Atomic-resolution Interfacial Microstructure and Thermo-electro-magnetic Energy Conversion Performance of Gd/Bi_(0.5)Sb_(1.5)Te_(3)Composites

Thermo-electro-magnetic materials with simultaneously large magnetocaloric(MC)and thermoelectric(TE)effects are the core part for designing TE/MC all-solid-state cooling devices.Compositing MC phase with TE material is an effective approach.However,the elemental diffusion and chemical reaction occurring at the two-phase interfaces could significantly impair the cooling performance.Herein,Gd/Bi_(0.5)Sb_(1.5)Te_(3)(Gd/BST)composites were prepared by a low-temperature high-pressure spark plasma sintering method with an aim to control the extent of interfacial reaction.The reaction of Gd with the diffusive Te and the formation of GdTe nanocrystals were identified at the Gd/BST interfaces by the atomic-resolution microscope.The formed Bi’_(Te)antisite defects and enhanced{000 l}preferential orientation in BST are responsible for the increased carrier concentration and mobility,which leads to optimized electrical properties.The heterogeneous interface phases,along with antisite defects,favor the phonon scattering enhancement and lattice thermal conductivity suppression.The optimized composite sintered at 693 K exhibited a maximum ZT of 1.27 at 300 K.Furthermore,the well-controlled interfacial reaction has a slight impact on the magnetic properties of Gd and a high magnetic entropy change is retained in the composites.This work provides a universal approach to fabricating thermo-electro-magnetic materials with excellent MC and TE properties.

Enhanced Electrical Properties of Bi_(2−x)Sb_(x)Te_(3) Nanoflake Thin Films Through Interface Engineering

The structure–property relationship at interfaces is difficult to probe for thermoelectric materials with a complex interfacial microstructure.Designing thermoelectric materials with a simple,structurally-uniform interface provides a facile way to understand how these interfaces influence the transport properties.Here,we synthesized Bi_(2−x)Sb_(x)Te_(3)(x=0,0.1,0.2,0.4)nanoflakes using a hydrothermal method,and prepared Bi_(2−x)Sb_(x)Te_(3) thin films with predominantly(0001)interfaces by stacking the nanoflakes through spin coating.The influence of the annealing temperature and Sb content on the(0001)interface structure was systematically investigated at atomic scale using aberration-corrected scanning transmission electron microscopy.Annealing and Sb doping facilitate atom diffusion and migration between adjacent nanoflakes along the(0001)interface.As such it enhances interfacial connectivity and improves the electrical transport properties.Interfac reactions create new interfaces that increase the scattering and the Seebeck coefficient.Due to the simultaneous optimization of electrical conductivity and Seebeck coefficient,the maximum power factor of the Bi_(1.8)Sb_(0.2)Te_(3) nanoflake films reaches 1.72 mW m^(−1)K^(−2),which is 43%higher than that of a pure Bi_(2)Te_(3) thin film.

Notes in accordions-organized MXene equipped with CeO_(2) for synergistically adsorbing and catalyzing polysulfides for high-performance lithium-sulfur batteries

Limited by the shuttle effect, the application of lithium-sulfur batteries is not impressive. As an organ layered two-dimensional(2D) material, MXene has a great electrical conductivity and high specific surface area. Meanwhile, the introduction of metal oxides can restrain the shuttle effect. Hence, this paper prepared CeO_(2)/MXene as a cathode material of Li-S batteries. Ce and Ti can chemically adsorb S, and the interlayer structure of MXene can limit S while the interlayer space can alleviate volume expansion.The discharge capacity at 0.5 C is as high as 1051.1 m Ah g^(-1), and 921.9 m Ah g^(-1) after 200 cycles. The average coulombic efficiency is 97.75%. The organized MXene with CeO_(2) like notes in accordions are new efficient materials for lithium-sulfur batteries.

A Charge Equalizer in Accordion-MXene-Modified Layer Leading to Spherical Lithium Deposition

Lithium-ion batteries with polymer electrolytes(PEs)are promising candidates for high safety performance batteries.However,conventional PEs suffer from poor compatibility and high impedance of electrolyte-electrode interfaces.Herein,we present a method of the interfacial modification for PEs to inhibit lithium dendrites based on the solution to the interfacial compatibility.Our strategy is to improve the interfacial properties and inhibit the dendrite generation by coating a modified layer on PEs of the anode side with acetylene black(AB)and MXene.The mixed conductive layer(MCL)can promote the generation of Li3N and LiF with a uniform arrangement of electrons to form a dense solid electrolyte interphase layer and the even lithium-ion deposition for improving the performance and stability of the battery during cycling.After adding the MCL,the discharge capacity of solid lithium-ion batteries(SLIBs)with lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)/organic modified montmorillonite(OMMT)/soybean isolate protein(SPI)/poly(vinylidene fluoride)(PVDF)(LOSP)PE from 74.2 mAh g^(-1)up to 111.1 mAh g^(-1)(AB-LiTFSI/OMMT/SPI/PVDF(AB-LOSP))and 111.6 mAh g^(-1)(AB/MXene-LiTFSI/OMMT/SPI/PVDF(AB/MXene-LOSP)).The polarization voltage dropped by 0.06 and 0.12 V,respectively.This work represents a milestone in the dendrite-free SLIBs with good performances.

Enhanced thermoelectric performance and atomic-resolution interfacial structures in BiSbTe thermo-electro-magnetic nanocomposites incorporating magnetocaloric LaFeSi nanoparticles

Incorporating magnetic nanoparticles in thermoelectric(TE)materials introduce magnetic interfaces with additional electron and phonon scattering mechanism for high TE performance.However,the influence of heterogeneous interfaces between magnetic nanoparticles and TE matrix on electronic and thermal transport remains elusive in the thermo-electric-magnetic nanocomposites.Here,using p-type TE material Bi_(0.3)Sb_(1.7)Te_(3)(BST)as matrix and magnetocaloric(MC)material La(Fe_(0.92)Co_(0.08))_(11.9)Si_(1.1)(LFS)nanoparticles as a second phase,TE/MC nanocomposites xLFS/BST(x=0.1%,0.2%,0.3% and 0.4%)were synthesized using spark plasma sintering method.The atomic-resolution interfacial structures demonstrate that Te vacancies originating from LFS-BST interfacial reaction decreases the hole concentration of the LFS/BST nanocomposites and enhances the Seebeck coefficient.The LFS/BST nanocomposites exhibit lower thermal conductivity due to enhanced phonon scattering by interfaces and defects.All the nanocomposites have higher ZT than BST matrix,with 0.2% LFS/BST nanocomposite achieving highest ZT=1.11 at 380 K.At working current 1.4 A,the device fabricated using 0.2% LFS/BST nanocomposite achieves maximal cooling temperature 4.9 K,which is 58% higher than the matrix.Moreover,the MC properties are retained in all the nanocomposites,which make them a promising candidate to achieve high TE performance and dual TE/MC properties for future applications.

Magneto-enhanced electro-thermal conversion performance

Synergistically regulating carrier and phonon transport on the nanoscale is extremely difficult for all thermoelectric(TE)materials without cage structures.Herein BaFe_(12)O_(19)/Bi_(2)Te_(2.5)Se_(0.5)thermoelectromagnetic nanocomposites are designed and synthesized as a benchmarking example to simultaneously tailor the transport properties on the nanoscale.A magneto-trapped carrier effect induced by BaFe_(12)O_(19)hard-magnetic nanoparticles(NPs)is discovered,which can lower the carrier concentration of n-type Bi_(2)Te_(2.5)Se_(0.5)matrix by 16%,and increase the Seebeck coefficient by 16%.Meanwhile,BaFe_(12)O_(19)NPs provide phonon scattering centers and reduce the thermal conductivity by 12%.As a result,the ZT value of the nanocomposites is enhanced by more than 25%in the range of 300-450 K,and the cooling temperature difference increases by 65%near room temperature.This work greatly broadens the commercial application potential of ntype Bi_(2)Te_(2.5)Se_(0.5),and demonstrates magneto-trapped carrier effect as a universal strategy to enhance the electro-thermal conversion performance of TE materials with high carrier concentration.

Atomic defects,functional groups and properties in MXenes

MXenes,a new family of functional two-dimensional(2 D) materials,have shown great potential for an extensive variety of applications within the last decade.Atomic defects and functional groups in MXenes are known to have a tremendous influence on the functional properties.In this review,we focus on recent progress in the characterization of atomic defects and functional group chemistry in MXenes,and how to control them to directly influence various properties(e.g.,electron transport,Li^(+) adsorption,hydrogen evolution reaction(HER) activity,and magnetism) of 2 D MXenes materials.Dynamic structural transformations such as oxidation and growth induced by atomic defects in MXenes are also discussed.The review thus provides perspectives on property optimization through atomic defect engineering,and bottom-up synthesis methods based on defect-assisted homoepitaxial growth of MXenes.

Boosting in-plane anisotropy by periodic phase engineering in two-dimensional VO_(2) single crystals

In-plane anisotropy(IPA)due to asymmetry in lattice structures provides an additional parameter for the precise tuning of characteristic polarization-dependent properties in two-dimensional(2D)materials,but the narrow range within which such method can modulate properties hinders significant development of related devices.Herein we present a novel periodic phase engineering strategy that can remarkably enhance the intrinsic IPA obtainable from minor variations in asymmetric structures.By introducing alternant monoclinic and rutile phases in 2D VO_(2)single crystals through the regulation of interfacial thermal strain,the IPA in electrical conductivity can be reversibly modulated in a range spanning two orders of magnitude,reaching an unprecedented IPA of 113.Such an intriguing local phase engineering in 2D materials can be well depicted and predicted by a theoretical model consisting of phase transformation,thermal expansion,and friction force at the interface,creating a frame-work applicable to other 2D materials.Ultimately,the considerable adjustability and reversibility of the presented strategy provide opportunities for future polarization-dependent photoelectric and optoelectronic devices.