Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy-Yb): A Family of Rare-Earth-Based Layered Triangular Lattice Magnets.

The exploration of new rare-earth (RE)-based triangular-lattice materials plays a significant role in motivating the discovery of exotic magnetic states. Herein, we report a family of hexagonal perovskite compounds Ba6RE2Ti4O17 (RE = Nd, Sm, Gd, Dy-Yb) with a space group of P63/mmc, where magnetic RE3+ ions are distributed on the parallel triangular-lattice layers within the ab-plane and stacked in an 'AA'-type fashion along the c-axis. The low-temperature magnetic characterizations indicate that all synthesized Ba6RE2Ti4O17 compounds exhibit dominant antiferromagnetic (AFM) interactions and the absence of magnetic order down to 1.8 K. The isothermal magnetization and electron spin resonance results reveal the distinct magnetic anisotropy for the compounds with different RE ions. Moreover, the as-grown Ba6Nd2Ti4O17 single crystals exhibit Ising-like magnetic anisotropy with a magnetic easy-axis perpendicular to the triangle-lattice plane and no long-range magnetic order down to 80 mK, as the quantum spin liquid candidate with dominant Ising-type interactions.

Nanoporous Au-Ag shell with fast kinetics: integrating chemical and plasmonic catalysis.

Nanoporous noble metals and alloys are widely utilized as efficient catalysts, because they have high surface-to-volume ratios for sufficient active sites and induce molecule polarization through plasmon excitation as well. Herein, we demonstrate one approach to fabricate nanoporous Au-Ag shell. Such material represents the dual functions serving as efficient catalysts and high-performance surface-enhanced Raman scattering substrate. In situ spectrum acquisition can track the conversion of p-nitrothiophenol to 4, 4'-dimercapto-azobenzene at ambient temperature. In particular, as a result of chemical catalysis of Ag elements and strong plasmon-molecule coupling, catalytic kinetics of nanoporous Au-Ag shell is 79.2-123.8 times faster than Au nanoparticles (NPs), and 2.2-3.3 times faster than Ag NPs. This investigation offers a route to design superior catalysts to integrate chemical and plasmonic catalysis.

Electrochemical Biosensor Based on Nanoporous Au/CoO Core-Shell Material with Synergistic Catalysis.

An ultrathin CoO layer is deposited on the skeleton surfaces of a nanoporous gold (NPG) film by using atomic layer deposition, creating a flexible electrode. Detailed characterization demonstrates the superior performance of the flexible NPG/CoO hybrids for electrochemical catalysis. The NPG/CoO hybrid not only achieves high catalytic activity for glucose oxidation and H2O2 reduction, but also exhibits a linear dependence of the electrical signal on the concentration of glucose and H2O2 molecules in the electrolyte. Meanwhile, the sensitivity for H2O2 reduction can be as high as 62.5 µA mm(-1) cm(-2) with linear dependence on the concentration in the range of 0.1-92.9 mm. The high sensitivity is proposed to result from the synergistic effect of Au and CoO at the interfaces, and the high conductivity of the gold skeleton with a large surface area. The superior electrochemical performance of this hybrid electrode is promising for future potential applications in various transitional-metal-oxide-based electrochemical electrodes.

Topography-specific isotropic tunneling in nanoparticle monolayer with sub-nm scale crevices.

Material used in flexible devices may experience anisotropic strain with identical magnitude, outputting coherent signals that tend to have a serious impact on device reliability. In this work, the surface topography of the nanoparticles (NPs) is proposed to be a parameter to control the performance of strain gauge based on tunneling behavior. In contrast to anisotropic tunneling in a monolayer of spherical NPs, electron tunneling in a monolayer of urchin-like NPs actually exhibits a nearly isotropic response to strain with different loading orientations. Isotropic tunneling of the urchin-like NPs is caused by the interlocked pikes of these urchin-like NPs in a random manner during external mechanical stimulus. Topography-dependent isotropic tunneling in two dimensions reported here opens a new opportunity to create highly reliable electronics with superior performance.

Single-Phase Ternary Compounds with a Disordered Lattice and Liquid Metal Phase for High-Performance Li-Ion Battery Anodes.

Si is considered as the promising anode materials for lithium-ion batteries (LIBs) owing to their high capacities of 4200 mAh g-1 and natural abundancy. However, severe electrode pulverization and poor electronic and Li-ionic conductivities hinder their practical applications. To resolve the afore-mentioned problems, we first demonstrate a cation-mixed disordered lattice and unique Li storage mechanism of single-phase ternary GaSiP2 compound, where the liquid metallic Ga and highly reactive P are incorporated into Si through a ball milling method. As confirmed by experimental and theoretical analyses, the introduced Ga and P enables to achieve the stronger resistance against volume variation and metallic conductivity, respectively, while the cation-mixed lattice provides the faster Li-ionic diffusion capability than those of the parent GaP and Si phases. The resulting GaSiP2 electrodes delivered the high specific capacity of 1615 mAh g-1 and high initial Coulombic efficiency of 91%, while the graphite-modified GaSiP2 (GaSiP2@C) achieved 83% of capacity retention after 900 cycles and high-rate capacity of 800 at 10,000 mA g-1. Furthermore, the LiNi0.8Co0.1Mn0.1O2//GaSiP2@C full cells achieved the high specific capacity of 1049 mAh g-1 after 100 cycles, paving a way for the rational design of high-performance LIB anode materials.

Lattice Strain Mediated Reversible Reconstruction in CoMoO4·0.69H2O for Intermittent Oxygen Evolution.

A heterogeneous interface usually plays a versatile role in modulating catalysis and the durability of hybrid electrocatalysts for oxygen evolution reaction (OER), and its intrinsic mechanism is still in dispute due to an uncertain correlation of initial, intermediate and active phases. In this article, the CoMoO4·0.69H2O/Co3O4 heterogeneous interface is configured to understand the evolution kinetics of these correlated phases. Due to the chemically and electrochemically "inert" character of Co3O4 support, lattice strain with 3.31% tuning magnitude in primary CoMoO4·0.69H2O can be inherited after spontaneous dissolution of molybdenum cations in electrolyte, dominating catalytic activity of the reconstructed CoOOH. In situ Raman spectroscopy demonstrates reversible conversion between active CoOOH and amorphous cobalt oxide during OER when positive and negative potentials are sequentially supplied onto hybrid catalysts with favorable strain. Therefore, superior durability with negligible decay after 10 cycles is experimentally identified for intermittent oxygen evolution. Theoretical calculations indicate that appropriate stress within the electrocatalyst could reduce the reaction energy barrier and enhance the OER performance by optimizing the adsorption of intermediates.

Shubnikov-de Haas oscillations and nontrivial topological states in Weyl semimetal candidate SmAlSi.

The RAlX (R = Light rare earth; X = Ge, Si) compounds, as a family of magnetic Weyl semimetal, have recently attracted growing attention due to the tunability of Weyl nodes and its interactions with diverse magnetism by rare-earth atoms. Here, we report the magnetotransport evidence and electronic structure calculations on nontrivial band topology of SmAlSi, a new member of this family. At low temperatures, SmAlSi exhibits large non-saturated magnetoresistance (MR) (as large as ∼5500% at 2 K and 48 T) and distinct Shubnikov-de Haas (SdH) oscillations. The field dependent MRs at 2 K deviate from the semiclassical (µ0H)2variation but follow the power-law relation MR∝(µ0H)mwith a crossover fromm∼ 1.52 at low fields (µ0H< 15 T) tom∼ 1 under high fields (µ0H> 18 T), which is attributed to the existence of Weyl points and electron-hole compensated characteristics with high mobility. From the analysis of SdH oscillations, two fundamental frequencies originating from the Fermi surface pockets with non-trivialπBerry phases and small cyclotron mass can be identified, this feature is supported by the calculated electronic band structures with two Weyl pockets near the Fermi level. Our study establishes SmAlSi as a paradigm for researching the novel topological states of RAlX family.

The effect of carrier doping on magnetism and electronic behavior in double perovskite La2ZnIrO6.

Tuning of spin-orbit coupling and electron correlation effects in iridates by introducing electron or hole carriers can produce interesting physical phenomena. In this work, we experimentally investigate the electron/hole doping effect on magnetism and electrical transport in the canted antiferromagnetic (AFM) double perovskite La2ZnIrO6, where hole/electron doping are realized in two serial La2Zn1-x Li x IrO6 (0 ⩽ x ⩽ 0.35) and La2Zn1-y Ga y IrO6 (0 ⩽ y  ⩽ 0.3) compounds, respectively. The x-ray photoelectron spectroscopy (XPS) reveals the existence of Ir5+ and Ir3+ oxide states in the Li+ and Ga3+ doped La2ZnIrO6. The magnetic susceptibilities and electron spin resonance (ESR) results reveal different responses between the Ir5+(5d4) and Ir3+ (5d6) ions in doped La2ZnIrO6, the Ir5+ ions have Van-Vleck paramagnetic contribution contrast to the completely nonmagnetic Ir3+ ions. Moreover, the Li+ doping cause more dramatic suppression of transition temperature (T N) and net ferromagnetic (FM) moments. All the Li+/Ga3+ doped samples remain Mott insulating state well fitted by the variable-range-hopping (VRH) transport mechanism. As a comparison, hole-doping is more effective to enhance the electrical conductivity than the case of electron, suggesting possible asymmetry of density of states nearby the Fermi level.

A comparative study on magnetic order and field-induced magnetic transition in double perovskite iridates: RE2ZnIrO6 and RE2MgIrO6 (RE = Pr, Nd, Sm, Eu, Gd).

We perform a comparative magnetic study on two series of rare-earth (RE) based double perovskite iridates RE2BIrO6 (RE = Pr, Nd, Sm-Gd; B = Zn, Mg), which show Mott insulating state with tunable charge energy gap from ∼330 meV to ∼560 meV by changing RE cations. For nonmagnetic RE = Eu cations, Eu2MgIrO6 shows antiferromagnetic (AFM) order and field-induced spin-flop transitions below Néel temperature (T N) in comparison with the ferromagnetic (FM)-like behaviors of Eu2ZnIrO6 at low temperatures. For magnetic-moment-containing RE ions, Gd2BIrO6 show contrasting magnetic behaviors with FM-like transition (B = Zn) and AFM order (B = Mg), respectively. While, for RE = Pr, Nd and Sm ions, all members show AFM ground state and field-induced spin-flop transitions below T N irrespective of B = Zn or Mg cations. Moreover, two successive field-induced metamagnetic transitions are observed for RE2ZnIrO6 (RE = Pr, Nd) in high field up to 56 T, the resultant field temperature (H-T) phase diagrams are constructed. The diverse magnetic behaviors in RE2BIrO6 reveal that the 4f-Ir exchange interactions between the RE and Ir sublattices can mediate their magnetism.

Bioinspired, Spine-Like, Flexible, Rechargeable Lithium-Ion Batteries with High Energy Density.

The rapid development of flexible and wearable electronics proposes the persistent requirements of high-performance flexible batteries. Much progress has been achieved recently, but how to obtain remarkable flexibility and high energy density simultaneously remains a great challenge. Here, a facile and scalable approach to fabricate spine-like flexible lithium-ion batteries is reported. A thick, rigid segment to store energy through winding the electrodes corresponds to the vertebra of animals, while a thin, unwound, and flexible part acts as marrow to interconnect all vertebra-like stacks together, providing excellent flexibility for the whole battery. As the volume of the rigid electrode part is significantly larger than the flexible interconnection, the energy density of such a flexible battery can be over 85% of that in conventional packing. A nonoptimized flexible cell with an energy density of 242 Wh L-1 is demonstrated with packaging considered, which is 86.1% of a standard prismatic cell using the same components. The cell also successfully survives a harsh dynamic mechanical load test due to this rational bioinspired design. Mechanical simulation results uncover the underlying mechanism: the maximum strain in the reported design (≈0.08%) is markedly smaller than traditional stacked cells (≈1.1%). This new approach offers great promise for applications in flexible devices.

N,S co-doped carbon dots as a stable bio-imaging probe for detection of intracellular temperature and tetracycline.

Stable bioimaging with nanomaterials in living cells has been a great challenge and of great importance for understanding intracellular events and elucidating various biological phenomena. Herein, we demonstrate that N,S co-doped carbon dots (N,S-CDs) produced by one-pot reflux treatment of C3N3S3 with ethane diamine at a relatively low temperature (80 °C) exhibit a high fluorescence quantum yield of about 30.4%, favorable biocompatibility, low-toxicity, strong resistance to photobleaching and good stability. The N,S-CDs as an effective temperature indicator exhibit good temperature-dependent fluorescence with a sensational linear response from 20 to 80 °C. In addition, the obtained N,S-CDs facilitate high selectivity detection of tetracycline (TC) with a detection limit as low as 3 × 10-10 M and a wide linear range from 1.39 × 10-5 to 1.39 × 10-9 M. More importantly, the N,S-CDs display an unambiguous bioimaging ability in the detection of intracellular temperature and TC with satisfactory results.

Hierarchical nanoporous gold-platinum with heterogeneous interfaces for methanol electrooxidation.

The electrocatalysts utilized as the prospective electrodes in fuel cells and high efficient energy conversion devices require both the interconnected channels for efficient electrolyte transportation and the superior catalytic activity with long service life. In this work, nanoporous gold with the rigid skeletons in three dimensions is partially decorated by porous platinum shell containing nanoscale interstitials, aiming to create the heterogeneous gold-platinum interfaces and facilitate the electrolyte transportation as well. In comparison with no catalytic activity of bare nanoporous gold, the catalytic activity of hierarchical nanoporous gold-platinum towards electrochemical oxidation of methanol increases with the loading level of platinum shells, resulting in the highest electrochemical area of 70.4 m(2)·g(-1) after the normalization by the mass of platinum. Heterogeneous gold-platinum interfaces affect the tolerance of the absorbed intermediate species because of the oxidization by the oxygenated species absorbed on the gold surface and the enhanced ion transportation within the porous platinum shell.

Electrical conduction of nanoparticle monolayer for accurate tracking of mechanical stimulus in finger touch sensing.

A flexible strain gauge is an essential component in advanced human-machine interfacing, especially when it comes to many important mobile and biomedical appliances that require the detection of finger touches. In this paper, we report one such strain gauge made from a strip of nanoparticle monolayer onto a flexible substrate. This proposed gauge operates on the observation that there is a linear relationship between electrical conduction and mechanical displacement in a compressive state. Due to its prompt temporal response, the gauge can accurately track various mechanical stimuli running at the frequencies of interest. Experiments have confirmed that the proposed strain gauge has a strain detection limit as low as 9.4 × 10(-5), and its gauge factor can be as large as 70, making this device particularly suitable for sensitive finger touch sensing. Furthermore, negligible degradation in the gauge's output electrical signal is observed even after 9000 loading/unloading cycles.

Polarization enhancement and ferroelectric switching enabled by interacting magnetic structures in DyMnO3 thin films.

The mutual controls of ferroelectricity and magnetism are stepping towards practical applications proposed for quite a few promising devices in which multiferroic thin films are involved. Although ferroelectricity stemming from specific spiral spin ordering has been reported in highly distorted bulk perovskite manganites, the existence of magnetically induced ferroelectricity in the corresponding thin films remains an unresolved issue, which unfortunately halts this step. In this work, we report magnetically induced electric polarization and its remarkable response to magnetic field (an enhancement of ~800% upon a field of 2 Tesla at 2 K) in DyMnO3 thin films grown on Nb-SrTiO3 substrates. Accompanying with the large polarization enhancement, the ferroelectric coercivity corresponding to the magnetic chirality switching field is significantly increased. A picture based on coupled multicomponent magnetic structures is proposed to understand these features. Moreover, different magnetic anisotropy related to strain-suppressed GdFeO3-type distortion and Jahn-Teller effect is identified in the films.