Towards multicaloric effect with ferroelectrics

This work was supported in part by the National Science Foundation (Grant No. CMMI-#1361713) and by DOE Ames Laboratory on “The Caloric Materials Consortium”. L.B. acknowledges the support of ARO Grant No. W911NF-16-1-0227. B.D. acknowledges a public grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” program (Grant No. ANR-10-LABX-0035, Labex NanoSaclay) and Fonds National de la Recherche du Luxembourg (FNR) through InterMobility Project No. 16/1159210 “MULTICALOR”.Utilizing thermal changes in solid state materials strategically offers caloric-based alternatives to replace current vapor-compression technology. To make full use of multiple forms of the entropy and achieve higher efficiency for designs of cooling devices, the multicaloric effect appears as a cutting-edge concept encouraging researchers to search for multicaloric materials with outstanding caloric properties. Here we report the multicaloric effect in BaTiO3 single crystals driven simultaneously by mechanical and electric fields and described via a thermodynamic phenomenological model. It is found that the multicaloric behavior is mainly dominated by the mechanical field rather than the electric field, since the paraelectric-to-ferroelectric transition is more sensitive to mechanical field than to electric field. The use of uniaxial stress competes favorably with pressure due to its much higher caloric strength and negligible elastic thermal change. It is revealed that multicaloric response can be significantly larger than just the sum of mechanocaloric and electrocaloric effects in temperature regions far above the Curie temperature but cannot exceed this limit near the Curie temperature. Our results also show the advantage of the multicaloric effect over the mechanically-mediated electrocaloric effect or electrically-mediated mechanocaloric effect. Our findings therefore highlight the importance of ferroelectric materials to develop multicaloric cooling.PostprintPeer reviewe

Constructing phase boundary in AgNbO3 antiferroelectrics: pathway simultaneously achieving high energy density and efficiency

© 2020, The Author(s). Dielectric capacitors with high energy storage density (Wrec) and efficiency (η) are in great demand for high/pulsed power electronic systems, but the state-of-the-art lead-free dielectric materials are facing the challenge of increasing one parameter at the cost of the other. Herein, we report that high Wrec of 6.3 J cm-3 with η of 90% can be simultaneously achieved by constructing a room temperature M2–M3 phase boundary in (1-x)AgNbO3-xAgTaO3 solid solution system. The designed material exhibits high energy storage stability over a wide temperature range of 20–150 °C and excellent cycling reliability up to 106 cycles. All these merits achieved in the studied solid solution are attributed to the unique relaxor antiferroelectric features relevant to the local structure heterogeneity and antiferroelectric ordering, being confirmed by scanning transmission electron microscopy and synchrotron X-ray diffraction. This work provides a good paradigm for developing new lead-free dielectrics for high-power energy storage applications

Dielectric materials for high-temperature capacitors

Dielectric materials with excellent energy storage capability at elevated temperatures are critical to meet the increasing demand of electrical energy storage and power conditioning at extreme conditions such as hybrid electric vehicles, underground oil industries and aerospace systems. This review study summarises the important aspects and recent advances in the development of nanostructured dielectric materials including ceramics, polymers and polymer composites for high-temperature capacitor applications. The advantages and limitations of current dielectric materials are discussed and analysed. Ongoing research strategies to suppress the conduction loss and optimise the high-temperature capacitive performance of dielectrics have been highlighted. A summary and outlook will conclude this review

Tuning the electrocaloric reversibility in ferroelectric copolymers by a blend approach

In electrocaloric active polymers, the ferroelectric copolymer P(VDF-TrFE) 65/35 mol% exhibits the largest caloric performance ($\Delta S=190.0\ \text{J~K}^{-1}\text{~kg}^{-1}$ , $\Delta T=45.4\ \text{K}$ at an electric field of 100 MV m−1 and 85 °C) due to a sharp first-order phase transition. However, this high property occurs only at the first cycle and then drops significantly in the following electrical cycle, which significantly limits the promising applications of these copolymers. Here we use a blend approach to solve the irreversibility issue. We show that the incorporation of a terpolymer into a copolymer results in the evolution from normal ferroelectric to relaxor, which is accompanied by a large reduction in the thermal hysteresis. As a result, we find that complete reversibility of electrocaloric cycles in blends can be achieved for the copolymer/terpolymer volume ratio as 3/7

Reconstruction of Gut Bacteria in <i>Spodoptera frugiperda</i> Infected by <i>Beauveria bassiana</i> Affects the Survival of Host Pest

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a migratory agricultural pest that is devastating on a global scale. Beauveria bassiana is a filamentous entomopathogenic fungus that has a strong pathogenic effect on Lepidoptera pests but little is known about the microbial community in the host gut and the dominant populations in fungus-infected insects. B. bassiana AJS91881 was isolated and identified from the infected larvae of Spodoptera litura. The virulence of AJS91881 to the eggs, larvae, pupae and adults of S. frugiperda was measured. Moreover, the gut microbial community diversity of healthy and fungus-infected insects was analyzed. Our results showed that after treatment with B. bassiana AJS91881, the egg hatching rate, larval survival rate and adult lifespan of the insects were significantly reduced, and the pupae rigor rate was significantly increased compared to that of the control group. Additionally, the gut microbial community was reconstructed after B. bassiana infection. At the phylum and genus level, the relative abundance of the Proteobacteria and Serratia increased significantly in the B. bassiana treatment group. The KEGG function prediction results showed that fungal infection affected insect gut metabolism, environmental information processing, genetic information processing, organism systems and cellular processes. Fungal infection was closely related to the metabolism of various substances in the insect gut. Serratia marcescens was the bacterium with the highest relative abundance after infection by B. bassiana; intestinal bacteria S. marcescens inhibited the infection of insect fungi B. bassiana against the S. frugiperda. The presence of gut bacteria also significantly reduced the virulence of the fungi against the insects when compared to the group with the larvae fed antibiotics that were infected with fungal suspension (Germfree, GF) and healthy larvae that were infected with fungal suspension prepared with an antibiotic solution (+antibiotic). In conclusion, the reconstruction of the insect intestinal bacterial community is an indispensable link for understanding the pathogenicity of B. bassiana against S. frugiperda. Most importantly, in the later stage of fungal infection, the increased abundance of S. marcescens in the insect intestine inhibited the virulence of B. bassiana to some extent. The findings aid in understanding changes in the gut microbiota during the early stages of entomopathogenic fungal infection of insects and the involvement of insect gut microbes in host defense mediated by pathogenic fungal infection. This study is also conducive to understanding the interaction between entomopathogenic fungi, hosts and gut microbes, and provides a new idea for the joint use of entomopathogenic fungi and gut bacteria to control pests

Thermoelectric coupling effect in BNT-BZT-xGaN pyroelectric ceramics for low-grade temperature-driven energy harvesting

Abstract Pyroelectric energy harvesting has received increasing attention due to its ability to convert low-grade waste heat into electricity. However, the low output energy density driven by low-grade temperature limits its practical applications. Here, we show a high-performance hybrid BNT-BZT-xGaN thermal energy harvesting system with environmentally friendly lead-free BNT-BZT pyroelectric matrix and high thermal conductivity GaN as dopant. The theoretical analysis of BNT-BZT and BNT-BZT-xGaN with x = 0.1 wt% suggests that the introduction of GaN facilitates the resonance vibration between Ga and Ti, O atoms, which not only contributes to the enhancement of the lattice heat conduction, but also improves the vibration of TiO6 octahedra, resulting in simultaneous improvement of thermal conductivity and pyroelectric coefficient. Therefore, a thermoelectric coupling enhanced energy harvesting density of 80 μJ cm−3 has been achieved in BNT-BZT-xGaN ceramics with x = 0.1 wt% driven by a temperature variation of 2 oC, at the optical load resistance of 600 MΩ

Flexible energy harvesting polymer composites based on biofibril-templated 3-dimensional interconnected piezoceramics

Flexible piezoelectric materials have attracted rapidly growing attention because they offer an efficient route to scavenge energies from the living environment to power personal electronics and nanosystems. Current polymer composites with low-dimensional piezoceramic fillers suffer from poor stress transfer from the polymer matrix to the active ceramic fillers, thus significantly limiting the energy harvesting performance. Herein, an interconnected 3D piezoceramic skeleton has been developed by a biofibril template method using the newly developed rare-earth Samarium-doped Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 (Sm-PMN-PT) for flexible piezoelectric polymer composites. When subjected to external mechanical stimulation, the 3D interconnected structure results in effective stress transfer, and consequently, greatly enhanced energy harvesting output. The 3D piezocomposite shows the open-circuit output voltage and short-circuit current density up to ~ 60 V and ~ 850 nA cm −2 , respectively, with the maximum instantaneous power density of ~ 11.5 µW cm −2 which is ~ 16 times higher than that of the conventional nanoparticle-based composite. The remarkable enhancement in the tress transfer ability and piezoelectric response of the biofibril-templated 3D structure have also been verified by phase-field simulations. This work provides a promising paradigm for the development of high-performance flexible energy harvesting materials