Understanding of magnetic behavior of the pseudo-binary Co2-xNixZn11: in the light of crystal and electronic structures.

A high-temperature synthetic approach is used to prepare a series of pseudo-binary phases-Co2-xNixZn11. In the structures of Co2-xNixZn11, the statistical distribution between Co and Ni that is suggested by compositional analysis is confirmed by combined refinements of X-ray and neutron powder diffraction (NPD) experimental data. The aforementioned phases adopt a body-centered cubic lattice with a noncentrosymmetric space group I4̄3m (217). Their crystal structures comprise two 26-atom γ-brass clusters. Each γ-cluster is made of four sequential polyhedral shells: inner tetrahedron (IT), outer tetrahedron (OT), octahedron (OH), and distorted cuboctahedron (CO). Diffraction experiments and the computations endorse that the OT site is statistically distributed by Co and Ni atoms, while the other three sites (IT, OH, and CO) are occupied by Zn atoms. The density of states (DOS) curve for Co1.5Ni0.5Zn11 displays a similar feature as binary Co2Zn11, whereas the wide pseudo-gap is formed near EF as Ni-concentration increases in Co2-xNixZn11. Bonding analysis shows that this specific atomic distribution nearly optimizes heteroatomic Co/Ni-Zn contacts in the Co1.0Ni1.0Zn11 and Co0.5Ni1.5Zn11. The Co1.7Ni0.3Zn11 exhibit paramagnetic behavior, whereas Co0.5Ni1.5Zn11 shows distinct diamagnetic behavior. With the increase in Ni concentration in the structure of Co2-xNixZn11, Ni atoms gradually substitute the Co atoms at OT sites; hence, magnetic characteristics change from para- to diamagnetism.

Colossal Zero-Field-Cooled Exchange Bias via Tuning Compensated Ferrimagnetic in Kagome Metals.

Exchange bias (EB) is a crucial property with widespread applications but particularly occurs by complex interfacial magnetic interactions after field cooling. To date, intrinsic zero-field-cooled EB (ZEB) has only emerged in a few bulk frustrated systems and their magnitudes remain small yet. Here, enabled by high temperature synthesis, we uncover a colossal ZEB field of 4.95 kOe via tuning compensated ferrimagnetism in a family of kagome metals, which is almost twice the magnitude of known materials. Atomic-scale structure, spin dynamics, and magnetic theory revealed that these compensated ferrimagnets originate from significant antiferromagnetic exchange interactions embedded in the holmium-iron ferrimagnetic matrix due to supersaturated preferential manganese doping. A random antiferromagnetic order of manganese sublattice sandwiched between ferromagnetic iron kagome bilayers accounts for such unconventional pinning. The outcome of the present study outlines disorder-induced giant bulk ZEB and coercivity in layered frustrated systems.

Enhancing P2/O3 Biphasic Cathode Performance for Sodium-Ion Batteries: A Metaheuristic Approach to Multi-Element Doping Design.

Sodium-ion batteries (SIBs) have emerged as a compelling alternative to lithium-ion batteries (LIBs), exhibiting comparable electrochemical performance while capitalizing on the abundant availability of sodium resources. In SIBs, P2/O3 biphasic cathodes, despite their high energy, require furthur improvements in stability to meet current energy demands. This study introduces a systematic methodology that leverages the meta-heuristically assisted NSGA-II algorithm to optimize multi-element doping in electrode materials, aiming to transcend conventional trial-and-error methods and enhance cathode capacity by the synergistic integration of P2 and O3 phases. A comprehensive phase analysis of the meta-heuristically designed cathode material Na0.76Ni0.20Mn0.42Fe0.30Mg0.04Ti0.015Zr0.025O2 (D-NFMO) is presented, showcasing its remarkable initial reversible capacity of 175.5 mAh g-1 and exceptional long-term cyclic stability in sodium cells. The investigation of structural composition and the stabilizing mechanisms is performed through the integration of multiple characterization techniques. Remarkably, the irreversible phase transition of P2→OP4 in D-NFMO is observed to be dramatically suppressed, leading to a substantial enhancement in cycling stability. The comparison with the pristine cathode (P-NFMO) offers profound insights into the long-term electrochemical stability of D-NFMO, highlighting its potential as a high-voltage cathode material utilizing abundant earth elements in SIBs. This study opens up new possibilities for future advancements in sodium-ion battery technology.

Seeing the Unseen: The Structural Influence of the Lone Pair Electrons in PbWO4.

Pair distribution function (PDF) analysis of the scheelite-type material PbWO4 reveals previously unidentified short-range structural distortions in the PbO8 polyhedra and WO4 tetrahedra not observed in the similarly structured CaWO4. These local distortions are a result of the structural influence of the Pb2+ 6s2 lone pair electrons. These are not evident from the Rietveld analysis of synchrotron X-ray or neutron powder diffraction data, nor do they strongly influence the X-ray PDF (XPDF). This illustrates the importance of neutron PDF (NPDF) in the study of such materials. First-principles density function theory (DFT) calculations show that the Pb2+ 6s2 electrons are hybridized with the O2- 2p electrons near the Fermi level. The presence of local-scale distortions has previously been neglected in studies of structure-functionality relationships in PbWO4 and other scheelite-structured photocatalytic materials, including BiVO4, and this observation opens new avenues for their optimization.

Mechanochemically Enabled Metastable Niobium Tungsten Oxides.

Metastable compounds have greatly expanded the synthesizable compositions of solid-state materials and have attracted enormous amounts of attention in recent years. Especially, mechanochemically enabled metastable materials synthesis has been very successful in realizing cation-disordered materials with highly simple crystal structures, such as rock salts. Application of the same strategy for other structural types, especially for non-close-packed structures, is peculiarly underexplored. Niobium tungsten oxides (NbWOs), a class of materials that have been under the spotlight because of their diverse structural varieties and promising electrochemical and thermoelectric properties, are ideally suited to fill such a knowledge gap. In this work, we develop a new series of metastable NbWOs and realize one with a fully cation-disordered structure. Furthermore, we find that metastable NbWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close-packed-close-packed conversion process, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. Finally, by comparing the cation-disordered NbWO with other trending cation-disordered oxides, we raise a few key structural features for cation disorder and suggest a few possible research opportunities for this field.

Nitrogen-Rich Molybdenum Nitride Synthesized in a Crucible under Air.

The triple bond in N2 is significantly stronger than the double bond in O2, meaning that synthesizing nitrogen-rich nitrides typically requires activated nitrogen precursors, such as ammonia, plasma-cracked atomic nitrogen, or high-pressure N2. Here, we report a synthesis of nitrogen-rich nitrides under ambient pressure and atmosphere. Using Na2MoO4 and dicyandiamide precursors, we synthesized nitrogen-rich γ-Mo2N3 in an alumina crucible under an ambient atmosphere, heated in a box furnace between 500 and 600 °C. Byproducts of this metathesis reaction include volatile gases and solid Na(OCN), which can be washed away with water. X-ray diffraction and neutron diffraction showed Mo2N3 with a rock salt structure having cation vacancies, with no oxygen incorporation, in contrast to the more common nitrogen-poor rock salt Mo2N with anion vacancies. Moreover, an increase in temperature to 700 °C resulted in molybdenum oxynitride, Mo0.84N0.72O0.27. This work illustrates the potential for dicyandiamide as an ambient-temperature metathesis precursor for an increased effective nitrogen chemical potential under ambient conditions. The classical experimental setting often used for solid-state oxide synthesis, therefore, has the potential to expand the nitride chemistry.

Na2.5Cr0.5Zr0.5Cl6: A New Halide-Based Fast Sodium-Ion Conductor.

All-solid-state batteries employing solid electrolytes (SEs) have received widespread attention due to their high safety. Recently, lithium halides are intensively investigated as promising SEs while their sodium counterparts are less studied. Herein, a new sodium-ion conductor with a chemical formula of Na2.5Cr0.5Zr0.5Cl6 is reported, which exhibits high room temperature ionic conductivity of 0.1 mS cm-1 with low migration energy barrier of ≈0.41 eV. Na2.5Cr0.5Zr0.5Cl6 has a Fm-3m structure with 41.67 mol.% of cationic vacancies owing to the occupation of Cr (8.33 mol.%) and Zr (8.33 mol.%) ions at Na sites. Supercell calculations show that the lowest columbic energy configuration has Cr/Zr/V (where V is the vacancy) clusters in the structure. Nonetheless, the clusters have mixed effects on the sodium ion conduction pathway, based on the Bond Valence Energy Landscape calculation. A global 3D Na-ion transport percolation network can be revealed in the lowest energy supercell. Effective pathways are connected through the NaCl6 and VCl6 nodes. Besides, Raman spectroscopy and 23Na solid-state nuclear magnetic resonance spectroscopy further prove the tunable structure of the SEs with different Cr to Zr ratios. The optimization between the concentration of Na+ and vacancies is crucial to create an improved network of Na+ diffusion channels.

Promoting high-voltage stability through local lattice distortion of halide solid electrolytes.

Stable solid electrolytes are essential to high-safety and high-energy-density lithium batteries, especially for applications with high-voltage cathodes. In such conditions, solid electrolytes may experience severe oxidation, decomposition, and deactivation during charging at high voltages, leading to inadequate cycling performance and even cell failure. Here, we address the high-voltage limitation of halide solid electrolytes by introducing local lattice distortion to confine the distribution of Cl-, which effectively curbs kinetics of their oxidation. The confinement is realized by substituting In with multiple elements in Li3InCl6 to give a high-entropy Li2.75Y0.16Er0.16Yb0.16In0.25Zr0.25Cl6. Meanwhile, the lattice distortion promotes longer Li-Cl bonds, facilitating favorable activation of Li+. Our results show that this high-entropy halide electrolyte boosts the cycle stability of all-solid-state battery by 250% improvement over 500 cycles. In particular, the cell provides a higher discharge capacity of 185 mAh g-1 by increasing the charge cut-off voltage to 4.6 V at a small current rate of 0.2 C, which is more challenging to electrolytes|cathode stability. These findings deepen our understanding of high-entropy materials, advancing their use in energy-related applications.

Controlling the Superconductivity of Nb2PdxS5 via Reversible Li Intercalation.

The Nb2PdxS5 (x ≈ 0.74) superconductor with a Tc of 6.5 K is reduced by the intercalation of lithium in ammonia solution or electrochemically to produce an intercalated phase with expanded lattice parameters. The structure expands by 2% in volume and maintains the C2/m symmetry and rigidity due to the PdS4 units linking the layers. Experimental and computational analysis of the chemically synthesized bulk sample shows that Li occupies triangular prismatic sites between the layers with an occupancy of 0.33(4). This level of intercalation suppresses the superconductivity, with the injection of electrons into the metallic system observed to also reduce the Pauli paramagnetism by ∼40% as the bands are filled to a Fermi level with a lower density of states than in the host material. Deintercalation using iodine partially restores the superconductivity, albeit at a lower Tc of ∼5.5 K and with a smaller volume fraction than in fresh Nb2PdxS5. Electrochemical intercalation reproduces the chemical intercalation product at low Li content (<0.4) and also enables greater reduction, but at higher Li contents (≥0.4) accessed by this route, phase separation occurs with the indication that Li occupies another site.

Tetrahedral triple-Q magnetic ordering and large spontaneous Hall conductivity in the metallic triangular antiferromagnet Co1/3TaS2.

The triangular lattice antiferromagnet (TLAF) has been the standard paradigm of frustrated magnetism for several decades. The most common magnetic ordering in insulating TLAFs is the 120° structure. However, a new triple-Q chiral ordering can emerge in metallic TLAFs, representing the short wavelength limit of magnetic skyrmion crystals. We report the metallic TLAF Co1/3TaS2 as the first example of tetrahedral triple-Q magnetic ordering with the associated topological Hall effect (non-zero σxy(H = 0)). We also present a theoretical framework that describes the emergence of this magnetic ground state, which is further supported by the electronic structure measured by angle-resolved photoemission spectroscopy. Additionally, our measurements of the inelastic neutron scattering cross section are consistent with the calculated dynamical structure factor of the tetrahedral triple-Q state.