Inorganic-organic hybrid compound, [Fe(tren)(ea)][Fe2Se3]2 (tren = tris(2-aminoethyl)amine C6H18N4; ea = ethanolamine, C2H7NO) has been synthesized by a solvothermal reaction using stoichiometric tren and excessive ea. The compound comprises mixed-valent [Fe2Se3]1- double chains and trigonal bipyramidal (TBP) [Fe(tren)(ea)]2+ complexes. This is the first report of Fe-Se hybrid materials with interstitial Fe-amine complexes in TBP geometry. Low-field magnetic measurements reveal a bifurcation between the field-cooled and zero-field-cooled magnetization curves at 26 K. Measurements under AC applied field show frequency-dependent peaks in the in-phase part of magnetic susceptibility, indicating the system behaves as cluster spin glass. Nevertheless, under applied field of 2 T, heat capacity measurements show a peak at 24 K, suggesting transition to a long-range magnetically ordered state. The moderately negative Weiss constant, θw = - 52(1) K, is indicative of antiferromagnetic nearest-neighbor interactions within the chains. The isothermal magnetization curve displays a multistep hysteresis loop due to a potential spin-reorientation transition, with a high coercivity of approximately 0.75 T. X-ray absorption spectroscopy confirms the mixed-valent nature of the [Fe2Se3] double chains. The 57Fe Mössbauer spectroscopy reveals complex magnetic ordering in [Fe2Se3] chains at 6 K. Additionally, magnetic splitting of the signal emerging from the [Fe(tren)(ea)]2+ complex is observed, indicating magnetic interactions between complexes and chains. This hypothesis was confirmed by a comparative DFT analysis of the reported compound and a hypothetical [Zn(tren)(ea)][Fe2Se3]2, which features nonmagnetic ions in the complex.

We report the synthesis and magnetic characterization of WFeB and identify it as a metallic d-wave altermagnet representative of a broader TiNiSi-type family. Neutron diffraction, Mössbauer spectroscopy, and magnetometry establish a collinear altermagnetic ordering confirmed by first-principles calculations. The electronic structure shows a nonrelativistic spin splitting of approximately 100 meV, but it also supports a strong spin-splitter transport response. This demonstrates that efficient spin-current generation can occur even with such modest band splitting. Symmetry analysis shows that selected film orientations permit deterministic switching of the Néel vector by current-induced staggered torques, enabling electrical control of a perpendicular spin-splitter response. These results establish WFeB and related TiNiSi-type antiferromagnets as a platform for electrically switchable charge-to-spin conversion driven by altermagnetic symmetry.

Intermetallic compounds and multicomponent refractory alloys exhibit numerous applications in catalysis, magnetism, and energy conversion, yet their synthesis remains challenging due to the refractory nature of their constituent elements and inherently sluggish nature of solid-state diffusion that requires extreme reaction temperatures. Herein, we introduce a general CsCl-mediated molten-salt synthetic method that enables single-step, moderate-temperature (<1050 °C) access to finely dispersed single-phase polycrystalline metallic materials across diverse structural families. Binary alloys with melting temperatures over 2000 °C, Laves-type intermetallics, the incongruently melting complex intermetallics such as μ-phase Fe7Mo6, and multimetallic high-entropy alloys (HEAs) were successfully prepared by this facile method. For Fe7Mo6, the synthesis enabled further characterization of magnetic and electrocatalytic properties. The CsCl flux mediates a dissolution-reprecipitation pathway that yields homogeneous polycrystalline powders with controlled stoichiometry. Such alloys and intermetallics can be further converted to corresponding multimetallic MXides, while preserving metal stoichiometry, as demonstrated for phosphides, carbides, borides, and sulfides. Overall, this work establishes a robust and scalable synthetic platform for the facile synthesis of compositionally and structurally diverse refractory multimetallic systems.

Binary transition metal phosphides and their solid solutions have emerged as promising hydrogen evolution reaction (HER) catalysts. Although many research endeavors have adopted strategies to vary compositions to optimize catalytic performance, they mainly focus on binary structures, which represent only a small fraction of the abundant phase space of structure types among transition metal phosphides. The largely unexplored class of ternary and multinary ordered phosphides in catalysis comprises two or more metals with quite different chemical nature, concealing the structure-property relationships essential for advancing catalyst design. Here, we explored phosphides crystallizing in one of the most abundant ordered intermetallic structure types, -the ThCr2Si2 type, -where square nets of 3d transition metal M and P atoms are separated by layers of electropositive Ba cations. Four ternary BaM2P2 (M = Fe, Fe/Cu, Fe/Ni, Ni) catalysts were synthesized and characterized. BaNi2P2 showed high HER activity in acidic electrolyte, which required an overpotential, eta(10), of only 62 mV to drive current density j = -10 mA/cm(2) and high stability with a potential drop rate of 0.25 mV/h. BaNi2P2 outperformed other Ni-based catalysts, such as Ni2P and Ni5P4. Notably, at current densities above -170 mA/cm(2), BaNi2P2 outperformed the standard Pt electrode measured under identical conditions. Electronic structure analysis revealed a volcano-type activity trend among the four BaM2P2 catalysts based on their d-band center positions, highlighting the role of electropositive Ba cations in shifting the Ni-3d orbitals into an optimal position.

PtSiSb is a compound with covalent Si-Sb bonds, which are relatively rare instances in solid-state materials. The original report on PtSiSb indicates synthetic challenges for the isolation of single-phase samples, as well as potential discrepancies in the predicted electronic structure and experimental transport properties. We considered PtSiSb as a case study with the objective of demonstrating the importance of synthesis as a bridge between theoretical predictions and experimental properties. Using guidance from in situ powder X-ray diffraction, the synthesis of single-phase polycrystalline samples was developed, allowing further experimental characterization of transport and catalytic properties. Thermal conductivity and heat capacity demonstrated anomalous behavior, indicating an unconventional phonon scattering mechanism in PtSiSb. Charge transport measurements indicated semimetallic behavior. Hydrogen evolution reaction (HER) tests in acidic electrolyte revealed that the PtSiSb cathode needs an overpotential η10 = 120 mV to achieve a current density j = -10 mA/cm2. This is lower activity than elemental Pt but comparable to known and active transition-metal phosphide HER catalysts, such as CoP, with η10 = 93 mV when measured at identical conditions.

Metal silicon phosphides composed of earth-abundant Si and P tend to exhibit semiconducting properties and adopt diverse crystal structures with relatively small additions of structure-directing elements. The potential of silicon phosphide materials in nonlinear optical applications has been hindered by the inability to systematically produce noncentrosymmetric structures with such a flexible framework. In this work, two isostructural compounds with a novel noncentrosymmetric structure were made possible by the inclusion of elements with stereochemically active lone pairs (Sn2+ and Pb2+). The structures were determined through single-crystal and synchrotron powder X-ray diffraction. Analysis of chemical bonding in real space through the electron localization function revealed stereochemically active Pb2+ and Sn2+ species in a trigonal pyramidal coordination with {Pb/Sn}-P bonds. Such covalent bonding between Pb and P is quite uncommon in extended solids and has been reported in a few rare instances. Band structure calculations and linear optical measurements confirm the semiconducting nature of CsXSi15P21 (X = Sn or Pb). The synthesis was optimized to yield high-purity polycrystalline samples. The nonlinear optical properties show promising second-harmonic generation (SHG) coefficients from the Kurtz-Perry method. First-principles calculations of the nonlinear optical properties support the experimentally determined SHG values and provide moderate values of birefringence, suggesting CsXSi15P21 could be phase-matchable and practical nonlinear optical materials in the mid-IR region.

Boron-based compounds exhibit a wide range of structural diversity, with potential applications spanning organic and inorganic chemistry. Herein, we focus on the characterization of the linear boron-phosphorus unit PBP in Na3BP2 using solid-state nuclear magnetic resonance (ssNMR) spectroscopy and density functional theory (DFT) calculations. High-resolution 11B ssNMR spectra were recorded at two fields, and key parameters such as chemical shift anisotropy (CSA), quadrupolar coupling constants (CQ), and electric field gradient (EFG) tensors were extracted. The 11B NMR results revealed a distinct chemical environment for the two-coordinate boron atom, with a CSA span (Ω) of 280 ppm and a CQ of 3.0 MHz. These values were further validated through periodic plane-wave DFT calculations, which showed good agreement with experimental results. The obtained spectral parameters are compared to other linear boron units, such as the BO2 motif, providing a broader context for understanding boron coordination in inorganic compounds. This work expands the body of NMR knowledge on boron-containing materials, particularly for linear boron motifs. The findings contribute to the growing field of boron chemistry and its potential applications in advanced materials.

Transition-metal phosphides (MPs) are promising earth-abundant catalysts for hydrogen evolution reactions (HERs) due to their remarkable activity and stability. To further improve their properties, facet control is a key strategy. The growth of shape-selected nanoparticles may substantially enhance electrocatalytic activity, but this approach requires fundamental studies of facet-specific catalytic properties. There are only a few reports on the facet effects of MPs, which leads to a limited understanding of the activity of each facet and hampers catalyst design. Here, we grew large hexagonal-prism-shaped single crystals of three representative M2P (M = Ni, Co, and Fe) catalysts using metal flux routes. Two facets of M2P single crystals were tested to study facet-dependent HER activities, and it was consistently demonstrated that for all M2P crystals, a tip facet [(0001) for Ni2P/Fe2P and (010) for Co2P] had a higher activity than the side facet [(1010) for Ni2P/Fe2P and (100) for Co2P]. HER activity between the same facet elucidated the activity ordered between different transition metals as Fe2P > Co2P > Ni2P under low-potential regions. At high applied potentials, this trend is reversed due to the differences in Tafel slopes, with Ni2P becoming the most active catalyst, such that the activity of the (0001) facet of Ni2P approaches that of Pt. The calculated surface density of states (DOS) of each facet and its local curvature were found to be a useful descriptor for the activity trends among different transition metals of the same facets.

Thin-film photovoltaic technology has advantages to silicon in terms of flexibility, lower manufacturing energy needs, and use in tandem cells. However, the high-efficiency thin-film technologies available (e.g., CIGS, CdTe or halide perovskites) have issues in terms of cost, element abundance, or long-term stability. Finding new solar absorbers is a slow process involving complex experimental synthesis and characterization. Firstprinciples computations on the other hand offer an attractive way to speed up this process. Here, we will report on a large-scale highthroughput computational search for new solar absorbers among known inorganic materials. Importantly, the need for high carrier lifetime is taken into account by including in the screening intrinsic defects and their role as potential Shockley-Read-Hall recombination centers. Screening similar to 40,000 known inorganic compounds, we identify a handful of promising new solar absorbers. I will discuss the chemistries that we identified and highlight a few interesting candidates. I will especially focus on BaCd2P2, a Zintl phosphide where our follow-up experiments confirm the promising properties including a similar to 1.5 eV direct band gap but also bright band-edge photoluminescence, long carrier lifetime, and high stability. Beyond BaCd2P2, our work highlights the discovery of an entire family of AM(2)P(2) Zintl phosphides with our recent exciting results on CaZn2P2 thin films.

While molecular dynamics (MD) is a very useful computational method for atomistic simulations, modeling the interatomic interactions for reliable MD simulations of real materials has been a long-standing challenge. In 2007, Behler and Parrinello first proposed and demonstrated an artificial neural network machine learning (ANN-ML) scheme, opening a new paradigm for developing accurate and efficient interatomic potentials for reliable MD simulation studies of the thermodynamics and kinetics of materials. In this paper, we show that an accurate and transferable ANN-ML interatomic potential can be developed for MD simulations of the La-Si-P system. The crucial role of training data in the ML potential development is discussed. The developed ANN-ML potential accurately describes not only the energy vs volume curves for all the known elemental, binary, and ternary crystalline structures in the La-Si-P system but also the structures of La-Si-P liquids with various compositions. Using the developed ANN-ML potential, the melting temperatures of several crystalline phases in the La-Si-P system are predicted by the coexistence of solid-liquid phases from MD simulations. While the ANN-ML model systematically underestimates the melting temperatures of these phases, the overall trend agrees with experiment. The developed ANN-ML potential is also applied to study the nucleation and growth of LaP as a function of different relative concentrations of Si and P in the La-Si-P liquid, and the obtained results are consistent with experimental observations.

Borides are a rich material family. To push the boundaries of borides' properties and applications into broader fields, we have conducted systematic theoretical and experimental searches for synthesizable phases in ternary borides TM_2B_2 (T = 3d, M = 4d/5d transition metals). We find that TM_2B_2 in the FeMo_2B_2-type and CoW_2B_2-type structures form a large family of stable/metastable materials of 120 members. Among them, we identify 40 materials with stable magnetic solutions. Further, we discover 11 altermagnets in the FeMo_2B_2-type structure. So far, boride altermagnets are rare. In these altermagnets, T = Fe or Mn atoms are arranged in parallel T-chains with strong ferromagnetic intrachain couplings and antiferromagnetic interchain couplings. They simultaneously exhibit electronic band spin splitting, typical of ferromagnetism, and zero net magnetization, typical of antiferromagnetism. They also exhibit magnonic band chiral splitting. Both effects originate from the unique altermagnetic symmetries crucially constrained by the nonmagnetic atoms in the structure. Transport properties of relevance to spintronic applications, including the strain-induced spin-splitter effect and anomalous Hall effect, are predicted. An iodine-assisted synthesis method for TM_2B_2 is developed, using which 7 of the predicted low-energy phases are experimentally synthesized and characterized, including 4 altermagnets. This work expands the realm of borides by offering new opportunities for studying altermagnetism and altermagnons in borides. It also provides valuable insights into the discovery and design of altermagnets. By demonstrating that altermagnets can exist as families sharing a common motif, this work paves a feasible route for discovering altermagnets by elemental substitutions and high-throughput computations.

ThCr2Si2-type layered materials are a large family of compounds with applications ranging from thermoelectricity to magnetism, with the vast majority of the members exhibiting metallic behavior. In this study, we synthesized a new group of materials with Cu-Si and Cu-Zn-Si square nets with the general formula BaCu1.33Si0.67P2 and BaCu2-(x+y)ZnxSiyP2 (0 ≤ x ≤ 0.9; 0.3 ≤ y ≤ 0.7). Several synthesized compounds are charge-balanced semiconductors, which are rare in the ThCr2Si2 family. All the reported compounds crystallize in the ThCr2Si2-type tetragonal I4/mmm space group, with Cu/Zn/Si jointly occupying the same 4d crystallographic site. In the Zn-free composition, BaCu1.33Si0.67P2, Ba, and P each occupy a single crystallographic site. The introduction of Zn results in the expansion of the unit cell and splitting the Ba atomic sites along the [001] direction. Such structural displacement of the Ba atoms was confirmed by the heat capacity measurements. Band structure and density-of-states calculations on ordered hypothetical structural models reveal either a small bandgap (∼0.2 eV) or semimetallic band structures. The compounds reported here exhibit high Seebeck coefficients and ultralow thermal conductivity, making them promising candidates for the development of thermoelectric materials.

Two-dimensional (2D) magnetic materials with exotic magnetic properties have garnered significant interest due to their potential applications in spintronics and data storage technologies. However, the limited availability of intrinsic 2D magnetic materials has driven efforts to induce and manipulate magnetism in otherwise nonmagnetic 2D systems through approaches such as chemical intercalation, defect engineering, and substitutional doping. Herein, we present a facile, chimie douce method for incorporating 3d transition metals (Cr, Co, and Ni) into the nonmagnetic PtSe2 sublattice. This synthetic approach enables control over layer thickness of Pt1-xMxSe2 (M = Cr, Co, Ni) nanosheets by varying the M identity and annealing conditions. Comprehensive scattering and spectroscopic characterizations confirm the successful and homogeneous substitution of M atoms at the Pt site, rather than intercalation, and reveal a strong correlation between nanosheet thickness and the identity of the substituting metal. High-temperature annealing of the nanosheets promotes an irreversible transformation toward the bulk phase, allowing for detailed characterization of structural and magnetic properties. A case study of Pt0.8Cr0.2Se2 reveals that nanosheet thickness plays a critical role in modulating local magnetic interactions. While Cr atoms in the as-synthesized few-layers-thick nanosheets exhibit predominantly short-range antiferromagnetic interactions, the emergence of short-range ferromagnetic exchange is revealed in the bulk material. Detailed ac susceptibility and remanent magnetization measurements further demonstrate that bulk Pt0.8Cr0.2Se2 adopts a frustrated magnetic ground state with clear signatures of ferromagnetic cluster-glass behavior. The systematic investigation presented herein establishes a clear and robust protocol for the synthesis and in-depth characterization of 2D transition-metal-substituted PtSe2 materials with varying layer thickness and paves a path toward their realization in spintronic and magnetic device applications.

Lithium thioborates, despite their potential cost-effectiveness and low density, have received considerably less attention as solid electrolytes compared to their thiophosphate counterparts. A primary obstacle to their widespread investigation has been the inherent challenge in synthesizing single-phase materials. Computational studies have predicted several lithium thioborate phases exhibiting high ionic conductivity, with Li9B19S33 notably predicted to reach 80 mS cm-1. However, experimental validation of these theoretical predictions remains absent. This work addresses this gap by detailing a successful synthesis of the previously elusive Li9B19S33 phase, facilitated by in situ temperature dependent powder X-ray diffraction. Our findings reveal the peritectic nature of phase formation, necessitating an excess of boron sulfide in the reaction mixture. We further present a comprehensive structural characterization of Li9B19S33 utilizing spectroscopic techniques like NMR, FT-IR, and diffuse reflectance and report on its ionic conductivity. Solid-state 6Li NMR line narrowing experiments revealed an ion mobility activation energy of 0.26 eV whereas activation energies derived from impedance spectroscopy measurements were significantly higher, resulting in lower than theoretically predicted ionic conductivity.

The synthesis, structures, and properties of two quaternary barium-arsenide materials are presented. The first, Ba4Ag2.3In1.7As8, is a novel material with the monoclinic unit cell (P21/m space group). The layered crystal structure of Ba4Ag2.3In1.7As8 may be considered a lower-symmetry, distorted analog of the LaCuSb2 structure. The structure features a rare As fragment, cis-trans As chains along the [010] direction. Large crystals of Ba4Ag2.3In1.7As8 can be grown from Bi flux and are used for subsequent transport property measurements. Electrical resistivity and heat capacity properties are reported, establishing Ba4Ag2.3In1.7As8 as a metallic phase. The second material, Ba4AgGa5As8, is a 3D material that crystallizes in the orthorhombic unit cell (noncentrosymmetric and polar Iba2 space group). Expanding upon its original discovery, the optimized synthetic profile for single-phase polycrystalline samples as well as transport properties relevant to thermoelectric applications are presented. Ba4AgGa5As8 exhibits a high Seebeck coefficient of 290 mu V K-1 at room temperature, indicative of lower carrier concentrations typical for nonmetallic phases. Electrical resistivity measurements also affirm conventional semiconducting behavior for Ba4AgGa5As8.

Mixed-valent Cu hybrid inorganic–organic frameworks exhibit high structural flexibility and allow for the inclusion of magnetic and optically-active 2D components into their host structures.

The discovery of Zintl compounds remains a powerful strategy for identifying materials with tunable electronic and thermal transport properties. During a concerted search for new inorganic clathrates with In-Sb frameworks, we discovered BaIn4Sb4. The composition of this phase deviates from that expected for a type-I clathrate with tetrahedral coordination of all In and Sb atoms (Ba8In31Sb15). Instead, in the chiral structure of BaIn4Sb4 (space group P3121, No. 152), a part of the In atoms have a trigonal planar coordination of 1In + 2Sb, forming Sb2-In-In-Sb2 nonplanar fragments isostructural to diborane(4) B2H4 with D 2d symmetry. Ba atoms are located inside 16-vertex In8Sb8 polyhedra, which share vertices and edges to form a chiral framework around the 31 screw axes. The title compound is electron-balanced, [Ba2+][In2+]2[In3+]2[Sb3-]4, which was confirmed by characterization of the charge and heat transport properties. BaIn4Sb4 exhibits a low thermal conductivity and high Seebeck coefficient, suggesting its untapped potential for thermoelectric applications. Density functional theory (DFT) calculations indicate that chemical doping may enhance carrier concentration and improve the originally low electrical conductivity, thus enhancing thermoelectric performance.

The low-temperature modification of beta-Ag2Se has proven to be useful as a near-room-temperature thermoelectric material. Over the past years, research has been devoted to interstitial, vacancy, and substitutional doping into the parent beta-Ag2Se structure, aiming at tuning the material's charge and heat transport properties to enhance thermoelectric performance. The transformation of beta-Ag2Se into alpha-Ag2Se at similar to 134 degrees C and the low solubility of dopants are the main obstacles for the doping approach. Herein, we report a facile, safe, scalable, and cost-effective benchtop approach to successfully produce metal-doped beta-Ag2Se. The doped materials display a remarkable enhancement of thermoelectric performance with a record-high peak zT of 1.30 at 120 degrees C and an average zT of similar to 1.15 in the 25-120 degrees C range for 0.2 at. % Zn-doped Ag2Se. The enhancement in zT is attributed to point defects created by Zn doping into Ag vacancies/interstitials, which enhances the scattering of phonons and tunes the charge carrier properties, leading to the significant suppression of thermal conductivity. The simplicity of the synthetic method developed herein and the high performance of the final products provide an avenue to produce high-quality Ag2Se-based thermoelectric materials.

Iron phosphide (Fe2P) crystallizes in its own hexagonal crystal structure type (h-Fe2P). As found in meteorites, orthorhombic polymorph (o-Fe2P) was originally reported as a high-temperature and high-pressure phase. Recently, o-Fe2P was described as being stable at ambient pressure, yet no synthetic methods were developed for single-crystal growth or single-phase bulk powder synthesis. Here, we report a successful method for growing o-Fe2P single crystals and synthesizing phase-pure polycrystalline samples using tin-flux. In situ powder X-ray diffraction studies showed that the phase transition from o-Fe2P to h-Fe2P occurs at about 873 K, and below that temperature, the formation of the o-Fe2P phase is favored thermodynamically rather than kinetically. Systematic comparison of transport, magnetic, and electrocatalytic properties of both h-Fe2P and o-Fe2P phases showed a substantial impact of the crystal structure on properties. The orthorhombic structural distortion resulted in considerable changes in magnetic properties, with the o-Fe2P phase exhibiting a 60% lower Fe magnetic moment and a substantially higher ferromagnetic Curie temperature than h-Fe2P. Electrochemical measurements toward the hydrogen evolution reaction in acidic media showed that the o-Fe2P phase requires an 80 mV lower overpotential than the h-Fe2P phase to generate a current density of -10 mA/cm(2), and their electronic structures suggest that the higher density of states at the Fermi energy is the origin of superior catalytic activity in o-Fe2P.

The type I clathrate, Ba8Cu16As30, is reinvestigated and found to have a low-temperature polymorph mP108-Ba8Cu16As30 with ordered Cu and As sites. In situ temperature-dependent powder X-ray diffraction experiments guided synthetic efforts toward the synthesis of the ordered monoclinic (mP108) and disordered cubic (cP54) polymorphs with high phase purity. While a transition from mP108-Ba8Cu16As30 to cP54-Ba8Cu16As30 is not directly observed, cP54-Ba8Cu16As30 is stabilized through quenching from high temperatures and is confirmed through high-resolution synchrotron powder X-ray diffraction. Combined theoretical predictions and experimental observations of the thermoelectric properties of both polymorphs reveal that the ordering of Cu and As atoms in the clathrate framework simultaneously enhances the Seebeck coefficient and electronic conductivity by increasing the hole effective mass and reducing the electronic scattering events. Consequently, the zT of mP108-Ba8Cu16As30 reaches a maximum of 0.2 at 575 K, an order of magnitude higher than that of cP54-Ba8Cu16As30.