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1.
Adv Sci (Weinh) ; 6(20): 1901432, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31637170

RESUMO

Ionic evolution-induced phase transformation can lead to wide ranges of novel material functionalities with promising applications. Here, using the gating voltage during ionic liquid gating as a tuning knob, the brownmillerite SrCoO2.5 is transformed into a series of protonated H x SrCoO2.5 phases with distinct hydrogen contents. The unexpected electron to charge-neutral doping crossover along with the increase of proton concentration from x = 1 to 2 suggests the formation of exotic charge neutral H-H dimers for higher proton concentration, which is directly visualized at the vacant tetrahedron by scanning transmission electron microscopy and then further supported by first principles calculations. Although the H-H dimers cause no change of the valency of Co2+ ions, they result in clear enhancement of electronic bandgap and suppression of magnetization through lattice expansion. These results not only reveal a hydrogen chemical state beyond anion and cation within the complex oxides, but also suggest an effective pathway to design functional materials through tunable ionic evolution.

2.
Science ; 366(6464): 475-479, 2019 10 25.
Artigo em Inglês | MEDLINE | ID: mdl-31649196

RESUMO

Ferroelectrics are usually inflexible oxides that undergo brittle deformation. We synthesized freestanding single-crystalline ferroelectric barium titanate (BaTiO3) membranes with a damage-free lifting-off process. Our BaTiO3 membranes can undergo a ~180° folding during an in situ bending test, demonstrating a super-elasticity and ultraflexibility. We found that the origin of the super-elasticity was from the dynamic evolution of ferroelectric nanodomains. High stresses modulate the energy landscape markedly and allow the dipoles to rotate continuously between the a and c nanodomains. A continuous transition zone is formed to accommodate the variant strain and avoid high mismatch stress that usually causes fracture. The phenomenon should be possible in other ferroelectrics systems through domain engineering. The ultraflexible epitaxial ferroelectric membranes could enable many applications such as flexible sensors, memories, and electronic skins.

3.
Nanoscale ; 11(43): 20514-20521, 2019 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-31660549

RESUMO

Ferroelectric topological configurations confined in nanostructures have attracted intensive interest both in fundamental physics and potential applications in non-volatile nanoelectronic devices. However, the preparation approaches such as chemical synthesis and template or electron beam etching inevitably induce damage and contamination; also, these are complicated processes. Herein, by a delicate design of the wetting layer and growth temperature, self-assembled ferroelectric nanoislands were achieved with the BiFeO3/(La,Sr)MnO3/LaAlO3 heterostructure. Based on the thermodynamic analysis, the much lower surface energy (∼0.47 J m-2) of the (La,Sr)MnO3 (∼2-12 nm)/LaAlO3 system than that (∼1.0 J m-2) of BiFeO3 provides the probability for the transformation of layered morphology into nanoislands. From the dynamic perspective, the high growth temperature (∼650-680 °C) helps to step over the energy barrier (∼50 meV per atom) by stimulating the formation of periodically arrayed dislocations at the BiFeO3/(La,Sr)MnO3 interface, which on the one hand releases the epitaxial elastic energy and on the other hand evokes the nucleation of the R-phase nanoisland array. More excitingly, this approach with a wonderful new growth mechanism can also be employed in other ferroelectric model systems such as BaTiO3, which provides a new strategy for the design of novel nanoelectronic devices based on ferroelectric perovskite nanostructures.

4.
Science ; 365(6453): 578-582, 2019 08 09.
Artigo em Inglês | MEDLINE | ID: mdl-31395780

RESUMO

Dielectric capacitors with ultrahigh power densities are fundamental energy storage components in electrical and electronic systems. However, a long-standing challenge is improving their energy densities. We report dielectrics with ultrahigh energy densities designed with polymorphic nanodomains. Guided by phase-field simulations, we conceived and synthesized lead-free BiFeO3-BaTiO3-SrTiO3 solid-solution films to realize the coexistence of rhombohedral and tetragonal nanodomains embedded in a cubic matrix. We obtained minimized hysteresis while maintaining high polarization and achieved a high energy density of 112 joules per cubic centimeter with a high energy efficiency of ~80%. This approach should be generalizable for designing high-performance dielectrics and other functional materials that benefit from nanoscale domain structure manipulation.

5.
ACS Appl Mater Interfaces ; 11(38): 34939-34947, 2019 Sep 25.
Artigo em Inglês | MEDLINE | ID: mdl-31465194

RESUMO

Garnet-type solid electrolytes are suitable for solid-state batteries with a lithium metal anode, but it is challenging to fabricate garnet-based lithium metal batteries with a long cycle life at high rates. This study demonstrates that a mosaic Li7Sn3/LiF interface layer formed in situ on the surface of garnet-type Li6.75La3Zr1.75Ta0.25O12 (LLZT) through the reaction between a SnF2 coating layer and a lithium metal enables stable, high-rate cycling for LLZT-based batteries. The interface layer possesses a nanomosaic structure of Li7Sn3 nanoparticles and surrounding LiF, enabling fast lithium-ion conduction. Meanwhile, ion insulating Li2CO3 on the surface of LLZT pellets is completely removed by SnF2 during the formation of the interface layer, which reduces the ion diffusion barrier from LLZT to the lithium anode. Benefiting from the advantageous interface layer, LiFePO4∥SnF2-LLZT∥Li cells show superior cycle performance over 200 cycles at 1 C (272 µA cm-2) with a capacity of 140.6 mAh g-1 (94.6% retention) at 30 °C. Even at 2 C, a capacity of 102.9 mAh g-1 remains after 200 cycles. This work provides an optimal interfacial structure to enhance lithium-ion migration between garnet electrolytes and a lithium metal and paves the way for developing high-performance solid-state batteries.

6.
ACS Appl Mater Interfaces ; 11(32): 28774-28780, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31314493

RESUMO

Safety is critical to developing next-generation batteries with high-energy density. Polyether-based electrolytes, such as poly(ethylene oxide) and poly(ethylene glycol) (PEG), are attractive alternatives to the current flammable liquid organic electrolyte, since they are much more thermally stable and compatible with high-capacity lithium anode. Unfortunately, they are not stable with 4 V Li(NixMnyCo1-x-y)O2 (NMC) cathodes, hindering them from application in batteries with high-energy density. Here, we report that the compatibility between PEG electrolyte and NMC cathodes can be significantly improved by forming a 2 nm Al2O3 coating on the NMC surface. This nanoscale coating dramatically changes the composition of the cathode electrolyte interphase and thus stabilizes the PEG electrolyte with the NMC cathode. With Al2O3, the capacity remains at 84.7% after 80 cycles and 70.3% after 180 cycles. In contrast, the capacity fades to less than 50% after only 20 cycles in bare NMC electrodes. This study opens a new opportunity to develop safe electrolyte for lithium batteries with high-energy density.

7.
Nat Commun ; 10(1): 2814, 2019 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-31249289

RESUMO

BiCuSeO oxyselenides are promising thermoelectric materials, yet further thermoelectric figure of merit ZT improvement is largely limited by the inferior electrical transport properties. The established literature on these materials shows only one power factor maximum upon carrier concentration optimization, which is typical for most thermoelectric semiconductors. Surprisingly, we found three power factor maxima when doping Bi with Pb. Based on our first-principles calculations, numerical modeling, and experimental investigation, we attribute the three maxima to the Fermi energy optimization, band convergence, and compositing effect due to in situ formed PbSe precipitates. Consequently, three ZT peaks of 0.9, 1.1, and 1.3 at 873 K are achieved for 4, 10, and 14 at.% Pb-doped samples, respectively, revealing the significance of complex electronic structure and multiple roles of Pb in BiCuSeO. The results establish an accurate band structure characterization for BiCuSeO and identify the role of band convergence and nanoprecipitation as the driving mechanism for high ZT.

8.
Nat Nanotechnol ; 14(7): 691-697, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31011219

RESUMO

Spin waves may constitute key components of low-power spintronic devices. Antiferromagnetic-type spin waves are innately high-speed, stable and dual-polarized. So far, it has remained challenging to excite and manipulate antiferromagnetic-type propagating spin waves. Here, we investigate spin waves in periodic 100-nm-wide stripe domains with alternating upward and downward magnetization in La0.67Sr0.33MnO3 thin films. In addition to ordinary low-frequency modes, a high-frequency mode around 10 GHz is observed and propagates along the stripe domains with a spin-wave dispersion different from the low-frequency mode. Based on a theoretical model that considers two oppositely oriented coupled domains, this high-frequency mode is accounted for as an effective antiferromagnetic spin-wave mode. The spin waves exhibit group velocities of 2.6 km s-1 and propagate even at zero magnetic bias field. An electric current pulse with a density of only 105 A cm-2 can controllably modify the orientation of the stripe domains, which opens up perspectives for reconfigurable magnonic devices.

9.
Nat Commun ; 10(1): 1843, 2019 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-31015446

RESUMO

Understanding the breakdown mechanisms of polymer-based dielectrics is critical to achieving high-density energy storage. Here a comprehensive phase-field model is developed to investigate the electric, thermal, and mechanical effects in the breakdown process of polymer-based dielectrics. High-throughput simulations are performed for the P(VDF-HFP)-based nanocomposites filled with nanoparticles of different properties. Machine learning is conducted on the database from the high-throughput simulations to produce an analytical expression for the breakdown strength, which is verified by targeted experimental measurements and can be used to semiquantitatively predict the breakdown strength of the P(VDF-HFP)-based nanocomposites. The present work provides fundamental insights to the breakdown mechanisms of polymer nanocomposite dielectrics and establishes a powerful theoretical framework of materials design for optimizing their breakdown strength and thus maximizing their energy storage by screening suitable nanofillers. It can potentially be extended to optimize the performances of other types of materials such as thermoelectrics and solid electrolytes.

10.
Adv Sci (Weinh) ; 6(6): 1801931, 2019 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-30937269

RESUMO

Ferroelectric memories are endowed with high data storage density by nanostructure designing, while the robustness is also impaired. For organic ferroelectrics favored by flexible memories, low Curie transition temperature limits their thermal stability. Herein, a ferroelectric random access memory (FeRAM) is demonstrated based on an array of P(VDF-TrFE) lamellae by self-assembly. Written data shows enhanced thermal endurance up to 90 °C and undergoes 12 thermal cycles between 30 and 80 °C with little volatilization. The promoted thermal stability is attributed to pinning effect at interfaces between grain boundaries and lamellae, where charged domain walls and charged defects are coupled. These results provide a strategy for improving robustness of organic flexible FeRAMs, and reveal an attracting coupling effect between different phases of ferroelectric polymer.

11.
Adv Mater ; 31(11): e1806082, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30680811

RESUMO

Polymer-based electrolytes have attracted ever-increasing attention for all-solid-state lithium (Li) metal batteries due to their ionic conductivity, flexibility, and easy assembling into batteries, and are expected to overcome safety issues by replacing flammable liquid electrolytes. However, it is still a critical challenge to effectively block Li dendrite growth and improve the long-term cycling stability of all-solid-state batteries with polymer electrolytes. Here, the interface between novel poly(vinylidene difluoride) (PVDF)-based solid electrolytes and the Li anode is explored via systematical experiments in combination with first-principles calculations, and it is found that an in situ formed nanoscale interface layer with a stable and uniform mosaic structure can suppress Li dendrite growth. Unlike the typical short-circuiting that often occurs in most studied poly(ethylene oxide) systems, this interface layer in the PVDF-based system causes an open-circuiting feature at high current density and thus avoids the risk of over-current. The effective self-suppression of the Li dendrite observed in the PVDF-LiN(SO2 F)2 (LiFSI) system enables over 2000 h cycling of repeated Li plating-stripping at 0.1 mA cm-2 and excellent cycling performance in an all-solid-state LiCoO2 ||Li cell with almost no capacity fade after 200 cycles at 0.15 mA cm-2 at 25 °C. These findings will promote the development of safe all-solid-state Li metal batteries.

12.
ACS Appl Mater Interfaces ; 11(6): 5928-5937, 2019 Feb 13.
Artigo em Inglês | MEDLINE | ID: mdl-30657677

RESUMO

Al-contained Li7- xLa3Zr2- xTa xO12 ( xTa-LLZO) powder was synthesized via solid-state reaction, where increasing the Ta doping level was found to reduce the average particle size and facilitate a higher relative density in the sintered pellet. 0.8Ta-LLZO pellets sintered at 1150 °C achieved a relative density of 96.2 ± 0.2% and survived the Li striping/plating test under a unidirectional current polarization of 0.5 mA/cm2 for more than 8 h without short-circuiting. In contrast, other xTa-LLZO sintered pellets with lower Ta doping levels were short-circuited by lithium dendrites after polarization for much shorter time periods. The microstructure of the sintered body played a more essential role in lithium dendrite prevention compared to relative density alone. By characterizing the microstructure of xTa-LLZO sintered pellets, we proposed a formation mechanism of the pathways for lithium dendrite growth.

13.
ACS Appl Mater Interfaces ; 10(49): 42279-42285, 2018 Dec 12.
Artigo em Inglês | MEDLINE | ID: mdl-30451491

RESUMO

Highly Li-ion conductive Li6PS5Cl solid-state electrolytes (SSEs) were prepared by solid-state sintering method. The influence of sintering temperature and duration on the phase, ionic conductivity, and activation energy of Li6PS5Cl was systematically investigated. The Li6PS5Cl electrolyte with a high ionic conductivity of 3.15 × 10-3 S cm-1 at room temperature (RT) was obtained by sintering at 550 °C for just 10 min, which was more efficient taking into account such a short preparation time in comparison with other reported methods to synthesize Li6PS5Cl SSEs. All-solid-state lithium sulfur batteries (ASSLSBs) based on the Li6PS5Cl SSE were assembled by using the nano-sulfur/multiwall carbon nanotube composite combined with Li6PS5Cl as the cathode and Li-In alloy as the anode. The cell delivered a high discharge capacity of 1850 mAh g-1 at RT for the first full cycle at 0.176 mA cm-2 (∼0.1C). The discharge capacity was 1393 mAh g-1 after 50 cycles. In addition, the Coulombic efficiency remained nearly 100% during galvanostatic cycling. The experimental data showed that Li6PS5Cl was a good candidate for the SSE used in ASSLSBs.

14.
Nat Commun ; 9(1): 3809, 2018 09 18.
Artigo em Inglês | MEDLINE | ID: mdl-30228308

RESUMO

Ferroelectrics, which generate a switchable electric field across the solid-liquid interface, may provide a platform to control chemical reactions (physical properties) using physical fields (chemical stimuli). However, it is challenging to in-situ control such polarization-induced interfacial chemical structure and electric field. Here, we report that construction of chemical bonds at the surface of ferroelectric BiFeO3 in aqueous solution leads to a reversible bulk polarization switching. Combining piezoresponse (electrostatic) force microscopy, X-ray photoelectron spectroscopy, scanning transmission electron microscopy, first-principles calculations and phase-field simulations, we discover that the reversible polarization switching is ascribed to the sufficient formation of polarization-selective chemical bonds at its surface, which decreases the interfacial chemical energy. Therefore, the bulk electrostatic energy can be effectively tuned by H+/OH- concentration. This water-induced ferroelectric switching allows us to construct large-scale type-printing of polarization using green energy and opens up new opportunities for sensing, high-efficient catalysis, and data storage.

15.
Adv Mater ; : e1802902, 2018 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-30109765

RESUMO

The voltage modulation of yttrium iron garnet (YIG) is of practical and theoretical significance; due to its advantages of compactness, high-speed response, and energy efficiency, it can be used for various spintronic applications, including spin-Hall, spin-pumping, and spin-Seebeck effects. In this study, a significant ferromagnetic resonance change is achieved within the YIG/Pt bilayer heterostructures uisng ionic modulation, which is accomplished by modifying the interfacial magnetism in the deposited "capping" platinum layer. With a small voltage bias of 4.5 V, a large ferromagnetic field shift of 690 Oe is achieved in heterostructures of YIG (13 nm)/Pt (3 nm)/(ionic liquid, IL)/(Au capacitor). The remarkable magnetoelectric (ME) tunability comes from the additional and voltage-induced ferromagnetic ordering, caused by uncompensated d-orbital electrons in the Pt metal layer. Confirmed by first-principle calculations, this finding paves the way for novel voltage-tunable YIG-based spintronics.

16.
Nat Nanotechnol ; 13(10): 972, 2018 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30065308

RESUMO

In the version of this Article originally published, the corresponding author names in the author list appeared in the reverse order; they should have read 'Jinxing Zhang and Ce-Wan Nan'. The order of these authors' initials in the 'Correspondence and requests for materials' statement were similarly affected. These errors have now been corrected in all versions of the Article.

17.
Dalton Trans ; 47(35): 12337-12344, 2018 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-30117509

RESUMO

Based on the existing calculation reports, sulfur doping is an effective approach to alleviate the structure collapse of Li2MnSiO4 during cycling. Herein, we investigate the feasibility and limitations of S doping in Li2MnSiO4 by experiment. In our work, the solid solubility of S is confirmed and exceeding the threshold results in MnS impurity. The existence state and site of the S element in a Li2MnSiO4 crystal structure is also confirmed. It is found that S doping significantly improves the structural reversibility and cycling stability. Compared with a pristine sample, a 1mol% S doped sample exhibits a much higher initial coulombic efficiency (88.3%), excellent capacity retention (98% at 10th cycles for instance) and enhanced rate performance. Moreover, the 1mol% S doped sample can retain a discharge capacity of 137 mA h g-1 after 30 cycles while the pristine sample only has 61.6 mA h g-1. This study confirms the effectivity of S doping in suppressing the structural distortion in Li2MnSiO4.

18.
ACS Appl Mater Interfaces ; 10(29): 24791-24798, 2018 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-29972294

RESUMO

Solid electrolytes with high ionic conductivity and good mechanical properties are required for solid-state lithium-ion batteries. In this work, we synthesized composite polymer electrolytes (CPEs) with a three-dimensional (3D) Li0.33La0.557TiO3 (LLTO) network as a nano-backbone in poly(ethylene oxide) matrix by hot-pressing and quenching. Self-standing 3D-CPE membranes were obtained with the support of the LLTO nano-backbone. These membranes had much better thermal stability and enhanced mechanical strength in comparison with solid polymer electrolytes. The influence of lithium (Li) salt concentration on the conductivity of 3D-CPEs was systematically studied, and an ionic conductivity as high as 1.8 × 10-4 S·cm-1 was achieved at room temperature. The electrochemical window of the 3D-CPEs was 4.5 V vs Li/Li+. More importantly, the 3D-CPE membranes could suppress the growth of Li dendrite and reduce polarization; therefore, a symmetric Li|3D-CPE|Li cell with these membranes was cycled at a current density of 0.1 mA·cm-2 for over 800 h. All of the superior properties above made the 3D-CPEs with the LLTO nano-backbone a promising electrolyte candidate for flexible solid-state lithium-ion batteries.

19.
Nat Nanotechnol ; 13(10): 947-952, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30038370

RESUMO

Charged domain walls in ferroelectrics exhibit a quasi-two-dimensional conduction path coupled to the surrounding polarization. They have been proposed for use as non-volatile memory with non-destructive operation and ultralow energy consumption. Yet the evolution of domain walls during polarization switching makes it challenging to control their location and conductance precisely, a prerequisite for controlled read-write schemes and for integration in scalable memory devices. Here, we explore and reversibly switch the polarization of square BiFeO3 nanoislands in a self-assembled array. Each island confines cross-shaped, charged domain walls in a centre-type domain. Electrostatic and geometric boundary conditions induce two stable domain configurations: centre-convergent and centre-divergent. We switch the polarization deterministically back and forth between these two states, which alters the domain wall conductance by three orders of magnitude, while the position of the domain wall remains static because of its confinement within the BiFeO3 islands.

20.
Inorg Chem ; 57(10): 6051-6056, 2018 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-29722989

RESUMO

The quaternary compound Cu2ZnSnSe4 (CZTSe), as a typical candidate for both solar cells and thermoelectrics, is of great interest for energy harvesting applications. Materials with a high thermoelectric efficiency have a relatively low thermal conductivity, which is closely related to their chemical bonding and lattice dynamics. Therefore, it is essential to investigate the lattice dynamics of materials to further improve their thermoelectric efficiency. Here we report a lattice dynamic study in a cobalt-substituted CZTSe system using temperature-dependent X-ray absorption fine structure spectroscopy (TXAFS). The lattice contribution to the thermal conductivity is dominant, and its reduction is mainly ascribed to the increment of point defects after cobalt substitution. Furthermore, a lattice dynamic study shows that the Einstein temperature of atomic pairs is reduced after cobalt substitution, revealing that increasing local structure disorder and weakened bonding for each of the atomic pairs are achieved, which gives us a new perspective for understanding the behavior of lattice thermal conductivity.

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