Heteronuclear double resonance on formamide-15N and ammonium-15N using weak perturbing radiofrequency fields

Weak radiofrequency fields have been used to perturb nitrogen transitions in the formamide-¹⁵N and ammonium-¹⁵N molecules. Observation of the proton spectra has completed the determination of the relative signs of the coupling constants in formamide-¹⁵N. Chemical shifts precisely related to tetramethylsilane are reported and a discussion of a method for presentation of shift results is included.     

Single crystal studies on boron-rich τ-borides Ni23−xMxB6 (M=Zn, Ga, In, Sn, Ir)—The surprising occurrence of B4-tetraheda as a normal case?

Single crystals of the cubic τ-borides Ni_23−xM_xB₆ (M=Zn, Ga, In, Sn, Ir) were synthesised from the elements at temperatures between 1200 and 1500 °C. The structure refinements show that the existence of boron-rich phases is quite common. Starting from the idealised composition Ni₂₀M′₃B₆ a part of the metal atoms on site 8c is substituted by B₄ tetrahedra. For M′=Ga a complete exchange seems to be possible leading to the composition Ni₂₀GaB₁₄. For M′=Zn and Sn the formation of solid solutions is less extended. For M′=In no exchange is observed but an unusual pattern of Ni/In distribution is observed. With M=Ir mixed occupations occur for all sites and the boron content varies, too. All compositions were confirmed by EDX measurements.     

Nickel Boride Catalyst in Organic Synthesis—The Effects of Promoters on Nickel Borides for Hydrogenation Reactions

Cr, Co and Rh were introduced into P-1, P-2 and P-2W nickel boride catalysts as promoters. The substrates of cyclohexanone and cyclohexene were used to examine the effects of those promoters on nickel borides for hydrogenation reactions. On cyclohexanone with strongly-polared carbonyl group, Cr, Co and Rh are effective for all nickel borides. On cyclohexene with slightly-polared olefinic group, Rh is also good for all nickel borides. But Cr and Co are only effective for P-2W and P-1 nickel borides respectively.     

Insights into structural,electronic, optical and thermoelectric properties of WB and WAlB: a first principle study

Detailed investigations on structural, electronic, optical and thermoelectric properties of WB and WAlB have been done by using a full-potential linearised augmented plane wave method. Different approximations have been used to treat the exchange–correlation potential. The PBEsol-GGA method is found to be the most suitable for WB and WAlB. The obtained values of the equilibrium structural parameters such as lattice constants, volume and bulk modulus are in good agreement with the available experimental and theoretical data. The results of electronic charge density plots show that WB has a strong covalent bond between B-B and an ionic bond between W-B. In case of WAlB, the distance between any two atoms is more than the corresponding interatomic distance in WB. The band structure and density of states around the fermi level suggest that WB has a metallic nature and WAlB has a semimetal-like character. The optical properties are determined and analysed in detail for the first time. The larger reflectivity in the low-energy region (infrared) indicates that these materials can be used as a coating material to remove solar heating. The effects of temperature on thermoelectric parameters are also studied for the first time. High value power factor and high thermal conductivity suggest that WB and WAlB are potential candidates for thermoelectric technological applications.     

First‐principles study of CrB4 as a high shear modulus compound

First‐principles calculations were carried out to investigate the synthesized orthorhombic CrB₄. Our calculations show that the shear modulus of orthorhombic CrB₄ is much higher than that of superhard WB₄. Moreover, its shear modulus is larger than its bulk modulus. Boron atoms in CrB₄ form a strong covalent cage which dramatically increases its mechanical strength. The calculated elastic constants imply that CrB₄ is elastically stable. The calculated density of states shows that CrB₄ is metallic. The appearance of pesudogap near the Fermi level means that CrB₄ is a stable compound. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)