12008-32-1Relevant articles and documents
Characterization of the electronic properties of YB4 and YB 6 using 11B NMR and first-principles calculations
J?ger,Paluch,Wolf,Herzig,Zoga?,Shitsevalova,Paderno
, p. 232 - 238 (2004)
Two compounds, tetragonal YB4 and cubic YB6, have been investigated by electric-field gradient (EFG) and Knight shift measurements at the boron sites using the 11B nuclear magnetic resonance (NMR) technique and by performing first-principles calculations. In YB6 11B (I=3/2) NMR spectra reveal patterns typical for an axially symmetric field gradient with a quadrupole coupling frequency of νQ=600±15kHz. In the second boride (YB4) three different EFGs were observed corresponding to the three inequivalent crystallographic sites for the boron atoms (4h, 4e, and 8j). They correspond to: νQ(4h)=700±30kHz with an asymmetry parameter η=0.02±0.02, νQ(4e)=515±30kHz, η=0.00+0.02/-0.00, and νQ(8j)=515±40kHz, η=0.46±0.08. The Knight shifts measured by magic-angle spinning (MAS) NMR at room temperature are very small being 0.6±8 and -1±8ppm for YB4 and YB6, respectively. For the theoretical calculations structure optimizations were performed as a first step. For the obtained structural parameters the EFGs were computed within the local-density approximation. Very satisfactory agreement between experimental and theoretical results is obtained both for the structural parameters and the B EFGs, thus confirming the underlying structural models. In addition to the EFGs, band structures, densities of states, and valence-electron densities are presented and the bonding situation in the two yttrium borides is discussed. The band-structure results are compatible with the very low values for the Knight shifts mentioned above.
Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1- xYxB12 and Zr1- xUxB12
Akopov, Georgiy,Mak, Wai H.,Koumoulis, Dimitrios,Yin, Hang,Owens-Baird, Bryan,Yeung, Michael T.,Muni, Mit H.,Lee, Shannon,Roh, Inwhan,Sobell, Zachary C.,Diaconescu, Paula L.,Mohammadi, Reza,Kovnir, Kirill,Kaner, Richard B.
, p. 9047 - 9062 (2019)
Single-phase metal dodecaboride solid solutions, Zr0.5Y0.5B12 and Zr0.5U0.5B12, were prepared by arc melting from pure elements. The phase purity and composition were established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and 10B and 11B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to Zr1-xYxB12 were studied and it was found that carbon causes fast cooling and as a result rapid nucleation of grains, as well as "templating" and patterning effects of the surface morphology. The hardness of the Zr0.5Y0.5B12 phase is 47.6 ± 1.7 GPa at 0.49 N load, which is ～17% higher than that of its parent compounds, ZrB12 and YB12, with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr0.5U0.5B12 is ～54% higher than that of its UB12 parent. The dodecaborides were confirmed to be metallic by band structure calculations, diffuse reflectance UV-vis, and solid-state NMR spectroscopies. The nature of the dodecaboride colors - violet for ZrB12 and blue for YB12 - can be attributed to charge-transfer. XPS indicates that the metals are in the following oxidation states: Y3+, Zr4+, and U5+/6+. The superconducting transition temperatures (Tc) of the dodecaborides were determined to be 4.5 and 6.0 K for YB12 and ZrB12, respectively, as shown by resistivity and superconducting quantum interference device (SQUID) measurements. The Tc of the Zr0.5Y0.5B12 solid solution was suppressed to 2.5 K.
Large crystal structure distortion in DyB6 studied by X-ray diffraction
Granovsky,Markosyan
, p. 529 - 531 (2008/10/08)
A large magnetoelastic coupling induces a lattice distortion of a rhombohedral type in DyB6. Below the quadrupolar ordering temperature TQ=31K the cubic and the distorted phases coexist. The cubic phase disappears at 23K, which was identified as the magnetic ordering point TN. In the magnetic phase the distortion (dl/l)111 increases monotonically with decreasing temperature and reaches the value of 9 × 10-3 at 8 K, which is one of the largest value known for cubic compounds.
