitive ultrahigh efficiency (η) ≈93.2% are simultaneously achieved at 78 kV mm^-1 in (Ba, Ca)(Ti, Zr)O₃-(Bi_0.5Na_0.5)SnO₃ lead-free ceramics. Moreover, both the mesoscopic structure heterogeneity and complex high internal stresses in ultrafine grains decrease the temperature sensitivity of the nanodomain structural features. Together with the suppressed high-temperature defect motion from high ceramic density and submicron grain size, a record-high temperature stability with W_rec = 10.4±5% J cm^-3 and η = 96±3% is obtained at 65 kV mm^-1 and 0-250 °C, demonstrating great application potential of the studied ceramic in high-temperature energy storage capacitors. The proposed strategy in this work greatly expands the design mentality for next-generation high-performance energy-storage dielectrics.

Keywords: energy storage capacitors; ex‐/in situ multiscale structure evolution; mesoscopically chemical homogeneity; polymorphic polar nanodomains; relaxor ferroelectrics.

Figure 1

A diagrammatic sketch of achieving superior capacitive energy‐storage performances in BT‐based polymorphic relaxor FE ceramics engineered by mesoscopically chemical homogeneity. The different colored areas with arrows represent various PNRs with different local FE symmetries.

Figure 2

a) The composition‐structure‐temperature phase diagram for the (1‐x)BCZT‐xBNS conventionally sintered ceramics. b) Rietveld SXRD refinement results for the x = 0.16 SPS ceramic powders. c) SEM images of the x = 0.16 SPS ceramics. The insets of (c) show the grain size distribution and Weibull distribution of the E_B values. d) Room‐temperature P‐E loops measured under the maximum testable electric fields and 10 Hz and the insets of (d) show the corresponding polarization current density‐electric field (J‐E) curve and field‐dependent W_rec and η values of the x = 0.16 SPS ceramics. e‐f) Comparisons of room‐temperature energy‐storage properties between the x = 0.16 SPS samples and other recently reported lead‐free bulk ceramics.^{[ 4} , ⁵ , ⁶ , ⁷ , ⁸ , ⁹ , ¹⁰ , ¹¹ , ¹² , ¹³ , ¹⁶ , ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²² , ³⁰ , ³¹ , ³² , ³³ , ³⁴ , ^{35 ]}

Figure 3

a) Electric field‐/temperature‐dependent P‐E loops measured at 10 Hz and b) evolution of W_rec and η values with electric field and temperature for the SPS ceramics. c) The comparison of thermal stability of W_rec and η values between the SPS ceramic and various recently‐reported representative energy‐storage ceramics.^{[ 11} , ¹² , ³⁷ , ³⁸ , ³⁹ , ⁴⁰ , ^{41 ]}

Figure 4

a) The bright‐field TEM image and corresponding EDS mappings of b) Ba, c) Ti, d) Ca, e) Zr, f) Bi, g) Na, h) Sn elements for the x = 0.16 SPS ceramic. i–l) Dark‐field TEM images of domain morphology for various grains in the x = 0.16 SPS ceramic. m–o) Out‐of‐plane PFM amplitude image of the x = 0.16 SPS ceramic.

Figure 5

a,b) Atomic‐resolution HAADF STEM polarization vector images along [110]_c on two different grains. The red, orange, and blue areas represent the PNRs with O, T, and R symmetries, respectively. c,d) Polarization magnitude mapping and polarization angle mapping as well as e,f) the polarization magnitude and direction distribution of A/B‐site cations obtained from the HAADF images.

Figure 6

a,b) Out‐of‐plane PFM amplitude images of the x = 0.16 SPS ceramic measured at increasing external voltages. c) Raman spectra with changing external electric field for the x = 0.16 SPS sample and evolution of a,b) the (200)c and (220)c SXRD reflections.

Figure 7

a) Evolution of the Raman spectra with changing temperature for the SPS sample. b–g) Out‐of‐plane PFM amplitude images of the SPS sample measured at 10 V on heating. h) Complex AC impedance and fitting semicircles at 500 °C,i) leakage current densities as a function of the external bias electric field for the CS and SPS ceramics. j) Weibull distribution and calculated E_B values of the SPS sample at different temperatures.^{[ 50 ]}