Metal-rich Borides Research Articles

Fe- and B-Chains in the Ti5-xFe1-yOs6+x+yB6 Structure Type Derived from Chemical Twinning of the Nb1-xOs1+xB Type: Experimental and Computational Investigations.

The complex metal-rich boride Ti5-xFe1-yOs6+x+yB6 (0 < x,y < 1), crystallizing in a new structure type (space group Cmcm, no. 63), was prepared by arc-melting. The new structure contains both isolated boron atoms and zigzag boron chains (B-B distance of 1.74 Å), a rare combination among metal-rich borides. In addition, the structure also contains Fe-chains running parallel to the B-chains. Unlike in previously reported structures, these Fe-chains are offset from each other and arranged in a triangular manner with intrachain and interchain distances of 2.98 and 6.69 Å, respectively. Density functional theory (DFT) calculations predict preferred ferromagnetic interactions within each chain but only small energy differences for different magnetic interactions between them, suggesting a potentially weak long-range order. This new structure offers the opportunity to study new configurations and interactions of magnetic elements for the design of magnetic materials.

Nickel Boride (NixB) Nanocrystals: From Solid-State Synthesis to Highly Colloidally Stable Inks

Metal borides, a class of materials intensively used in industry as superconductors, magnetic materials, or hot cathodes, remain largely unexplored at the nanoscale mainly due to the difficulty in synthesizing single-phase nanocrystals. Recent works have shown that synthetic methods at lower temperatures (<400 °C) yield amorphous polydisperse nanoparticles, while phase purity is an issue at higher temperatures. Among all the metal-rich borides, nickel borides (NixB) could be a potential catalyst for a broad range of applications (hydrogenations, electrochemical hydrogen, and oxygen evolution reactions) under challenging conditions (such as high pH or high temperatures). Here, we report a novel solid-state method to synthesize NixB nanopowders (with a diameter of approximately 45 nm) and their conversion into colloidal suspensions (inks) through treatment of the nanocrystal surface. For the solid-state synthesis, we used commercially available salts and explored the reaction between the Ni and B sources while varying the synthetic parameters under mild and solvent-free reaction conditions. We show that pure phase Ni3B and Ni2B NCs can be obtained with high yield in the pure phase using as precursors NiCl2 and Ni, respectively. Through extensive mechanistic studies, we show that Ni nanoclusters (1–2 nm) are an intermediate in the boriding process, while the metal co-reactant lowers the decomposition temperature of NaBH4 (used as a reducing agent and B source). Size control can instead be exerted through reaction mediators, as seen from the differential nucleation and growth of Ni (clusters) or NixB NCs when employing L- (amine, phosphine) and X-type (carboxylate) mediators. Applying surface engineering methods to our NixB NCs, we stabilized them with inorganic (NOBF4) or organic (borane tert-butyl amine, oleylamine) ligands in the appropriate solvent (DMSO, hexane). With this method, we produce stable inks for further solution processing applications. Our results provide tools for further development of catalysts based on NixB NCs and pave the way for synthesizing other metal boride colloidal nanostructures.

Transformation of trigonal planar B4 into zigzag B4 units within the new boride series Ti2–xM1+x–δIr3+δB3 (x = 0.5 for M = V–Mn, x = 0 for M = Mn–Ni and δ < 0.2)

In metal‒rich borides, numerous boron fragments Bn (n = 2, 3, 4, 5, 6) have been discovered, the B4 units being the most versatile with four different shapes (bent, zigzag, trigonal planar and tetrahedral). We report on the new boride series Ti2-xM1+x–δIr3+δB3 (x = 0.5 for M = V–Mn, x = 0 for M = Mn–Ni and δ < 0.2), in which a structural change occurs by successive substitution of the 3d transition metal M = V, Cr, Mn, Fe, Co and Ni. It is found that the change in structure from the Ti1+xOs2‒xRuB2‒type structure (P6‾2m, no. 189) to the Ti1+xRh2‒x+yIr3‒yB3‒type (Pbam, no. 55) leads to a change of B4 shape from trigonal planar B4 (M = V–Mn) to zigzag B4 fragment (M = Mn–Ni). Even though there is no group‒subgroup relationship between the two structures, we present how the Ti1+xOs2‒xRuB2‒type structure can easily be geometrically derived from the Ti1+xRh2-x+yIr3-yB3‒type.

A Delicate Balance between Antiferromagnetism and Ferromagnetism: Theoretical and Experimental Studies of A2 MRu5 B2 (A=Zr, Hf; M=Fe, Mn) Metal Borides.

Metal-rich borides with the Ti3 Co5 B2 -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 A2 MRu5 B2 (A=Zr, Hf, M=Fe, Mn) are presented. Total energy calculations show that the phases Zr2 FeRu5 B2 and Hf2 FeRu5 B2 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 Zr2 MnRu5 B2 and for FM in Hf2 MnRu5 B2 . 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.

Tuning the magnetic and structural properties of a three-metal boride alloy: Mn0.95−δFe1.05+δ−xCoxB

We present a comprehensive study of the three-metal boride alloys Mn0.95−δFe1.05 + δ−xCoxB (δ=0−0.15 and x=0−1.05) synthesized via arc melting and annealing. The alloys crystallize in a body-centered tetragonal unit cell in the same space group (I4/mcm) as the parent compound Mn2B. A small amount of MB (M = Mn, Fe, Co) impurity forms in the as-cast samples which is removed by acid treatment. Rietveld refinement on the powder X-ray data reveals an anisotropic variation of lattice parameters in the series. The c-axis increases with increasing Co content but the a-axis decreases. Magnetic measurements show a non-monotonic variation of both Tc and the saturated magnetization Ms as a function of x. These findings highlight the tunable nature of Mn0.95−δFe1.05 + δ−xCoxB and motivate further studies of metal-rich boride alloys.

New ternary tantalum borides containing boron dumbbells: Experimental and theoretical studies of Ta2OsB2 and TaRuB

The new ternary transition metal-rich borides Ta2OsB2 and TaRuB have been successfully synthesized by arc-melting the elements in a water-cooled crucible under an argon atmosphere. The crystal structures of both compounds were solved by single-crystal X-ray diffraction and their metal compositions were confirmed by EDX analysis. It was found that Ta2OsB2 and TaRuB crystallize in the tetragonal Nb2OsB2 (space group P4/mnc, no. 128) and the orthorhombic NbRuB (space group Pmma, no. 51) structure types with lattice parameters a=5.878(2)Å, c=6.857(2)Å and a=10.806(2)Å, b=3.196(1)Å, c=6.312(2)Å, respectively. Furthermore, crystallographic, electronic and bonding characteristics have been studied by density functional theory (DFT). Electronic structure relaxation has confirmed the crystallographic parameters while COHP bonding analysis indicates that B2-dummbells are the strongest bonds in both compounds. Moreover, the formation of osmium dumbbells in Ta2OsB2 through a Peierls distortion along the c-axis, is found to be the origin of superstructure formation. Magnetic susceptibility measurements reveal that the two phases are Pauli paramagnets, thus confirming the theoretical DOS prediction of metallic character. Also hints of superconductivity are found in the two phases, however lack of single phase samples has prevented confirmation. Furthermore, the thermodynamic stability of the two modifications of AMB (A=Nb, Ta; M =Ru, Os) are studied using DFT, as new possible phases containing either B4- or B2-units are predicted, the former being the most thermodynamically stable modification.

Metal-Rich Transition Metal Diborides as Electrocatalysts for Hydrogen Evolution Reactions in a Wide Range of pH

Solid solutions of HfB2-ZrB2 mixtures were prepared by high-energy ball milling of diboride and additive powders followed by spark plasma sintering (SPS). A mixture of stoichiometric 1:1 HfB2-ZrB2 borides was the base composition to which Hf, Zr, Ta, LaB6 or Gd2O3 was added. Hf, Zr and Ta were added in order to bring the boron-to-metal ratio down to 1.86, rendering the boride as MeB1.86. In the case of LaB6 and Gd2O3, 1.8 mol% was added. Electroanalytical behavior of hydrogen evolution reactions was evaluated in 1 M H2SO4 and 1 M NaOH solutions. The LaB6 additive material showed Tafel slopes of 125 and 90 mV/decade in acidic and alkaline solutions respectively. The Hf and Zr rich samples showed Tafel slopes of about 120 mV/decade in both electrolytes. The overpotentials of hydrogen evolution reactions (at 10 mA/cm2) in the alkaline solution were about 100 mV lower than those in acidic solution. The metal-rich diborides and addition of LaB6 showed better hydrogen evolution reaction (HER) activities than the base 1:1 HfB2-ZrB2 stoichiometric diboride solid solution. The higher activity of metal-rich borides could be attributed to the increased electron population at the d-orbitals of the metal shown by band structure modeling calculations using the Density Functional Theory approach.

AlPd15B7: a new superconducting cage-compound with an anti-Yb3Rh4Sn13-type of structure.

A new intermetallic compound AlPd15B7 was synthesized by arc-melting the stoichiometric mixture of the elements. Single crystal X-ray diffraction data of ternary metal-rich boride reveal a new type of structure with the space group Ia3d and the lattice parameter a = 16.4466(3) Å. It adopts a filled anti-Yb3Rh4Sn13-type structure, where the positions corresponding to 3Yb, 4Rh and 13Sn atoms are occupied by 3Pd, 4B, and 1Al + 12 Pd, respectively and 3B additionally at interstitial sites. Magnetic susceptibility, electrical resistivity, and specific heat measurements reveal bulk superconductivity with a critical temperature Tc ≈ 2.9 K. Electronic structure calculations show that Pd 4d and B 2p states dominate the density of states (DOS) at the Fermi level EF.

Fragment-Based Design of NbRuB as a New Metal-Rich Boride Superconductor

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTFragment-Based Design of NbRuB as a New Metal-Rich Boride SuperconductorWeiwei Xie, Huixia Luo, Kristen Baroudi, Jason W. Krizan, Brendan F. Phelan, and Robert J. Cava*View Author Information Department of Chemistry, Princeton University, Princeton, New Jersey 08540, United States*E-mail: [email protected]Cite this: Chem. Mater. 2015, 27, 4, 1149–1152Publication Date (Web):January 27, 2015Publication History Received4 December 2014Revised25 January 2015Published online5 February 2015Published inissue 24 February 2015https://doi.org/10.1021/cm504449sCopyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1061Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (2 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Crystal structure,Heat capacity,Superconducting transition,Superconductivity,Superconductors Get e-Alerts

Electronic, structural and magnetic studies of niobium borides of group 8 transition metals, Nb2MB2 (M=Fe, Ru, Os) from first principles calculations

The Nb2FeB2 phase (U3Si2-type, space group P4/mbm, no. 127) is known for almost 50 years, but until now its magnetic properties have not been investigated. While the synthesis of Nb2OsB2 (space group P4/mnc, no. 128, a twofold superstructure of U3Si2-type) with distorted Nb-layers and Os2-dumbbells was recently achieved, “Nb2RuB2” is still not synthesized and its crystal structure is yet to be revealed. Our first principles density functional theory (DFT) calculations have confirmed not only the experimental structures of Nb2FeB2 and Nb2OsB2, but also predict “Nb2RuB2” to crystalize with the Nb2OsB2 structure type. According to chemical bonding analysis, the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic M–B, B–Nb and M–Nb bonds (M=Fe, Ru, Os) are also found. These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of these ternary borides. The density-of-states at the Fermi level predicts metallic behavior, as expected, from metal-rich borides. Analysis of possible magnetic structures concluded preferred antiferromagnetic ordering for Nb2FeB2, originating from ferromagnetic interactions within iron chains and antiferromagnetic exchange interactions between them.

Nb2OsB2, with a new twofold superstructure of the U3Si2 type: Synthesis, crystal chemistry and chemical bonding

The new ternary metal-rich boride, Nb 2 OsB 2 , was synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The compound was characterized from single-crystal X-ray data and EDX measurements. It crystallizes as a new superstructure (space group P 4/ mnc , no. 128) of the tetragonal U 3 Si 2 -structure type with lattice parameters a =5.922(1) Å and c =6.879(2) Å. All of the B atoms are involved in B 2 dumbbells with B–B distances of 1.89(4) Å. Structure relaxation using VASP (Vienna ab intio Simulation Package) has confirmed the space group and the lattice parameters. According to electronic structure calculations (TB–LMTO–ASA), the homoatomic B–B interactions are optimized and very strong, but relatively strong heteroatomic Os–B, Nb–B and Nb–Os bonds are also found: These interactions, which together build a three-dimensional network, are mainly responsible for the structural stability of this new phase. The density of state at the Fermi level predicts metallic behavior, as expected, from this metal-rich boride. Nb 2 OsB 2 is, to the best of our knowledge, the first fully characterized phase in the ternary Nb–Os–B system. It crystallizes (space group P 4/ mnc , 128) with a new twofold superstructure of the U 3 Si 2 structure type (space group P 4/ mbm , 127), and is therefore the first boride in this structure family crystallizing with a superstructure of the U 3 Si 2 structure type. We show that the distortions leading to this superstructure occurs mainly in the Nb-layer, which tries to accommodate the large osmium atoms. The consequence of this puckering is the building osmium dumbbells instead of chains along [001]. • First compound in the Nb–Os–B system. • New twofold superstructure of U 3 Si 2 structure type. • Puckering of Nb-layer responsible for superstructure occurrence. • Chemical bonding studied by density functional theory.

Editors' Choice: ChemInform 19/2013

ChemInformVolume 44, Issue 19 Editors' ChoiceFree Access Editors' Choice: ChemInform 19/2013 First published: 18 April 2013 https://doi.org/10.1002/chin.201391902AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. References Ibrahim M. Ndassa, Michael Gillessen, Boniface P. T. Fokwa, Electronic Structure, Chemical Bonding and Magnetism of the Metal-Rich Borides MRh6B3 (M: Cr, Mn, Fe, Co, Ni) with Th7Fe3-Type Structure: A Density Functional Theory Study., Solid State Sci., 2013, 17, 14– 20. DOI: 10.1016/j.solidstatesciences.2012.12.005; Volume44, Issue19May 7, 2013 ReferencesRelatedInformation

Index of Classification Terms: ChemInform 19/2013

ChemInformVolume 44, Issue 19 Index of Classification TermsFree Access Index of Classification Terms: ChemInform 19/2013 First published: 18 April 2013 https://doi.org/10.1002/chin.201319282AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat References Ibrahim M. Ndassa, Michael Gillessen, Boniface P. T. Fokwa, Electronic Structure, Chemical Bonding and Magnetism of the Metal-Rich Borides MRh6B3 (M: Cr, Mn, Fe, Co, Ni) with Th7Fe3-Type Structure: A Density Functional Theory Study., Solid State Sci., 2013, 17, 14– 20. DOI: 10.1016/j.solidstatesciences.2012.12.005; Volume44, Issue19May 7, 2013 ReferencesRelatedInformation

Electronic structure, chemical bonding and magnetism of the metal-rich borides MRh6B3 (M = Cr, Mn, Fe, Co, Ni) with Th7Fe3-type structure: A density functional theory study

The electronic structures, magnetic properties and chemical bonding of MRh6B3 (M = Cr, Mn, Fe, Co, Ni) were analyzed theoretically by first-principles density functional theory. All functionals used correctly reproduced the magnetic state of all experimentally characterized phases MRh6B3 (M = Cr, Fe, Co, Ni). In addition, ferromagnetic ordering is predicted in MnRh6B3, which is yet to be synthesized and characterized, with a magnetic saturation moment predicted to lie between 3.55 μB (LDA) and 4.07 μB (GGA). Linear muffin tin orbital (LMTO) calculations were applied to study the chemical bonding and magnetism in all phases. These calculations show that the Rh–B contacts are responsible for the structural stability, while the Rh–M interactions influence the magnetic behavior, whereas the M–B interactions regulate the variation of the unit cell volume in the series. The non-vanishing DOS values at all Fermi levels suggest metallic character for all phases as expected for these intermetallic compounds.

Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Crx(Rh1−yRuy)7−xB3 (x=0.88–1; y=0–1) with Th7Fe3-type structure

Powder samples and single crystals of the new complex boride series Crx(Rh1−yRuy)7−xB3 (x=0.88–1; y=0–1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region.

The complex metal-rich boride Ti1+xRh2−x+yIr3−yB3 (x=0.68, y=1.06) with a new structure type containing B4 zigzag fragments: Synthesis, crystal chemistry and theoretical calculations

Polycrystalline samples and single crystals of the new complex boride Ti1+xRh2−x+yIr3−yB3 (x=0.68; y=1.06) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-Ray diffraction as well as EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase, which represents a new structure type containing trans zigzag B4 fragments as well as isolated boron atoms crystallizes in the orthorhombic space group Pbam (Nr. 55) with the lattice parameters a=8.620(1)Å, b=14.995(2)Å and c=3.234(1)Å. First-principles density functional theory calculations using the Vienna ab-initio simulation package (VASP) were performed on an appropriate structural model (using a supercell approach) and the experimental crystallographic data could be reproduced accurately. Based on this model, the density of states and crystal orbital Hamilton population (for bonding analysis) were calculated, using the linear muffin-tin orbital atomic sphere approximation (LMTO-ASA) method. According to these calculations, this metal-rich compound should be metallic, as expected. Furthermore, very strong boron–boron interactions are observed in the trans zigzag B4 fragment, which induce a clear differentiation of two types of metal–boron contacts with different strength. The observed three-dimensional metal–metal interaction is in good agreement with the predicted metallic behavior.

Complete Titanium Substitution by Boron in a Tetragonal Prism: Exploring the Complex Boride Series Ti3−xRu5−yIryB2+x (0 ≤ x ≤ 1 and 1 &lt; y &lt; 3) by Experiment and Theory

Polycrystalline samples and single crystals of four members of the new complex boride series Ti(3-x)Ru(5-y)Ir(y)B(2+x) (0 ≤ x ≤ 1 and 1 < y < 3) were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere. The new silvery phases were structurally characterized by powder and single-crystal X-ray diffraction as well as energy- and wavelength-dispersive X-ray spectroscopy analyses. They crystallize with the tetragonal Ti(3)Co(5)B(2) structure type in space group P4/mbm (No. 127). Tetragonal prisms of Ru/Ir atoms are filled with titanium in the boron-poorest phase (Ti(3)Ru(2.9)Ir(2.1)B(2)). Gradual substitution of titanium by boron then results in the successive filling of this site by a Ti/B mixture en route to the complete boron occupation, leading to the boron-richest phase (Ti(2)Ru(2.8)Ir(2.2)B(3)). Furthermore, both ruthenium and iridium share two sites in these structures, but a clear Ru/Ir site preference is found. First-principles density functional theory calculations (Vienna ab initio simulation package) on appropriate structural models (using a supercell approach) have provided more evidence on the stability of the boron-richest and -poorest phases, and the calculated lattice parameters corroborate very well with the experimentally found ones. Linear muffin-tin orbital atomic sphere approximation calculations further supported these findings through crystal orbital Hamilton population bonding analyses, which also show that the Ru/Ir-B and Ru/Ir-Ti heteroatomic interactions are mainly responsible for the structural stability of these compounds. Furthermore, some stable and unstable phases of this complex series could be predicted using the rigid-band model. According to the density of states analyses, all phases should be metallic conductors, as was expected from these metal-rich borides.

Synthesis, Crystal Chemistry and Magnetism of the Metal-rich Borides MxRh7-xB3 (M = Cr, Mn, Ni; x = 0.39 - 1) with Th7Fe3-type Structure

Synthesis, Crystal Chemistry and Magnetism of the Metal-rich Borides MxRh7-xB3 (M = Cr, Mn, Ni; x = 0.39 - 1) with Th7Fe3-type Structure

Molecular Models of Solid State Metal Boride Structures

Based on existing connections between borane cages and boron-rich metal borides on the one hand and metal clusters containing boron atoms and metal-rich borides on the other, selected metallaboranes of intermediate stoichiometry are investigated as models for transition metal borides with similar M/B ratios. This study is possible due to the recent development of a general route to metallaboranes for group 5–9 metals that permits the distinct role of the transition metal in metallaborane cluster bonding to be revealed. The comparison shows that it is MM and MB covalent bonding rather than M and B electronic charges that drives change in structure with metal identity.

The first trigonal prismatic discrete transition-metal boride cluster: preparation and molecular structure of [PPN][Ru6(H)2(CO)18B][PPN =(Ph3P)2N+

The reaction of [PPN][Ru3(CO)9B2H5] with [Ru3(CO)10(NCMe)2] leads to two borido clusters: [PPN][Ru6(H)2(CO)18B], [PPN][1], and [PPN][Ru6(CO)17B], [PPN][2]; complex 1 the structure of which has been confirmed crystallographically, is the first example of an interstitial boron atom encapsulated within a trigonal prismatic transition-metal cage and provides a useful model for a bulk metal-rich boride.