As a generic property, all substances transfer heat through microscopic collisions of constituent particles . A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations. As a result, a solid is usually thermally more conductive than a liquid. In canonical viewpoints, such a difference also serves as the dynamic signature distinguishing a solid from a liquid. Here, we report liquid-like thermal conduction observed in the crystalline AgCrSe. The transverse acoustic phonons are completely suppressed by the ultrafast dynamic disorder while the longitudinal acoustic phonons are strongly scattered but survive, and are thus responsible for the intrinsically ultralow thermal conductivity. This scenario is applicable to a wide variety of layered compounds with heavy intercalants in the van der Waals gaps, manifesting a broad implication on suppressing thermal conduction. These microscopic insights might reshape the fundamental understanding on thermal transport properties of matter and open up a general opportunity to optimize performances of thermoelectrics.

5393www.MaterialsViews.com wileyonlinelibrary.com environment. [ 9,10 ] Recently, due to the deepening cognition of the intrinsic and extrinsic GMR effect, growing attention has been paid to polycrystalline manganites to obtain the extrinsic low-fi eld magnetoresistance (LFMR) by structuring grain boundaries, nanosized inclusions, interface phase, and artifi cial grain boundaries. What's more, the LFMR in composites or fi lms can be further improved by introducing a secondary phase (usually non-magnetic or antiferromagnetic insulators). [11][12][13][14][15][16][17][18][19][20] For example, the LFMR values of -6% at 5 K and 0.16 T in LSMO:SrTiO 3 superlattice structure, [ 3 ] -17.5% at 30 K and 1 T in LSMO:ZnO columnar structure, [ 21 ] -8% at 10-150 K and 1 T in LSMO:MgO nanorod arrays structure [ 22 ] and -12% at 77 K and 0.4 T in LSMO:Ag 0-3 structure [ 23 ] have been reported. However, neither the early results obtained from LSMO polycrystalline fi lms [ 24 ] or recent results obtained from LSMO:ZnO composite fi lms with a columnar structure, [ 21 ] enhanced LFMR values are always display in a low temperature range. That may be due to the large grain size in polycrystalline fi lms (≈µm) or weak spin coupling at the phase boundaries in the composite thin fi lms. Systems featuring a large LFMR at temperatures close to or even higher than room temperature are also interesting owing to their potential applications in magnetic fi eld sensing and data storage. [ 25 ] Dey et al. have found that the large LFMR will keep steady in a higher temperature range when the grain size is in nanoscale and gets pronounced with the decrease in particle size. [ 26 ] It is notable that the spin pinned effect occurs at the nanosized grain surface defect sites or spin coupling at the boundaries. [ 26,27 ] In addition, the short range ferromagnetic (FM) coupling order may add the opportunity of spin scattering even near the Curie temperature. [ 28,29 ] Thus it is speculated that the high-temperature LFMR in LSMO composite fi lms can be got through tuning the grain size and the FM coupling at the phase boundary. MacManus-Driscoll et al. proposed that the self-assembled composite fi lms are free from substrate clamping constraints and form strained vertical interface areas which can be used to tune the FM coupling by another phase and also can provide a more fl exible way to control the growth of the fi lms which can be used to control the grain size to get enhanced physical properties. [ 30 ] To prepare the LSMO-based composite fi lms, on the one hand, it should NiO nano composite thin fi lms, which will be expected to be applied in the devices using for a wide temperature range.

Discovering efficient and promising non-noble catalysts toward the alkaline hydrogen evolution reaction (HER) is vital for a clean energy system. Here, we design an efficient alkaline HER electrocatalyst, coating of WN nanowire core with a Ni­(OH)2 shell supported on a carbon fiber paper (WN-Ni­(OH)2). In a 1 M KOH solution, the hierarchical electrocatalyst affords a current density of 20 mA cm–2 at an overpotential of 170 mV and 100 mA cm–2 at 245 mV. The enhanced performance of WN-Ni­(OH)2 in the HER is attributed to the synergy between WN and Ni­(OH)2: during water dissociation, hydroxyl groups are preferentially adsorbed on WN and hydrogen on Ni­(OH)2; meanwhile, Ni­(OH)2 could promote hydroxyl group desorption from WN. Thus, the full-surface Volmer reaction kinetics could be enhanced. As a consequence, the WN-Ni­(OH)2 has a reduced activation energy of the HER and enhanced intrinsic activity performance. Meanwhile, the hybrid can reach a current density of 100 mA cm–2 at an overpotential of 339 mV for the oxygen evolution reaction (OER), and an overpotential of 510 mV for the full water-splitting reaction. This interfacial cooperation offers a promising bifunctional electrocatalyst, as well as a hopeful strategy for fabricating efficient nitride-based electrocatalysts in alkaline media.

A large magnetic coupling has been observed at the La0.7Ca0.3MnO3/LaNiO3 (LCMO/LNO) interface. The x-ray photoelectron spectroscopy (XPS) study results show that Fermi level continuously shifted across the LCMO/LNO interface in the interface region. In addition, the charge transfer between Mn and Ni ions of the type Mn3+ − Ni3+ → Mn4+ − Ni2+ with the oxygen vacancies are observed in the interface region. The intrinsic interfacial charge transfer can give rise to itinerant electrons, which results in a “shoulder feature” observed at the low binding energy in the Mn 2p core level spectra. Meanwhile, the orbital reconstruction can be mapped according to the Fermi level position and the charge transfer mode. It can be considered that the ferromagnetic interaction between Ni2+ and Mn4+ gives rise to magnetic regions that pin the ferromagnetic LCMO and cause magnetic coupling at the LCMO/LNO interface.

Ethylene/polar monomer coordination copolymerization offers an attractive way of making functionalized polyolefins. However, ethylene copolymerization with industrially relevant short chain length alkenoic acid remain a big challenge. Here we report the efficient direct copolymerization of ethylene with vinyl acetic acid by tetranuclear nickel complexes. The protic monomer can be extended to acrylic acid, allylacetic acid, ω-alkenoic acid, allyl alcohol, and homoallyl alcohol. Based on X-ray analysis of precatalysts, control experiments, solvent-assisted electrospray ionization-mass spectrometry detection of key catalytic intermediates, and density functional theory studies, we propose a possible mechanistic scenario that involves a distinctive vinyl acetic acid enchainment enabled by Ni···Ni synergistic effects. Inspired by the mechanistic insights, binuclear nickel catalysts are designed and proved much more efficient for the copolymerization of ethylene with vinyl acetic acid or acrylic acid, achieving the highest turnover frequencies so far for both ethylene and polar monomers simultaneously.