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Abstract: Polycrystalline samples of the boride series Ti9−x M2+x Ru18B8 (M=Cr, Co, Mn, Ni) including single crystals of Ti8Co3Ru18B8 have been prepared by arc-melting the elements. The phases were characterized by powder X-ray diffraction (Rietveld refinement), single-crystal X-ray diffraction (for M=Co), and energy-dispersive X-ray (EDX) analysis. They are substitutional variants of the Zn11Rh18B8 structure type, space group P4/mbm (No. 127) and contain a “scaffold” structural unit (M-ladders interacting with M/Ti-chains) as well as isolated M/Ti-chains. According to DFT calculations, the Ru–X (X=B, Ti, Ti/M) bonding interactions are nearly constant throughout the series and responsible for the structural stability of these phases, whereas the M–M and Ru–M interactions vary significantly with varying valence electron count. Furthermore, density of states (DOS) analyses predict the phases with M=Mn and Ni to develop a total magnetic moment but not the M=Co phase. Susceptibility measurements confirm the Co phase to be paramagnetic and the Mn Phase orders ferrimagnetically below 120K and thus develops a magnetic moment, as predicted. [Copyright &y& Elsevier]

Polycrystalline samples and single crystals of the new metal-rich boride V1+ xNb1- xIrB2 ( x ≈ 0.1), were synthesized by arc-melting the elements in a water-cooled copper crucible under an argon atmosphere and characterized by X-ray diffraction and EDX measurements. The crystal structure was refined on the basis of single crystal data. The new phase adopts the Mo2IrB2-type structure (space group Pnnm, no. 58) with the lattice parameters a = 7.301(7) Å, b = 9.388(9) Å and c = 3.206(5) Å. It is the first quaternary representative of Mo2IrB2-type structure. The structure contains zigzag B4-fragments with boron-boron distances of 1.83-1.85 Å. The electronic 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 zigzag B4-fragment and two significantly different Ir-B interactions are observed in the new phase and the prototype Mo2IrB2. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline samples and single crystals of the new complex boride Ti1+x Rh2−x+y Ir3−y B3 (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. [Copyright &y& Elsevier]

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]