Tunable Anomalous Hall Effect in a Kagomé Ferromagnetic Weyl Semimetal.

Emerging from the intricate interplay of topology and magnetism, the giant anomalous Hall effect (AHE) is the most known topological property of the recently discovered kagomé ferromagnetic Weyl semimetal CoSnS with the magnetic Co atoms arranged on a kagomé lattice. Here it is reported that the AHE in CoSnS can be fine-tuned by an applied magnetic field orientated within ≈2° of the kagomé plane, while beyond this regime, it stays unchanged. Particularly, it can vanish in magnetic fields parallel to the kagomé plane and even decrease in magnetic fields collinear with the spin direction.

Twisting two-dimensional iron sulfide layers into coincident site superlattices intercalation chemistry.

Layered van der Waals (vdW) materials are susceptible not only to various stacking polymorphs through translations but also twisted structures due to rotations between layers. Here, we study the influence of such layer-to-layer twisting through the intercalation of ethylenediamine (EDA) molecules into tetragonal iron sulfide (Mackinawite FeS). Selected area electron diffraction patterns of intercalated FeS display reflections corresponding to multiple square lattices with a fixed angle between them, contrary to a single square lattice seen in the unintercalated phase.

Metal Sulfide Ion Exchangers: High Acid Stability of NaMgSnS (NMS) and Topotactic Conversion to 2D Solid Acids with Semiconducting Character.

Metal sulfide ion exchange materials (MSIEs) are of interest for nuclear waste remediation applications. We report the high stability of two structurally related metal sulfide ion exchange materials, NaMgSnS (Mg-NMS) and NaSnS (Na-NMS), in strongly acid media, in addition to the preparation of NaNiSnS (Ni-NMS). Their formation progress during synthesis is studied with in-situ methods, with the target phases appearing in <15 min, reaction completion in <12 h, and high yields (75-80%).

Kanatzidisite: A Natural Compound with Distinctive van der Waals Heterolayered Architecture.

New minerals have long been a source of inspiration for the design and discovery. Many quantum materials, including superconductors, quantum spin liquids, and topological materials, have been unveiled through mineral samples with unusual structure types. In this report, we present kanatzidisite, a new naturally occurring material with formula [BiSbS][Te] and monoclinic symmetry (space group of 2/) with lattice parameters = 4.

Sr(Ag Li ) Se and [Sr Se ][(Ag Li ) Se ] Tunable Direct Band Gap Semiconductors.

Synthesizing solids in molten fluxes enables the rapid diffusion of soluble species at temperatures lower than in solid-state reactions, leading to crystal formation of kinetically stable compounds. In this study, we demonstrate the effectiveness of mixed hydroxide and halide fluxes in synthesizing complex Sr/Ag/Se in mixed LiOH/LiCl. We have accessed a series of two-dimensional Sr(Ag Li ) Se layered phases.

Discovery of chalcogenides structures and compositions using mixed fluxes.

Advancements in many modern technologies rely on the continuous need for materials discovery. However, the design of synthesis routes leading to new and targeted solid-state materials requires understanding of reactivity patterns. Advances in synthesis science are necessary to increase efficiency and accelerate materials discovery.

Tuning the Structural and Magnetic Properties in Mixed Cation MnCoPS.

The metal thiophosphates (MTP), PS, are a versatile class of van der Waals materials, which are notable for the possibility of tuning their magnetic properties with the incorporation of different transition-metal cations. Further, they also offer opportunities to probe the independent and synergistic role of the magnetically active cation sublattice when coupled to PQ polyhedra. Herein, we report the structural, magnetic, and electronic properties of the series of MTPs, MnCoPS ( = 0.

Low Thermal Conductivity in Heteroanionic Materials with Layers of Homoleptic Polyhedra.

Although BiAgOSe, an analogue of a well-studied thermoelectric material BiCuOSe, is thermodynamically stable, its synthesis is complicated by the low driving force of formation from the stable binary and ternary intermediates. Here we have developed a "subtraction strategy" to suppress byproducts and produce pure phase BiAgOSe using hydrothermal methods. Electronic structure calculations and optical characterization show that BiAgOSe is an indirect bandgap semiconductor with a bandgap of 0.

New Compounds and Phase Selection of Nickel Sulfides via Oxidation State Control in Molten Hydroxides.

Molten salts are promising reaction media candidates for the discovery of novel materials; however, they offer little control over oxidation state compared to aqueous solutions. Here, we demonstrated that when two hydroxides are mixed, their melts become fluxes with tunable solubility, which are surprisingly powerful solvents for ternary chalcogenides and offer effective paths for crystal growth to new compounds. We report that precise control of the oxidation state of Ni is achievable in mixed molten LiOH/KOH to grow single crystals of all known ternary K-Ni-S compounds.

A two-dimensional type I superionic conductor.

Superionic conductors possess liquid-like ionic diffusivity in the solid state, finding wide applicability from electrolytes in energy storage to materials for thermoelectric energy conversion. Type I superionic conductors (for example, AgI, AgSe and so on) are defined by a first-order transition to the superionic state and have so far been found exclusively in three-dimensional crystal structures. Here, we reveal a two-dimensional type I superionic conductor, α-KAgSe, by scattering techniques and complementary simulations.

On the Electrochemical Phase Evolution of Anti-PbO-Type CoSe in Alkali Ion Batteries.

The reaction mechanism of anti-PbO type CoSe in Li, Na, and K ion half cells is studied. Ex situ X-ray diffraction data is analyzed with the Rietveld method, in conjunction with discharge profiles and extended cycling data. These indicate that intercalation followed by a conversion reaction occur in all systems.

Contrasting SnTe-NaSbTe and SnTe-NaBiTe Thermoelectric Alloys: High Performance Facilitated by Increased Cation Vacancies and Lattice Softening.

Defect chemistry is critical to designing high performance thermoelectric materials. In SnTe, the naturally large density of cation vacancies results in excessive hole doping and frustrates the ability to control the thermoelectric properties. Yet, recent work also associates the vacancies with suppressed sound velocities and low lattice thermal conductivity, underscoring the need to understand the interplay between alloying, vacancies, and the transport properties of SnTe.

Structure and Interface Design Enable Stable Li-Rich Cathode.

Li-rich layered-oxide cathodes have the highest theoretical energy density among all the intercalated cathodes, which have attracted intense interests for high-energy Li-ion batteries. However, O3-structured layered-oxide cathodes suffer from a low initial Coulombic efficiency (CE), severe voltage fade, and poor cycling stability because of the continuous oxygen release, structural rearrangements due to irreversible transition-metal migration, and serious side reactions between the delithiated cathode and electrolyte. Herein, we report that these challenges are migrated by using a stable O2-structured LiNiCoMnO (O2-LR-NCM) and all-fluorinated electrolyte.

Long-range magnetic order in hydroxide-layer-doped (Li Fe Mn OD)FeSe.

The (Li Fe OH)FeSe superconductor has been suspected of exhibiting long-range magnetic ordering due to Fe substitution in the LiOH layer. However, no direct observation such as magnetic reflection from neutron diffraction has been reported. Here, we use a chemical design strategy to manipulate the doping level of transition metals in the LiOH layer to tune the magnetic properties of the (Li Fe Mn OD)FeSe system.

Proton and ammonia intercalation into layered iron chalcogenides.

Structurally related to the iron-based superconductors, two new intercalated iron chalcogenides (H0.5NH3)Fe2Ch2 where Ch = S, Se have been prepared. By topochemical conversion, the protons were exchanged by lithium to form (Li0.

High-Performance All-Solid-State Na-S Battery Enabled by Casting-Annealing Technology.

Room-temperature all-solid-state Na-S batteries (ASNSBs) using sulfide solid electrolytes are a promising next-generation battery technology due to the high energy, enhanced safety, and earth abundant resources of both sodium and sulfur. Currently, the sulfide electrolyte ASNSBs are fabricated by a simple cold-pressing process leaving with high residential stress. Even worse, the large volume change of S/NaS during charge/discharge cycles induces additional stress, seriously weakening the less-contacted interfaces among the solid electrolyte, active materials, and the electron conductive agent that are formed in the cold-pressing process.

Self-Templated Formation of P2-type KCoO Microspheres for High Reversible Potassium-Ion Batteries.

Layered metal oxides have been widely used as the best cathode materials for commercial lithium-ion batteries and are being intensively explored for sodium-ion batteries. However, their application to potassium-ion batteries (PIBs) is hampered because of the poor cycling stability and low rate capability due to the larger ionic size of K than of Li or Na. Herein, a facile self-templated strategy was used to synthesize unique P2-type KCoO microspheres that consist of aggregated primary nanoplates as PIB cathodes.

Superconductivity and magnetism in iron sulfides intercalated by metal hydroxides.

Inspired by naturally occurring sulfide minerals, we present a new family of iron-based superconductors. A metastable form of FeS known as the mineral mackinawite forms two-dimensional sheets that can be readily intercalated by various cationic guest species. Under hydrothermal conditions using alkali metal hydroxides, we prepare three different cation and metal hydroxide-intercalated FeS phases including (Li Fe OH)FeS, [(Na Fe )(OH)]FeS, and K Fe S.

Metastable Layered Cobalt Chalcogenides from Topochemical Deintercalation.

We present a general strategy to synthesize metastable layered materials via topochemical deintercalation of thermodynamically stable phases. Through kinetic control of the deintercalation reaction, we have prepared two hypothesized metastable compounds, CoSe and CoS, with the anti-PbO type structure from the starting compounds KCoSe and KCoS, respectively. Thermal stability, crystal structure from X-ray and neutron diffraction, magnetic susceptibility, magnetization, and electrical resistivity are studied for these new layered chalcogenides; both CoSe and CoS are found to be weak itinerant ferromagnets with Curie temperatures close to 10 K.