Single-atom catalysts (SACs) have demonstrated superior catalytic performance in numerous heterogeneous reactions. However, producing thermally stable SACs, especially in a simple and scalable way, remains a formidable challenge. Here, we report the synthesis of Ru SACs from commercial RuO 2 powders by physical mixing of sub-micron RuO 2 aggregates with a MgAl 1.2 Fe 0.8 O 4 spinel. Atomically dispersed Ru is confirmed by aberration-corrected scanning transmission electron microscopy and X-ray absorption spectroscopy. Detailed studies reveal that the dispersion process does not arise from a gas atom trapping mechanism, but rather from anti-Ostwald ripening promoted by a strong covalent metalsupport interaction. This synthetic strategy is simple and amenable to the large-scale manufacture of thermally stable SACs for industrial applications.

We have calculated the electronic structures of five different manganese-oxo dimer complexes using density functional methods combined with the broken symmetry and spin projection concepts. The number of carboxylate, oxo, and peroxo bridging ligands was varied, and the terminal ligands were triazacyclononane (TACN). The formal Mn oxidation states varied from Mn(III)(2) and Mn(III)Mn(IV) to Mn(IV)(2). These complexes have been synthesized and their X-ray structures and magnetic properties measured previously. We have calculated the Heisenberg spin coupling parameters J and resonance delocalization parameters B for all of these systems. Despite the very small energy differences involved, there is a good correspondence between calculated and experimental Heisenberg J parameters. We have analyzed potential changes in the calculated effective Heisenberg coupling J(eff) for the mixed-valence Mn(III)Mn(IV) complexes when partial or complete delocalization due to the B parameter is taken into account. These changes depend also on the energy of the relevant intervalence band. Surprisingly, in the two mixed-valence systems studied, the high spin S = (5)/(2) state lies below S = (7)/(2). This is consistent with spin coupling between Mn with site spins S(1) = 1, S(2) = (3)/(2), corresponding to intermediate spin Mn(I) and Mn(II) respectively, instead of the coupling expected from the formal oxidation states, S(1) = 2, S(2) = (3)/(2) from high spin Mn(III) and Mn(IV). The spin and charge distributions in the broken symmetry ground states are also consistent with intermediate spin S(1) = 1, S(2) = (3)/(2). The calculated charge distributions show strong metal-ligand covalency. In fact, as the formal oxidation states of the Mn sites increase, the net Mn charges generally show a slow decrease, consistent with a very strong ligand --> metal charge transfer, particularly from &mgr;-oxo or &mgr;-peroxo ligands. TACN is a better donor ligand than carboxylate, even when calculated on a per donor atom basis. The ligand atom charge transfer order is peroxo >/= oxo >> TACN > acetate. The TACN > acetate ordering is expected from the spectrochemical series, but the strong charge transfer and strong metal-ligand covalency of peroxo and oxo ligands with the Mn sites cannot be simply related to their positions in the spectrochemical series. In the Mn(IV)(2)(&mgr;-O)(2)(&mgr;-O(2))(TACN)(2), each peroxo oxygen has a small charge (-0.3), much less than found for each &mgr;-O atom (-0.7). The high-spin S = 3 state lies quite low in energy, 8 kcal/mol from our calculations and about 4 kcal/mol based on the experimental Heisenberg spin coupling parameters. Potential molecular oxygen dissociation pathways involving a spin S = 1 state are discussed. Effective ligand field diagrams are constructed from the calculated energy levels which display the competition between spin polarization splitting and the ligand field t(2g)-e(g) splitting and allow comparisons of electronic structure among different complexes. The electronic structure and spin couplin...

A large reversible negative magnetic-entropy change ⌬S M has been observed in TbCoC 2 , accompanied by a second-order phase transition at 28 K. The maximum value of −⌬S M is 15.3 J kg −1 K −1 at 30 K for a magnetic-field change from 0 to 5 T, with the refrigerant capacity of 354 J kg −1. In particular, also the large −⌬S M max of 7.8 J kg −1 K −1 , is obtained for a small field change from 0 to 2 T. The large reversible ⌬S M and the high reversible refrigerant capacity in low magnetic field indicate that TbCoC 2 may be a promising candidate for magnetic refrigeration at low temperatures.

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Based on the great advantages of an inner hollow structure and excellent solid counterpart capacity, complex hierarchical structures have been widely used as electrodes for lithium‐ion batteries. Herein, hierarchical yolk–shell Cu2O@CuO‐decorated RGO (YSRs) was designed and synthesized via a multi‐step approach. Octahedron‐like Cu2O‐decorated RGO was firstly produced, in which GO was reduced slightly while cuprous oxide was synthesized. Subsequently, the controlled oxidation of Cu2O@RGO led to the synthesis of special YSRs, which were composed of a solid Cu2O core, spur‐CuO, CuO shell, and RGO covered. As anode materials, YSRs could provide considerable capacity density. Meanwhile, the void existed between shells and solid active materials retaining the advantages of inner hollow structure. As a result, the unique architecture of the materials renders the composites with enhanced electronic and ionic diffusion kinetics, high specific capacity (~894 mAh g‐1, 0.1C), and an excellent rate capability.

Exchange coupling has been realized in textured Nd2Fe14B/α-Fe multilayer films. A Mo spacer layer has proved to be effective for preventing interdiffusion at the interface region between the hard-magnetic Nd16Fe71B13 and the soft-magnetic α-Fe layer in these multilayer films. Anisotropic behavior of the exchange coupling in the films is observed by means of magnetic measurements. Furthermore, the effective critical correlation length is found to exhibit anisotropic behavior, which is smaller in the parallel than in the perpendicular direction at the same temperature. This anisotropic behavior of the multilayer films can be well explained by taking into account the shape anisotropy of the textured grains.

Dy 1−x Pr x ͑Fe 0.35 Co 0.55 B 0.1 ͒ 2 ͑0 ഛ x ഛ 1͒ Laves compounds with a cubic MgCu 2 -type structure were synthesized by arc melting and subsequent annealing. The lattice parameter of the Laves compounds linearly increases, while the Curie temperature T C decreases with increasing Pr content. The saturation magnetization M s at 5 K or 295 K for the Dy 1−x Pr x ͑Fe 0.35 Co 0.55 B 0.1 ͒ 2 alloys decreases to reach a minimum, then increases with increasing Pr content. The composition for magnetic moment compensation is about x = 0.55 at 295 K and x = 0.65 at 5 K, respectively. The magnetostriction ʈ or Ќ at room temperature was investigated either parallel or perpendicular to the applied field using a standard strain gauge technique.

Exchange bias (EB) and magnetic properties of ferrimagnetic (FI) Fe3O4 and antiferromagnetic (AFM) Cr2O3 nanocomposites prepared by mechanical alloying have been investigated. A large EB field of 2.2 kOe at 10 K is observed in one of the nanocomposites, which may be related to the uncompensated and pinned AFM spins at the interface between FI and AFM phases of the nanocomposites. The EB field varies with the strength of cooling field and the content of the Cr2O3 phase, the phenomena observed are explained in terms of interfacial exchange interaction between the two phases.