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Organic-molecular magnets based on a metal-organic framework with chemically tuned electronic and magnetic properties have been attracting tremendous attention due to their promising applications in molecular magnetic sensors, magnetic particle medicines, molecular spintronics, etc. Here, we investigated the magnetic behavior of a heterojunction comprising a ferromagnetic nickel (Ni) film and an organic semiconductor (OSC) 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) layer. Through the magneto-optical Kerr effect (MOKE), a photoemission electron microscopy (PEEM), X-ray magnetic circular dichroism (XMCD), and X-ray photoelectron spectroscopy (XPS), we found that the adsorption of F4-TCNQ on Cu(100)/Ni not only reverses the in-plane magnetization direction originally exhibited by the Ni layer but also results in enhanced magnetic ordering. Furthermore, the cyano group (CN) in adsorbed F4-TCNQ was found spin-polarized along with conspicuous charge transfer with Ni. The density functional theory (DFT) calculations suggest that the experimentally found spin polarization originates from hybridization between the CN group's π orbitals and Ni's d band. These findings signify that the hybrid states at the organic-ferromagnet interface play a key role in tailoring the magnetic behavior of interfaces. For the case of the F4-TCNQ and Ni heterojunction reported here, interface coupling is an antiferromagnetic one.

Substitution of Sn4+ in α-MnO2 improves its structural stability and reveals the influence of disorder on its spin-glass behavior.

The layered manganese oxide cathode materials suffer from the Jahn-Teller effect of the octahedral Mn3+ ions at low potentials and the anionic oxidation triggered structural degradation at high potentials. Introduction of vacancies in the transition metal layer has proved effective in stabilizing the structure at both the high and low potentials. Herein we specially designed vacancy-containing P2-Na2/3[Zn1/9Mn7/9□1/9]O2 (NZMO-Vac) and vacancy-free P2-Na2/3[Zn2/9Mn7/9]O2 (NZMO) to clarify how the vacancies tailor the spinning states of the Mn3+ ions and benefit the structural stability and kinetic performances. The temperature-dependent magnetic susceptibility demonstrates the increase of the Jahn-Teller inactive low-spin Mn3+ ions in NZMO-Vac at low potentials. Density functional theory calculations and advanced physical characterizations further indicate that the TM vacancies facilitate the generation of the low-spin Mn3+ ions by decreasing the Mn-O bond length during discharging. These findings provide new ideas on designing cathode materials with higher specific capacities and robust structures.

Our strategy of polymerizing lithium salt as a polymer electrolyte (3D-SIPE-LiFPA) simultaneously enhances the cycle life and safety characteristics of ultrahigh-energy-density lithium metal batteries (437 W h kg−1).

Electronic structure modulation among multiple metal sites is key to the design of efficient catalysts. Most studies have focused on regulating 3d transition-metal active ions through other d-block metals, while few have utilized f-block metals. Herein, we report a new class of catalyst, namely, UCoO4 with alternative CoO6 and 5f-related UO6 octahedra, as a unique example of a 5f-covalent compound that exhibits enhanced electrocatalytic oxygen evolution reaction (OER) activity because of the presence of the U 5f–O 2p–Co 3d network. UCoO4 exhibits a low overpotential of 250 mV at 10 mA cm–2, surpassing other unitary cobalt-based catalysts ever reported. X-ray absorption spectroscopy revealed that the Co2+ ion in pristine UCoO4 was converted to high-valence Co3+/4+, while U6+ remained unchanged during the OER, indicating that only Co was the active site. Density functional theory calculations demonstrated that the OER activity of Co3+/4+ was synergistically enhanced by the covalent bonding of U6+-5f in the U 5f–O 2p–Co 3d network. This study opens new avenues for the realization of electronic structure manipulation via unique 5f involvement.

The exploitation of high energy and high power densities cathode materials for sodium ion batteries is a challenge. Na-super-ionic-conductor (NASICON) Na4MnV(PO4)3 is one of promising high-performance and low-cost cathode materials, however, still suffers from not reaching the theoretical capacity, low rate capability, and poor cycling stability. In this work, we deploy a novel sodium-deficient NASICON fluorinated phosphate cathode material for sodium ion batteries which demonstrates, notably, high energy and high power densities concomitant with high sodium diffusion kinetics. The enhanced performance of this novel Na3.85⬜0.15MnV(PO3.95F0.05)3 cathode was evidenced by demonstrating a relatively high energy density of ∼380 Wh kg−1 at low rate with much improved rate capability compared to non-doped Na4MnV(PO4)3, and long cycling life over 2000 cycles at high current rates. The structural investigation during battery operation using in situ x-ray diffraction (XRD) reveals bi-phase mechanism with high structural reversibility. The combined XRD and 23Na nuclear magnetic resonance (NMR) analyses demonstrate that the sodium extraction/insertion from Na2 is faster than Na1 site. These findings open promising prospects for unlocking of high energy and high power densities of NASICON phosphate materials by fluorine substitution towards high-performance sodium ion batteries.

International audience; Fe4Nb2O9 and Co4Nb2O9 are antiferromagnetic compounds belonging to the M4M′2O9 series (M = Mn, Fe, Co; M′ = Nb, Ta), whose structure (P[3 with combining macron]c1) derives from the Cr2O3 corundum one. By mixing cobalt and iron in a 1 : 1 ratio, an Fe2Co2Nb2O9 oxide has been synthesized. Its structural, magnetic and electric characterization studies confirm that its unit cell volume (V = 331.19(1) Å3), Néel temperature (TN = 58 K) and dielectric permittivity are intermediate between those of the Fe4Nb2O9 and Co4Nb2O9 end members. The neutron diffraction study evidences an Fe:Co random occupation of the (4d) Wyckoff sites. Its antiferromagnetic structure, refined in the C2/c′ magnetic space group, shows magnetic moments in the planes of the honeycomb (HC) layers of the M4M′2O9 structure, and stacked along c, as for Fe4Nb2O9 and Co4Nb2O9. However, the magnetic field induced magnetization M(H) of Fe2Co2Nb2O9 below TN differs strongly from both end members, exhibiting a sublinear dependence. A similar rounded shape of the electric polarization P(H) curve is evidenced, in marked contrast to the linear M(H) and P(H) behaviours observed below the spin-flop magnetic field for this class of linear magnetoelectric materials. As a result, Fe2Co2Nb2O9 exhibits larger P values and steeper P responses to H at low H than both Fe4Nb2O9 and Co4Nb2O9 end members. This result is explained by a microscopic model based on the Fe and Co mixed occupation. Substitutional disorder locally allows for stronger magnetoelectric couplings and its effect does not cancel on average. This chemical substitution effect opens a new route to enhance the magnetoelectric response of honeycomb antiferromagnets.

Transition metal oxides (TMOs) as high-capacity electrodes have several drawbacks owing to their inherent poor electronic conductivity and structural instability during the multi-electron conversion reaction process. In this study, the authors use an intrinsic high-valent cation substitution approach to stabilize cation-deficient magnetite (Fe

Tailoring the organic–inorganic heterostructure through nanotechnology and molecular engineering is a promising route to achieve high performances of spintronics. Tris(8-hydroxyquinoline)aluminum (...

B-site Os-doped quadruple perovskite oxides LaCu3Fe4-xOsxO12 (x = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCu3Fe4O12 experiences Cu-Fe intermetallic charge transfer that changes the Cu3+/Fe3+ charge combination to Cu2+/Fe3.75+ at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os6+ and mixed Os4.5+ valence states are determined by X-ray absorption spectroscopy for x = 1 and x = 2 compositions, respectively. The x = 1 sample crystallizes in an Fe/Os disordered structure with the Im3 space group. It experiences a spin-glass transition around 480 K. With further Os substitution up to x = 2, the crystal symmetry changes to Pn3, where Fe and Os are orderly distributed in a rocksalt-type fashion at the B site. Moreover, this composition shows a long-range Cu2+(↑)Fe3+(↑)Os4.5+(↓) ferrimagnetic ordering near 520 K. This work provides a rare example for 5d substitution-suppressed intermetallic charge transfer as well as induced structural and magnetic phase transitions with high spin ordering temperature.

The simple ABO3 and A-site-ordered AA′3B4O12 perovskites represent two types of classical perovskite functional materials. There are well-known simple perovskites with ferroelectric properties, while there is still no report of ferroelectricity due to symmetry breaking transition in A-site-ordered quadruple perovskites. Here we report the high pressure synthesis of an A-site-ordered perovskite PbHg3Ti4O12, the only known quadruple perovskite that transforms from high-temperature centrosymmetric paraelectric phase to low-temperature non-centrosymmetric ferroelectric phase. The coordination chemistry of Hg2+ is changed from square planar as in typical A-site-ordered quadruple perovskite to a rare stereo type with 8 ligands in PbHg3Ti4O12. Thus PbHg3Ti4O12 appears to be a combinatory link from simple ABO3 perovskites to A-site-ordered AA′3Ti4O12 perovskites, sharing both displacive ferroelectricity with former and structure coordination with latter. This is the only example so far showing ferroelectricity due to symmetry breaking phase transition in AA′3B4O12-type A-site-ordered perovskites, and opens a direction to search for ferroelectric materials.

Because of the possible crossover of Pb and 3d transition-metal (TM) redox levels, a charge transfer between Pb and TM leads to a continuous evolution from Pb2+Ti4+O3 to Pb4+Ni2+O3 in the perovskit...

The state-of-the-art active HER catalysts in acid media (e.g., Pt) generally lose considerable catalytic performance in alkaline media mainly due to the additional water dissociation step. To address this issue, synergistic hybrid catalysts are always designed by coupling them with metal (hydro)oxides. However, such hybrid systems usually suffer from long reaction path, high cost and complex preparation methods. Here, we discover a single-phase HER catalyst, SrTi0.7Ru0.3O3-δ (STRO) perovskite oxide highlighted with an unusual super-exchange effect, which exhibits excellent HER performance in alkaline media via atomic-scale synergistic active centers. With insights from first-principles calculations, the intrinsically synergistic interplays between multiple active centers in STRO are uncovered to accurately catalyze different elementary steps of alkaline HER; namely, the Ti sites facilitates nearly-barrierless water dissociation, Ru sites function favorably for OH* desorption, and non-metal oxygen sites (i.e., oxygen vacancies/lattice oxygen) promotes optimal H* adsorption and H2 desorption., Efficient electrocatalysts are crucial for the sustainable hydrogen production as an alternative clean fuel. Here, the authors explore a single-phase perovskite oxide as a high-performance hydrogen evolution electrocatalyst via super-exchange induced atomic scale synergistic active sites.

Antiferromagnetic spintronics is an emerging field of non-volatile data storage and information processing. The zero net magnetization and zero stray fields of antiferromagnetic materials eliminate interference between neighbor units, leading to high-density memory integrations. However, this invisible magnetic character at the same time also poses a great challenge in controlling and detecting magnetic states in antiferromagnets. Here, two antiferromagnetic spin states close in energy in strained BiFeO

Epitaxial CoFe2O4(CFO)/CoO bilayers were fabricated by pulsed laser deposition on flexible muscovite mica substrate. Samples with different CFO thicknesses were employed to study the phenomenon of ...

A new oxide, LaMn3Co2Mn2O12, was synthesized under high-pressure (7 GPa) and high-temperature (1423 K) conditions. The compound crystallizes in an AA′3B4O12-type quadruple perovskite structure with...

P2-type Na2/3Ni1/3Mn2/3O2 (P2-NaNM) is a promising cathode material for practical applications in Na-ion batteries due to its high capacity. However, the rearrangement of Na+/vacancy order and cathodic charge order across the Na extraction/intercalation and structural rearrangements of P2-NaNM at high voltages result in rapid capacity fading and insufficient rate capability. Here, a combined structural modulation strategy was presented to solve these challenges via reducing the Na layers spacing through substituting Na sites by Mg ions while simultaneously stabilizing the transition metal (TM) layers through Mg/Ti co-doping. Benefited from the symbiotic effect, P2-NaNM exhibits a significantly enhanced cycling stability and rate capability in the voltage range of 3.0–4.4 ​V. We further revealed that Mn remains Mn4+ while Ni2+ becomes Ni3+ at the surface of Mg/Ti co-substituted P2-NaNM upon charge/discharge process.

In La-Cr-As system, the first ternary compound La3CrAs5 has been successfully synthesized under high- pressure and high-temperature conditions. La3CrAs5 crystallizes into a hexagonal Hf5Sn3Cu-anti type structure with a space group of P 63/ mcm (No. 193) and lattice parameters of a = b = 8.9845 A and c = 5.8897 A. The structure contains face-sharing octahedral CrAs6 chains along the c -axis, which are arranged triangularly in the ab -plane and separated by a significantly large distance of 8.9845 A. The magnetic properties, resistivity and specific heat measurements were performed. La3CrAs5 exhibits a metallic state with Fermi liquid behavior at low temperatures and undergoes a ferromagnetic transition at Curie temperature T C ~50 K. First-principles theoretical studies were conducted to calculate its band structure and density of states (DOS), which indicated that the non-negligible contribution of La to the DOS near the Fermi level caused La3CrAs5 to be a three-dimensional (3D) metal. The crystal orbital Hamilton population (−COHP) was also calculated to explain the global stability and bonding characteristics in the structure of La3CrAs5.

Perovskite-based oxides have emerged as promising oxygen evolution reaction (OER) electrocatalysts. The performance is closely related to the lattice, electronic, and defect structure of the oxides, which determine surface and bulk properties and consequent catalytic activity and durability. Further, interfacial interactions between phases in a nanocomposite may affect bulk transportation and surface adsorption properties in a similar manner to phase doping except without solubility limits. Herein, we report the development of a single/double perovskite nanohybrid with limited surface self-reconstruction capability as an OER electrocatalyst. Such superior performance arises from a structure that maintains high crystallinity post OER catalysis, in addition to forming an amorphous layer following the self-reconstruction of a single perovskite structure during the OER process. In situ X-ray absorption near edge structure spectroscopy and high-resolution synchrotron-based X-ray diffraction reveal an amorphization process in the hybrid single/double perovskite oxide system that is limited in comparison to single perovskite amorphization, ensuring high catalytic activity.