Lead-free dielectric relaxor ferroelectric (RFE) ceramics are one of the promising materials for dielectric energy storage applications. However, the contradiction between high polarization and low hysteresis leads to interior energy storage performance, which greatly limits their applications in high/pulsed power systems. Here, we propose an effective strategy to significantly improve the energy storage properties of 0.94Bi_0.5Na_0.5TiO₃–0.06BaTiO₃ (0.94BNT–0.06BT) with a morphotropic phase boundary (MPB) composition by constructing multiscale polymorphic domains and local heterogeneous structures. The introduction of Nd(Mg_1/2Hf_1/2)O₃ (NMH) facilitates the formation of short-range ordered polar nanoregions (PNRs). Moreover, small amounts of nanodomains with high polarization are resulted from local heterogeneous structures with Bi- and Ti-rich regions. Multiscale polymorphic domains with the coexistence of rhombohedral/tetragonal (R+T) nanodomains and PNRs ensure both high polarization and low hysteresis, which is crucial for improving the energy storage performance. Furthermore, the excellent electrical insulation is resulted from the high insulation resistivity, grain size at the submicron scale and a wide band gap by NMH doping. Therefore, a high recoverable energy density (W_rec) of 7.82 J/cm³ with an ultrahigh efficiency (η) of 93.1% is realized in the designed BNT–BT–NMH ternary system because of both a large ΔP and high E_b. These findings, together with good temperature/frequency/cycling stability, indicate that the optimum composition ceramics are very promising materials for energy storage applications in high/pulsed power systems.

The electrocaloric effect (ECE), known for its environmentally friendly characteristics, holds significant promise for advancing next-generation solid-state refrigeration technologies. Achieving a large ECE along with a wide working temperature range near room temperature remains a key developmental goal. In this study, we successfully obtained a substantial ECE of 1.78 K and an extensive working temperature range of 103 K (ΔT > 1.52 K) near room temperature in CaZrO₃-modified BaTiO₃ lead-free ferroelectric ceramics. Furthermore, this achievement was verified using direct methods. The piezoresponse force microscopy (PFM) results suggest that the broad temperature range is attributed to the formation of ferroelectric microdomains and polar nanoregions (PNRs). Furthermore, X-ray photoelectron spectroscopy (XPS) and ultraviolet‒visible (UV‒Vis) spectroscopy reveal a decrease in the oxygen vacancy concentration and an increase in the bandgap for higher CaZrO₃ doping levels. These changes synergistically enhance the maximum applied electric field, helping to achieve a high-performance ECE near room temperature. This research presents a straightforward and effective approach for achieving high-performance ECEs in BaTiO₃ lead-free ceramics, offering promising prospects for application in next-generation solid-state refrigeration technologies.

The electrocaloric effect (ECE) offers a pathway to environmentally sustainable and easily miniaturized refrigeration technology, positioning it as a front-runner for the next generation of solid-state cooling solutions. This research unveils a remarkable ECE in a finely tuned (Ba_0.86Ca_0.14)_0.98La_0.02Ti_0.92Sn_0.08O₃ ceramic, exhibiting a temperature shift (ΔT) of 1.6 K across more than 85% of the maximum ΔT (ΔT_max) and spanning an exceptionally wide operational range of 92 K. Our investigation on dielectric responses and ferroelectric polarization-electric field (P–E) loops suggests that the broad operational scope results from the fragmentation of extended ferroelectric domains into smaller domains and polar nano-regions (PNRs) supported by PFM analysis. Furthermore, the introduction of La enhances spontaneous polarization by significantly extending the maximum electric field that can be applied, facilitating high-performance ECE at ambient temperature. This study positions BaTiO₃-based lead-free ceramic as a sustainable alternative for addressing the cooling demands of modern electronic components, marking a significant stride toward next-generation solid-state refrigeration.

Ferroelectric thin/thick films with large electrocaloric (EC) effect are critical for solid state cooling technologies. Here, large positive EC effects with two EC peaks in a broad temperature range (~100 K) were obtained in 0.95Pb_0.92La_0.08(Zr_0.70Ti_0.30)_0.98O₃-0.05BiFeO₃ (BFOLa-codoped PZT) epitaxial thin films deposited on the (100), (110) and (111) oriented SrTiO₃ (STO) substrates by a sol-gel method. The thin film deposited on the (111) oriented STO substrate exhibited a stronger EC effect (~20.6 K at 1956 kV/cm) near room temperature. However, the thin films deposited on the (100) and (110) oriented STO substrates exhibited a stronger EC effect (~18.8 K at 1852 kV/cm and ~20.8 K at 1230 kV/cm, respectively) around the peak of the dielectric permittivity (T_m, ~375 K). Particularly, as the direction of the applied electric field was switched (E < 0), the ΔT of the (100)-oriented thin films around T_m was enhanced significantly from 18.8 K to 38.1 K. The self-induced-poling during the preparing process maybe plays a key role on the magic phenomenon. It can be concluded that the BFOLa-codoped PZT epitaxial thin films are promising candidates for application in the next solid-state cooling devices.