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The novel composition – TiFe1.3Os3.9B2.8 – is the first quaternary phase of the NbRuB structure type. The layer‐like structure consists of boron (mixed with 8 % Fe) dumbbells in the same layer as osmium atoms, some sites with mixed occupancies. The second layer has isolated boron, osmium/titanium (51 % Os) and iron atoms. The presence of iron enables the study of magnetism as Fe‐chains are present, with intra‐ and interchain distances of 3.02 Å and 5.76 Å, respectively. Density functional theory (DFT) predicts magnetic ordering to be likely with the antiferromagnetic ground state only 13 meV more favorable than the ferromagnetic state. This discovery opens the possibilities of studying various quaternary compositions in the superconducting NbRuB structure type. [ABSTRACT FROM AUTHOR]

The structural parameters, chemical bonding and magnetic properties of the ternary boride series M1.5Rh5.5B3 (M = Cr, Mn, Fe, Co, Ni) were investigated by first principles DFT calculations. The calculated crystallographic lattice parameters corroborate well with the experimental results of the reported Fe1.3Rh5.7B3 single crystal. In the most stable structural model used, Fe-dumbbells as well as isolated Fe-atoms exist. From spin polarised calculations, ferromagnetism is found for the members with M = Fe, Co, while ferrimagnetism is more stable for Mn1.5Rh5.5B3 and Pauli paramagnetism is more stable for M = Cr, Ni. The total magnetic moment per formula unit for the M = Mn, Fe and Co phases is calculated to be 3.32, 5.00 and 3.26 μB, respectively. According to COHP chemical bonding analysis, Rh-B contacts are mainly responsible for the structural stability, while Rh-M interactions influence the magnetic behavior of these complex borides. [ABSTRACT FROM AUTHOR]

Polycrystalline samples and single crystals of the complex boride Ti9Fe2Ru18B8 were synthesized by arc-melting the elements and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray analysis. Ti9Fe2Ru18B8 is a new substitutional variant of the Zn11Rh18B8 structure type, space group P4/mbm (No. 127), whose remarkable feature is that it contains one-dimensional chains of dumbbells of magnetically active Fe atoms, which form "ladders" along the c axis. The Fe-Fe distance within a dumbbell is 2.489(2) Å, and the Fe2-Fe2 distance between two dumbbells is 2.968(1) Å; in contrast, the chains are well-separated from each other by distances of at least 11.217(2) Å. According to the results of tight-binding electronic structure calculations, Ru-B and Ti-Ru contacts are responsible for the structural robustness, while Fe-Fe interactions influence the magnetic behavior, According to magnetization measurements, Ti9Fe2Ru18B8 orders ferromagnetically between 10 and 200 K. A model for ferromagnetism in this ladder-based structure identifies ferromagnetic coupling among neighboring spin-triplet Fe2 dimers along the c axis as the origin of the magnetic behavior. [ABSTRACT FROM AUTHOR]

A new ternary phase, TiIrB, was synthesized by arc-melting of the elements and characterized by powder X-ray diffraction. The compound crystallizes in the orthorhombic Ti1+xRh2−x+yIr3−yB3 structure type, space group Pbam (no. 55) with the lattice parameters a = 8.655(2), b = 15.020(2), and c = 3.2271(4) Å. Density Functional Theory (DFT) calculations were carried out to understand the electronic structure, including a Bader charge analysis. The charge distribution of TiIrB in the Ti1+xRh2−x+yIr3−yB3-type phase has been evaluated for the first time, and the results indicate that more electron density is transferred to the boron atoms in the zigzag B4 units than to isolated boron atoms. [ABSTRACT FROM AUTHOR]

The quinary members in the solid solution Hf2Fe1−δRu5−xIrx+δB2 (x=1–4, VE=63–66) have been investigated experimentally and computationally. They were synthesized via arc‐melting and analyzed by EDX and X‐ray diffraction. Density functional theory (DFT) calculations predicted a preference for magnetic ordering in all members, but with a strong competition between ferro‐ and antiferromagnetism arising from interchain Fe−Fe interactions. The spin exchange and magnetic anisotropy energies predicted the lowest magnetic hardness for x=1 and 3 and the highest for x=2. Magnetization measurements confirm the DFT predictions and demonstrate that the antiferromagnetic ordering (TN=55–70 K) found at low magnetic fields changed to ferromagnetic (TC=150–750 K) at higher fields, suggesting metamagnetic behavior for all samples. As predicted, Hf2FeRu3Ir2B2 has the highest intrinsic coercivity (Hc=74 kA/m) reported to date for Ti3Co5B2‐type phases. Furthermore, all coercivities outperform that of ferromagnetic Hf2FeIr5B2, indicating the importance of AFM interactions in enhancing magnetic anisotropy in these materials. Importantly, two members (x=1 and 4) maintain intrinsic coercivities in the semi‐hard range at room temperature. This study opens an avenue for controlling magnetic hardness by modulating antagonistic AFM and FM interactions in low‐dimensional rare‐earth‐free magnetic materials. [ABSTRACT FROM AUTHOR]

The ternary borides Ta3Ru5B2, Zr2.86Ru5.14B2, and Hf2.83Ru5.17B2 are synthesized by arc-melting of stoichiometric mixtures of the elements (Ar, Cu crucibles). [ABSTRACT FROM AUTHOR]

We present the first bulk synthesis of Ti3Co5B2, which was realized by arc-melting a Co-rich elemental mixture. Our X-ray diffraction studies revealed a Ti/Co mixed occupancy on one of two possible Ti sites suggesting a phase width with x = 0-0.52 in Ti3- xCo5+ xB2. Moreover, we studied experimentally and theoretically the isoelectronic substitution of Ti and Co by their respective higher homologues (Zr/Rh and Hf/Ir). Surprisingly, Ti3Co5B2-type phase was obtained only for the Hf/Ir combination (single crystal analysis of Hf3Ir5B2), whereas for Zr/Rh a perovskite-like phase (ZrRh3Bx) was discovered instead. We found that small but crucial differences (atomic radius ratio and electronegativity difference) between elements of the same group in the periodic Table are responsible for the unexpected trend deviation. This finding is supported by DFT calculations of the free energy of formation. [ABSTRACT FROM AUTHOR]

Powder samples and single crystals of the new ternary compound NbRuB were synthesized by arc-melting of the elements in a water-cooled crucible under an argon atmosphere. The samples have been characterized by X-ray diffraction and energy-dispersive X-ray spectroscopy (EDX) measurements. Furthermore, the crystallographic, electronic, and bonding characteristics have been studied by density functional theory. The title compound crystallizes with a new orthorhombic structure type in the space group Pmma (no. 51) with the lattice parameters a = 10.870(2) Å, b = 3.173(1) Å, and c = 6.350(2) Å. The structure consists of two kinds of atomic layers: the first layer (at y = 0) contains niobium atoms and isolated boron atoms, and the second (at y = 0.5) contains ruthenium atoms and boron dumbbells. Electronic structure relaxation has confirmed the crystallographic parameters, and crystal orbital Hamilton population (COHP) bonding analysis indicates that the B-B bond is the strongest bond, but the numerous and relatively strong metal-boron and Nb-Ru bonds are responsible for the overall stability and indicate a three-dimensional bonding character in the new compound. [ABSTRACT FROM AUTHOR]

The electronic structures of "Ti9-nFe2+nRu18B8" (n= 0, 0.5, 1, 2, 3); in connection to the recently synthesized Ti9-nFe2+n-RU18B8(n = 1, 2), have been investigated and analyzed using LSDA tight-binding calculations to elucidate the distribution of Fe and Ti, to determine the maximum Fe content, and to explore possible magnetic structures to interpret experimental magnetization results. Tbrough a combination of calculations on specific models and using tbe rigid band approximation, which is validated by the DOS curves for "T9-nFe2+nRu18B8" (n = 0, 0.5, 1, 2,3), mixing of Fe and Ti is anticipated at both tbe 2b- and 4h-chain sites. The model "Ti8.5Fe2.5Ru18B8" (n = 0.5) revealed that both Brewer-type Ti-Ru interactions as well as ligand field splitting ofthe Fe 3d orbitals regulated the observed valence electron counts between 220 and 228 electrons/formula unit. Finally, models of magnetic structures were created using "Ti6Fe5Ru18B8" (n = 3). A rigid band analysis of tbe LSDA DOS curves concluded preferred ferromagnetic ordering at low Fe content (n ⩽ 0.75) and ferrimagnetic ordering at higher Fe content (n > 0.75). Ferrimagnetism arises from antiferromagnetic exchange coupling in the scaffold of Fel-ladder and 4h-chain sites. [ABSTRACT FROM AUTHOR]

Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V3B4 have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H2SO4) increases with increasing boron chain condensation in vanadium borides: Using a −23 mV overpotential decrement derived from −0.296 mV (for VB at −10 mA cm−2 current density) and −0.273 mV (for V3B4) we accurately predict the overpotential of VB2 (−0.204 mV) as well as that of unstudied V2B3 (−0.250 mV) and hypothetical "V5B8" (−0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical VxBy phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships. [ABSTRACT FROM AUTHOR]

Transition‐metal borides (TMBs) have recently attracted attention as excellent hydrogen evolution (HER) electrocatalysts in bulk crystalline materials. Herein, we show for the first time that VB and V3B4 have high electrocatalytic HER activity. Furthermore, we show that the HER activity (in 0.5 m H2SO4) increases with increasing boron chain condensation in vanadium borides: Using a −23 mV overpotential decrement derived from −0.296 mV (for VB at −10 mA cm−2 current density) and −0.273 mV (for V3B4) we accurately predict the overpotential of VB2 (−0.204 mV) as well as that of unstudied V2B3 (−0.250 mV) and hypothetical "V5B8" (−0.227 mV). We then derived an exponential equation that predicts the overpotentials of known and hypothetical VxBy phases containing at least a boron chain. These results provide a direct correlation between crystal structure and HER activity, thus paving the way for the design of even better electrocatalytic materials through structure–activity relationships. [ABSTRACT FROM AUTHOR]

Metal‐rich borides with the Ti3Co5B2‐type structure represent an ideal playground for tuning magnetic interactions through chemical substitutions. In this work, density functional theory (DFT) and experimental studies of Ru‐rich quaternary borides with the general composition A2MRu5B2 (A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr2FeRu5B2 and Hf2FeRu5B2 prefer ground states with strong antiferromagnetic (AFM) interactions between ferromagnetic (FM) M‐chains. Manganese substitution for iron lowers these antiferromagnetic interchain interactions dramatically and creates a strong competition between FM and AFM states with a slight preference for AFM in Zr2MnRu5B2 and for FM in Hf2MnRu5B2. Magnetic property measurements show a field dependence of the AFM transition (TN): TN is found at 0.1 T for all phases with predicted AFM states whereas for the predicted FM phase it is found at a much lower magnetic field (0.005 T). Furthermore, TN is lowest for a Hf‐based phase (20 K) and highest for a Zr‐based one (28 K), in accordance with DFT predictions of weaker AFM interactions in the Hf‐based phases. Interestingly, the AFM transitions vanish in all compounds at higher fields (>1 T) in favor of FM transitions, indicating metamagnetic behaviors for these Ru‐rich phases. [ABSTRACT FROM AUTHOR]

Tuning of the magnetic properties of intermetallic materials is increasingly gaining interest in the chemistry community. We report on the successful synthesis and magnetic characterizations of the two new quaternary boride series MRh6- nRu nB3 (M = Co, Ni; 1 ≤ n ≤ 5). Powder samples have been synthesized by arc-melting the elements under purified argon in a water-cooled copper crucible. The products were characterized by powder X-ray diffraction through Rietveld refinements as well as EDX measurements. All phases crystallize in the hexagonal Th7Fe3 structure type (space group P63 mc, no. 186, Z = 2). In the Co-based series, the lattice parameters decrease linearly with increasing ruthenium content, whereas in the Ni-based series they remain nearly constant for the Rh-rich side then decrease with increasing Ru content. Significant ferromagnetic interactions are observed for the Co-based series, and they decrease linearly with increasing Ru content with magnetic moments decreasing from 0.74 µB (CoRh5RuB3) to 0.13 µB (CoRhRu5B3) at 5 K and 5 T. Pauli paramagnetism dominates the Ni-based series. [ABSTRACT FROM AUTHOR]

Molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo2B, α-MoB, β-MoB, and MoB2 by arc-melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X-ray photoelectron spectroscopy (XPS) for the first time; MoB2 and β-MoB show excellent activity in the same range as the recently reported α-MoB and β-Mo2C phases, while the molybdenum richest phase Mo2B show significantly lower HER activity, indicating a strong boron-dependency of these borides for the HER. In addition, MoB2 and β-MoB show long-term cycle stability in acidic solution. [ABSTRACT FROM AUTHOR]

Analysis of the electronic density of states of the hypothetical ternary double-perovskite-like phases "Sc2T6B (T = Ir, Pd, Ni)" reveals the presence of deep and large pseudogaps between 61 and 68 valence electrons (VE) as well as a strong peak at 69 VEs. Subsequently, crystal orbital Hamilton population (COHP) bonding analysis shows that the heteroatomic T--B and Sc--T interactions are optimized in Sc2Ir6B (63 VE) but not in "Sc2Pd6B (69 VE)" and "Sc2Ni6B (69 VE)", thus indicating less stability for these VE-richer phases. These findings point out the possibility of discovering new double-perovskite-like borides through chemical substitution and lead to the study of the Sc2Ir6-xPdxB and Sc2Ir6-xNixB (x = 0-6; VE = 63-69) series, for which powder samples and single crystals were synthesized by arc melting the elements. Superstructure reflections were observed in the powder diffractograms of Sc2Ir6-xPdxB and Sc2Ir6-xNixB for x = 0-5 and VE = 63-68, thereby showing that these phases crystallize in the double-perovskite-like Ti2Rh6B-type structure (space group Fm3m, Z = 4). Single-crystal and Rietveld refinement results confirm and extend these findings because Pd (or Ni) is found to mix exclusively with Ir in all quaternary compositions. For x = 6, no superstructure reflections were observed, in accordance with the theoretical expectation for the 69 VE phases. [ABSTRACT FROM AUTHOR]

Transition-metal borides show not only promising physical properties but also a rich variety of crystal structures. In this context, quantum-chemical tools can shed light on important facets of the chemistry within such intermetallic borides. Using density-functional theory (DFT), we analyze in detail two phases of significant structural-chemical importance: the recently synthesized Ti1+xOs2-xRuB2 and the isotypical Ti1+xOs3-xB2. Starting from the observation of different Ti/Os occupations in X-ray crystal structure analysis, we assess suitable computational models and rationalize how the interplay of Ti-Ti, Ti-Os, and Os-Os bonds drives the site preferences. Then, we move on to a systematic investigation of the metal-boron bonds which embed the characteristic, trigonal-planar B4 units within their metallic surroundings. Remarkably, the different Ti-B bonds in Ti1+xOs2-xRuB2 (and also in its ternary derivative) are of vastly different strength, and the strength of these bonds does not correlate with their length. The tools presented in this work are based on simple and insightful chemical arguments together with DFT, and may subsequently be transferred to other intermetallic phases-transition-metal borides and beyond. [ABSTRACT FROM AUTHOR]

Single-phase polycrystalline samples and single crystals of the complex boride phases Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 have been synthesized by arc melting the elements. The phases were characterized by powder and single-crystal X-ray diffraction as well as energy-dispersive X-ray analysis. They are new substitutional variants of the Zn11Rh18B8 structure type, space group P4/mbm (no. 127). The particularity of their crystal structure lies in the simultaneous presence of dumbbells which form ladders of magnetically active iron atoms along the [001] direction and two additional mixed iron/titanium chains occupying Wyckoff sites 4h and 2b. The ladder substructure is ca. 3.0 Å from the two chains at the 4h, which creates the sequence chain-ladder-chain, establishing a new structural and magnetic motif, the scaffold. The other chain (at 2b) is separated by at least 6.5 Å from this scaffold. According to magnetization measurements, Ti8Fe3Ru18B8 and Ti7Fe4Ru18B8 order ferrimagnetically below 210 and 220 K, respectively, with the latter having much higher magnetic moments than the former. However, the magnetic moment observed for Ti8Fe3Ru18B8 is unexpectedly smaller than the recently reported Ti9Fe2Ru18B8 ferromagnet. The variation of the magnetic moments observed in these new phases can be adequately understood by assuming a ferrimagnetic ordering involving the three different iron sites. Furthermore, the recorded hysteresis loops indicate a semihard magnetic behavior for the two phases. The highest Hc value (28.6 kA/m), measured for Ti7Fe4Ru18B8, lies just at the border of those of hard magnetic materials. [ABSTRACT FROM AUTHOR]

Keywords: antiferromagnetism; borides; density functional theory (DFT); ferromagnetism; Ti3Co5B2-type structure DFT calculations predict antiferromagnetism (AFM) in the Fe-based phases but competing ferromagnetism (FM) and antiferromagnetism in Mn-based ones. Antiferromagnetism, borides, density functional theory (DFT), ferromagnetism, Ti3Co5B2-type structure. [Extracted from the article]

Abstract: Invited for the cover of this issue is the group of Boniface Fokwa from the University of California, Riverside, USA. The cover image shows two boron fragments found in the modifications of NbOsB: a finite B4 fragment (left) and the infinite B‐chain (right) as typically found in borides with a smaller metal‐to‐boron ratio. [ABSTRACT FROM AUTHOR]

DFT calculations for the ternary phases Sc2M6B (M: Ir, Pd, Ni) reveal the presence of pseudogaps near their Fermi levels between 61 and 68 valence electrons leading to the prediction of new phases Sc2Ir6‐xPdxB and Sc2Ir6‐xNixB (x = 0—6) in the double‐perovskite‐like Ti2Rh6B‐type structure. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of the boride series Ti9-xM2+xRu18B8 (M: Cr, Co, Mn, Ni) and single crystals of Ti8Co3Ru18B8 are prepared by arc melting of the elements. [ABSTRACT FROM AUTHOR]