Gradient-Structured Ceramics with High Energy Storage Performance and Excellent Stability

Owing to the high power density, eco-friendly, and outstanding stability, the lead-free ceramics have attracted great interest in the fields of pulsed power systems. Nevertheless, the low energy storage density of such ceramics is undoubtedly a severe problem in practical applications. To overcome this limitation, the lead-free ceramics with gradient structures are designed and fabricated using the tape-casting method herein. By optimizing the composition and distribution of the gradient-structured ceramics, the energy storage density, and efficiency can be improved simultaneously. Under a moderate electric field of 320 kV cm⁻¹, the value of recoverable energy storage density (W_rec) is higher than 4 J cm⁻³, and the energy storage efficiency (η) is of ≥88% for 20-5-20 and 20-10-20. Furthermore, the gradient-structured ceramics of 20-10-0-10-20 and 20-15-0-15-20 possess high applied electric field, large maximum polarization, and small remnant polarization, which give rise to ultrahigh W_rec and η on the order of ≈6.5 J cm⁻³ and 89–90%, respectively. In addition, the energy storage density and efficiency also exhibit excellent stability over a broad range of frequencies, temperatures, and cycling numbers. This work provides an effective strategy for improving the energy storage capability of eco-friendly ceramics.     

Synergistic Optimization of Energy Storage Density of PYN-Based Antiferroelectric Ceramics by Composition Design and Microstructure Engineering

PbYb_0.5Nb_0.5O₃ (PYN)-based ceramics, featured by their ultra-high phase-switching field and low sintering temperature (950 °C), are of great potential in exploiting dielectric ceramics with high energy storage density and low preparation cost. However, due to insufficient breakdown strength (BDS), their complete polarization-electric field (P-E) loops are difficult to be obtained. Here, to fully reveal their potential in energy storage, synergistic optimization strategy of composition design with Ba²⁺ substitution and microstructure engineering via hot-pressing (HP) are adopted in this work. With 2 mol% Ba²⁺ doping, a recoverable energy storage density (W_rec) of 10.10 J cm⁻³ and a discharge energy density (W_dis) of 8.51 J cm⁻³ can be obtained, supporting the superior current density (C_D) of 1391.97 A cm⁻² and the outstanding power density (P_D) of 417.59 MW cm⁻². In situ characterization methods are utilized here to reveal the unique movement of the B-site ions of PYN-based ceramics under electric field, which is the key factor of the ultra-high phase-switching field. It is also confirmed that microstructure engineering can refine the grain of ceramics and improve BDS. This work strongly demonstrates the potential of PYN-based ceramics in energy storage field and plays a guiding role in the follow-up research.     

Enhanced large field-induced strain and energy storage properties of Sr0.6La0.2Ba0.1TiO3-modified Bi0.5Na0.5TiO3 relaxor ceramics

Dielectric materials especially relaxor ferroelectrics with giant strain and super-high energy density have received substantial attentions. Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics as one of the typical relaxor ferroelectric materials have been extensively explored for their distinctive performance. Here, lead-free (1?x)Na_0.5Bi_0.5TiO₃–xSr_0.6La_0.2Ba_0.1TiO₃ (BNT–SLBT) ceramics were designed and prepared by the solid-state reaction method. A large strain response of 0.470% and huge piezoelectric strain coefficient of 600 pm/V were achieved in BNT–0.15SLBT relaxor, which were attributed to the relaxor-ferroelectric phase transition under stimulated electric field. The ε_r–T curve shows that with the increase of x content, the phase transition temperature moves to room temperature, which improves the energy storage performance. A super-high recoverable energy density W_rec of 3.18 J/cm³ and η of 82.8% under 250 kV/cm can be achieved in BNT–0.25SLBT ergodic relaxor. Moreover, the charge–discharge properties characterized by a high pulse discharge energy density (0.816 J/cm³), a rapid discharge duration (3 μs) and a power density (2.86 MW/cm³) are also observed in BNT–0.25SLBT ceramic. We provide a method for enhanced BNT-based ceramics with strain and energy storage in drive device or capacitor, facilitating the exploration of ceramic in the future.

     

Giant Energy Storage Density with Antiferroelectric-Like Properties in BNT-Based Ceramics via Phase Structure Engineering

Driven by the information industry, advanced electronic devices require dielectric materials which combine both excellent energy storage properties and high temperature stability. These requirements hold the most promise for ceramic capacitors. Among these, the modulated Bi_0.5Na_0.5TiO₃ (BNT)-based ceramics can demonstrate favorable energy storage properties with antiferroelectric-like properties, simultaneously, attaching superior temperature stability resulted from the high Curie temperature. Inspired by the above properties, a strategy is proposed to modulate antiferroelectric-like properties via introducing Ca_0.7La_0.2TiO₃ (CLT) into Bi_0.395Na_0.325Sr_0.245TiO₃ (BNST) ((1−x)BNST-xCLT, x = 0.10, 0.15, 0.20, 0.25). Combining both orthorhombic phase and defect dipole designs successfully achieve antiferroelectric-like properties in BNST-CLT ceramics. The results illustrate that 0.8BNST-0.2CLT presents superior recoverable energy storage density ≈8.3 J cm⁻³ with the ideal η ≈ 80% at 660 kV cm⁻¹. Structural characterizations demonstrate that there is the intermediate modulated phase with the coexistence of the antiferroelectric and ferroelectric phases. In addition, in situ temperature measurements prove that BNST-CLT ceramics exhibit favorable temperature stability over a wide temperature range. The present work illustrates that BNT-based ceramics with antiferroelectric-like properties can effectively enhance the energy storage performance, which provides novel perspectives for the subsequent development of advanced pulsed capacitors.     

Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (E_b) and the difference between maximum polarization (P_max) and remnant polarization (P_r), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO₃ into Bi_0.5Na_0.5TiO₃ is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase P_max). Then Sr(Al_0.5Ta_0.5)O₃ (SAT)-doped 0.94 Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P_r). Finally, a large recoverable energy density (W_rec) of 8.33 J cm⁻³ and a high energy efficiency (η) of 90.8% under 555 kV cm⁻¹ are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance E_b), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W_rec > 5.0  cm⁻³, η > 90%) at 400 kV cm⁻¹. This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics.     

High-Energy Storage Density and Efficiency of the xBi(Mg2/3Nb1/3)O3-(1 − x)(Ba0.8Sr0.2)TiO3 (0.08 ≤ x ≤ 0.14) Lead-Free Perovskite Structured Ceramics

The compounds xBi(Mg_2/3Nb_1/3)O₃-(1 − x)(Ba_0.8Sr_0.2)TiO₃ (xBMN-(1 − x)BST, 0.08 ≤ x ≤ 0.14) are prepared via the traditional solid-state reaction method and the ceramics are well densified in the sintering temperature range of 1280–1330 °C. X-ray diffraction analysis shows that all the ceramics crystallize into perovskite structure. Proper amounts of BMN additions can effectively reduce grain sizes of the xBMN-(1 − x)BST ceramics, resulting in more uniform microstructures. Accordingly, breakdown strength E_b is improved and a maximum value 250 kV cm⁻¹ is obtained in ceramic with x = 0.10. Meanwhile, recoverable energy storage density W_rec of the 0.1BMN-0.9BST ceramics reaches 2.03 J cm⁻³, and energy storage efficiency (η) is 96.8%. When the operating temperature increases to 150 °C, the W_rec and η values are about 1.02 J cm⁻³ under 150 kV cm⁻¹ and 89.8%, respectively.     

Improved energy storage and electrocaloric properties of lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramic

Lead-free Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃ (BCZT) ceramic powders were synthesized using the sol–gel method. The ceramics thickness was reduced to achieve high-energy storage and large electrocaloric effect in bulk ceramics. Dielectric, ferroelectric, energy storage, and electrocaloric properties were investigated for BCZT ceramic with 400 µm. Here, pure crystalline structure and homogenous microstructure were identified by XRD analysis and SEM measurements, respectively. The dielectric measurements revealed a maximum dielectric constant associated with ferroelectric–paraelectric phase transition. The maximum of \(\varepsilon^{\prime}_{{\text{r}}}\) was 17841, around 352 K. Furthermore, the BCZT ceramic exhibited improved energy storage and electrocaloric properties. A high recoverable energy density W_rec of 0.24 J/cm³ and a total energy density W_total of 0.27 J/cm³ with an efficiency coefficient of?~?88% at 423 K under an electric field of 55 kV/cm were obtained. Besides, The maximum value of ΔT?=?2.32 K, the electrocaloric responsivity ζ?=?0.42 K mm/kV, the refrigeration capacity RC?=?4.59 J/kg and the coefficient of performance COP?=?12.38 were achieved around 384 K under 55 kV/cm. The total energy density W_total and the temperature change ΔT were also calculated by exploiting the Landau–Ginzburg–Devonshire (LGD) theory. The theoretical results matched the experimental findings. These results suggest that the synthesized BCZT ceramic with reduced thickness could be a promising candidate for energy storage and electrocaloric applications.

     

Delayed Polarization Saturation Induced Superior Energy Storage Capability of BiFeO3-Based Ceramics Via Introduction of Non-Isovalent Ions

Electrostatic capacitors are emerging as a highly promising technology for large-scale energy storage applications. However, it remains a significant challenge to improve their energy densities. Here, an effective strategy of introducing non-isovalent ions into the BiFeO₃-based (BFO) ceramic to improve energy storage capability via delaying polarization saturation is demonstrated. Accordingly, an ultra-high energy density of up to 7.4 J cm⁻³ and high efficiency ≈ 81% at 680 kV m⁻¹ are realized, which is one of the best energy storage performances recorded for BFO-based ceramics. The outstanding comprehensive energy storage performance is attributed to inhibiting the polarization hysteresis resulting from generation ergodic relaxor zone and random field, and generating highly-delayed polarization saturation with continuously-increased polarization magnitudes with the electric field of supercritical evolution. The contributions demonstrate that delaying the polarization saturation is a consideration for designing the next generation of lead-free dielectric materials with ultra-high energy storage performance.     

Superior Energy Storage Capability and Stability in Lead-Free Relaxors for Dielectric Capacitors Utilizing Nanoscale Polarization Heterogeneous Regions

The development of high-performance lead-free dielectric ceramic capacitors is essential in the field of advanced electronics and electrical power systems. A huge challenge, however, is how to simultaneously realize large recoverable energy density (W_rec), ultrahigh efficiency (η), and satisfactory temperature stability to effectuate next-generation high/pulsed power capacitors applications. Here, a strategy of utilizing nanoscale polarization heterogeneous regions is demonstrated for high-performance dielectric capacitors, showing comprehensive properties of large W_rec (≈6.39 J cm⁻³) and ultrahigh η (≈94.4%) at 700 kV cm⁻¹ accompanied by excellent thermal endurance (20–160 °C), frequency stability (5–200 Hz), cycling reliability (1–105 cycles) at 500 kV cm⁻¹, and superior charging-discharging performance (discharge rate t_0.9 ≈ 28.4 ns, power density PD ≈161.3 MW cm⁻³). The observations reveal that constructing the polarization heterogeneous regions in a linear dielectric to form novel relaxor ferroelectrics produces favorable microstructural characters, including extremely small polar nanoregions with high dynamics and multiphase coexistence and stable local structure symmetry, which enables large breakdown strength and ultralow polarization switching hysteresis, hence synergistically contributing to high-efficient capacitive energy storage. This study thus opens up a novel strategy to design lead-free dielectrics with comprehensive high-efficient energy storage performance for advanced pulsed power capacitors applications.     

Enhanced energy storage properties in lead-free NaNbO3–Sr0.7Bi0.2TiO3–BaSnO3 ternary ceramic

The urgent requirement of environment-friendly materials with excellent energy storage performance for pulse power systems has sparked considerable research on lead-free ceramics. In this work, a new lead-free 0.90(0.80NaNbO₃–0.20Sr_0.7Bi_0.2TiO₃)–0.10BaSnO₃ ceramic with high recoverable energy storage density (W_r?=?3.51 J/cm³) and decent energy storage efficiency (η?=?70.85%) has been obtained. In particular, these ceramics exhibit an ultrahigh breakdown strength of 402 kV/cm due to the dense microstructure and small grain size. The impedance analysis also reveals that the incorporation of BaSnO₃ is conducive to the enhancement of insulation ability and breakdown strength. Additionally, great thermal stability (ΔW_r?<?10% over 20–120 °C at 200 kV/cm) and fatigue resistance (ΔW_r?<?1% after 120,000 electrical cycles at 200 kV/cm) are observed, indicating that the 0.90(0.80NaNbO₃–0.20Sr_0.7Bi_0.2TiO₃)–0.10BaSnO₃ ceramics have promising application prospect for high-temperature energy storage devices in pulse power applications.

     

Enhanced Crystallinity,Dielectric, and Energy Harvesting Performances of Surface‐Treated Barium Titanate Hollow Nanospheres/PVDF Nanocomposites

Enhancement of the energy harvesting performance and dielectric constants of poly(vinylidene fluoride) (PVDF)‐based capacitors is realized by incorporating 16 wt% of surface‐treated BaTiO₃ hollow nanospheres (HNSs) in comparison with the pristine PVDF. The fabricated BaTiO₃ HNSs with particle sizes of ≈20 nm and BET surface area of 297 m² g⁻¹ are treated by three different surface modifiers. The changes in crystallinity of the PVDF containing the surface‐treated BaTiO₃ HNSs are induced by both enlarged surface areas and increased surface functionality of the HNSs. Effects of such surface functionalities on the crystalline, dielectric, and energy harvesting performances of the nanocomposites are systematically investigated to identify the optimal surface modifier to enhance the energy density of the nanocomposites. Consequently, these changes in crystallinity lead to higher dielectric constants (ε′ ≈ 109.6) and energy density (U_e ≈ 21.7 J cm⁻³) with highly retained breakdown strength (E = 3.81 × 10³ kV cm⁻¹) compared to pristine PVDF (ε′ ≈ 11.6 and U_e ≈ 2.16 J cm⁻³ at 3.98 × 10³ kV cm⁻¹), indicating their potential as high energy density capacitors.     

Energy storage performance of silica-coated k0.5Na0.5NbO3-based lead-free ceramics

Potassium sodium niobate-based ceramics have been extensively studied as high-power energy storage capacitor in recent years due to their excellent dielectric properties. We investigated the microstructure, dielectric-temperature spectrum, and energy storage properties of SiO₂-coated 0.9(k_0.5Na_0.5)NbO₃–0.1Bi(Zn_2/3Nb_1/3)O₃ (0.9KNN–0.1BZN) ceramics prepared by solid-state sintering and Stöber method. During the sintering process, SiO₂ reacted with 0.9KNN–0.1BZN to form the second phase K₃Nb₃O₆Si₂O₇. Coating SiO₂ could improve the dielectric-temperature stability of 0.9KNN–0.1BZN ceramics, and had excellent performance adapting to high-temperature conditions. When the SiO₂ content is 1.0 wt%, the maximum energy storage density of 0.9KNN–0.1BZN ceramics is 0.97 J/cm³, and the breakdown field strength is 200 kV/cm. This work expands the application of (k_0.5Na_0.5)NbO₃ ceramics in the field of energy storage capacitors.

     

Enhanced dielectric temperature stability and energy-storage properties of (Y0.5Nb0.5)4+ co-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free relaxor ceramics

(Bi_0.5Na_0.5)_0.94Ba_0.06Ti_1?x(Y_0.5Nb_0.5)_xO₃ (abbreviated as BNTBT-100xYN) lead-free relaxor ceramics were designed and prepared using a traditional solid-state sintering technique. The influences of the introduction of (Y_0.5Nb_0.5)⁴⁺ complex ions for the dielectric properties and energy storage performances of BNTBT-100xYN ceramics were systematically studied. All samples exhibited a typical pseudo-cubic symmetry structure and obtained the dense microstructure with the uniform distribution of all elements. The ergodic relaxor behavior of all ceramics was observed and revealed a trend of increase as a function of composition. It accelerated the improvement of the temperature stability of the dielectric constant. All samples showed a single grain conduction mechanism and the activation energy decreased with the addition of composition. It is related to the generation of oxygen vacancies induced by the defect dipoles. BNTBT-6YN ceramic revealed excellent dielectric temperature stability within the temperature range from 87 to 479 °C and the loss tangent less than 0.05 between 25 °C and 474 °C. Besides, a high recoverable energy density of?~?0.91 J/cm³ with the corresponding efficiency of?~?78.5% at applied 115 kV/cm field was achieved for BNTBT-5YN ceramic. Hence, BNTBT-5YN and BNTBT-6YN ceramics will become one of the outstanding dielectric ceramics for the electronic components.

     

Dual-Conductive CoSe2@TiSe2-C Heterostructures Promoting Overall Sulfur Redox Kinetics under High Sulfur Loading and Lean Electrolyte

Although lithium–sulfur batteries (LSBs) possess a high theoretical specific capacity and energy density, the inherent problems including sluggish sulfur conversion kinetics and the shuttling of soluble lithium polysulfides (LiPSs) have severely hindered the development of LSBs. Herein, cobalt selenide (CoSe₂) polyhedrons anchored on few-layer TiSe₂-C nanosheets derived from Ti₃C₂T_x MXenes (CoSe₂@TiSe₂-C) are reported for the first time. The dual-conductive CoSe₂@TiSe₂-C heterostructures can accelerate the conversion reaction from liquid LiPSs to solid Li₂S and promote Li₂S dissociation process through high conductivity and lowered reaction energy barriers for promoting overall sulfur redox kinetics, especially under high sulfur loadings and lean electrolyte. Electrochemical analysis and density functional theory calculation results clearly reveal the catalytic mechanisms of the CoSe₂@TiSe₂-C heterostructures from the electronic structure and atomic level. As a result, the cell with CoSe₂@TiSe₂-C interlayer maintains a superior cycling performance with 842.4 mAh g⁻¹ and a low-capacity decay of 0.031% per cycle over 800 cycles at 1.0 C under a sulfur loading of 2.5 mg cm⁻². More encouragingly, it with a high sulfur loading of ≈7.0 mg cm⁻² still harvests a high areal capacity of ≈6.25 mAh cm⁻² under lean electrolyte (electrolyte/sulfur, E/S ≈ 4.5 µL mg⁻¹) after 50 cycles at 0.05 C.     

Homogenizing Zn Deposition in Hierarchical Nanoporous Cu for a High-Current,High Areal-Capacity Zn Flow Battery

A Zn anode can offset the low energy density of a flow battery for a balanced approach toward electricity storage. Yet, when targeting inexpensive, long-duration storage, the battery demands a thick Zn deposit in a porous framework, whose heterogeneity triggers frequent dendrite formation and jeopardizes the stability of the battery. Here, Cu foam is transferred into a hierarchical nanoporous electrode to homogenize the deposition. It begins with alloying the foam with Zn to form Cu₅Zn₈, whose depth is controlled to retain the large pores for a hydraulic permeability ≈10⁻¹¹ m². Dealloying follows to create nanoscale pores and abundant fine pits below 10 nm, where Zn can nucleate preferentially due to the Gibbs–Thomson effect, as supported by a density functional theory simulation. Morphological evolution monitored by in situ microscopy confirms uniform Zn deposition. The electrode delivers 200 h of stable cycles in a Zn–I₂ flow battery at 60 mAh cm⁻² and 60 mA cm⁻², performance that meets practical demands.     

Microstructure,dielectric, and energy storage performance of (Zn1/3Nb2/3)4+ complex-ion modified (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics

In this study, (Ba_0.85Ca_0.15)(Zr_0.10Ti_0.90)_1-x(Zn_1/3Nb_2/3)_xO₃ ceramics were synthesized by conventional solid-phase methods, referred to as BCZT-xZN (x?=?0.0, 0.1, 0.2, 0.3, 0.4). The effects of adding different contents of (Zn_1/3Nb_2/3)⁴⁺ ion on the microstructure, dielectric and ferroelectric properties of BCZT ceramics were studied. Scanning electron microscopy (SEM) results showed that the average particle size of the samples was significantly reduced after the addition of (Zn_1/3Nb_2/3)⁴⁺ ion, and a second phase appeared when the addition amount was?≥?0.3. The dielectric properties show that with (Zn_1/3Nb_2/3)⁴⁺ ion replacing the B-site of BCZT ceramics, the dielectric constant decreases significantly and the Curie temperature decreases below room temperature. At the same time, we observed that the ceramic has good stability to temperature (-150 °C–200 °C) and frequency (10²–10⁶ Hz) changes. The addition of (Zn_1/3Nb_2/3)⁴⁺ ion can significantly reduce the residual polarization and improve the breakdown strength of ceramics. When x?=?0.3, The maximum energy storage density of ceramics is 0.994 J/cm³, which is about four times higher than that of pure BCZT ceramic (0.25 J/cm³). These findings fully demonstrate the great potential of BCZT ceramics in energy storage.

     

Sandwich-Structured Quasi-Solid Polymer Electrolyte Enables High-Capacity,Long-Cycling,and Dendrite-Free Lithium Metal Battery at Room Temperature

The insufficient ionic conductivity, limited lithium-ion transference number (t_Li+), and high interfacial impedance severely hinder the practical application of quasi-solid polymer electrolytes (QSPEs). Here, a sandwich-structured polyacrylonitrile (PAN) based QSPE is constructedin which MXene-SiO₂ nanosheets act as a functional filler to facilitate the rapid transfer of lithium-ion in the QSPE, and a polymer and plastic crystalline electrolyte (PPCE) interface modification layer is coated on the surface of the PAN-based QSPE of 3 wt.% MXene-SiO₂ (SS-PPCE/PAN-3%) to reduce interfacial impedance. Consequently, the synthesized SS-PPCE/PAN-3% QSPE delivers a promising ionic conductivity of ≈1.7 mS cm⁻¹ at 30 °C, a satisfactory t_Li+ of 0.51, and a low interfacial impedance. As expected, the assembled Li symmetric battery with SS-PPCE/PAN-3% QSPE can stably cycle more than 1550 h at 0.2 mA cm⁻². The Li||LiFePO₄ quasi-solid-state lithium metal battery (QSSLMB) of this QSPE exhibits a high capacity retention of 81.5% after 300 cycles at 1.0 C and at RT. Even under the high-loading cathode (LiFePO₄ ≈ 10.0 mg cm⁻²) and RT, the QSSLMB achieves a superior area capacity and good cycling performance. Besides, the assembled high voltage Li||NMC811(loading ≈ 7.1 mg cm⁻²) QSSLMB has potential applications in high-energy fields.     

Overcoming the Trade-Off between Optical Transmittance and Areal Capacitance of Transparent Supercapacitors for Practical Application

It is substantially challenging for transition metal oxide nanoparticle (NP)-based electrodes for supercapacitors to achieve high transparency and large capacity simultaneously due to the inherent trade-off between optical transmittance (T) and areal capacitance (C_A). This study demonstrates how this trade-off limitation can be overcome by replacing some electrode NPs with transparent tin oxide (SnO₂) NPs. Although SnO₂ NPs are non-capacitive, they provide effective paths for charge transport, which simultaneously increase the C_A and T_550nm of the manganese oxide (Mn₃O₄) NP electrode from 11.7 to 13.4 mF cm⁻² and 82.1% to 87.4%, respectively, when 25 wt% of Mn₃O₄ are replaced by SnO₂. The obtained C_A values at a given T are higher than those of the transparent electrodes previously reported. An energy storage window fabricated using the mixed-NP electrodes exhibits the highest energy density among transparent supercapacitors previously reported. The improved energy density enables the window to operate various electronic devices for a considerable amount of time, demonstrating its applicability in constructing a reliable and space-efficient building-integrated power supply system.     

Mg Compensating Design in the Melting-Sintering Method For High-Performance Mg3(Bi,Sb)2 Thermoelectric Devices

N-type Mg₃(Bi, Sb)₂-based thermoelectric (TE) alloys show great promise for solid-state power generation and refrigeration, owing to their excellent figure-of-merit (ZT) and using cheap Mg. However, their rigorous preparation conditions and poor thermal stability limit their large-scale applications. Here, this work develops an Mg compensating strategy to realize n-type Mg₃(Bi, Sb)₂ by a facile melting-sintering approach. “2D roadmaps” of TE parameters versus sintering temperature and time are plotted to understand the Mg-vacancy-formation and Mg-diffusion mechanisms. Under this guidance, high weight mobility of 347 cm² V⁻¹ s⁻¹ and power factor of 34 µW cm⁻¹ K⁻² can be obtained for Mg_3.05Bi_1.99Te_0.01, and a peak ZT≈1.55 at 723 K and average ZT≈1.25 within 323–723 K can be obtained for Mg_3.05(Sb_0.75Bi_0.25)_1.99Te_0.01. Moreover, this Mg compensating strategy can also improve the interfacial connecting and thermal stability of corresponding Mg₃(Bi, Sb)₂/Fe TE legs. As a consequence, this work fabricates an 8-pair Mg₃Sb₂-GeTe-based power-generation device reaching an energy conversion efficiency of ≈5.0% at a temperature difference of 439 K, and a one-pair Mg₃Sb₂-Bi₂Te₃-based cooling device reaching −10.7 °C at the cold side. This work paves a facile way to obtain Mg₃Sb₂-based TE devices at low cost and also provides a guide to optimize the off-stoichiometric defects in other TE materials.     

Ultralow Voltage Manipulation of Ferromagnetism

Spintronic elements based on spin transfer torque have emerged with potential for on-chip memory, but they suffer from large energy dissipation due to the large current densities required. In contrast, an electric-field-driven magneto-electric storage element can operate with capacitive displacement charge and potentially reach 1–10 µJ cm⁻² switching operation. Here, magneto-electric switching of a magnetoresistive element is shown, operating at or below 200 mV, with a pathway to get down to 100 mV. A combination of phase detuning is utilized via isovalent La substitution and thickness scaling in multiferroic BiFeO₃ to scale the switching energy density to ≈10 µJ cm⁻². This work provides a template to achieve attojoule-class nonvolatile memories.