First-principles calculation of 11B solid-state NMR parameters of boron-rich compounds I: the rhombohedral boron modifications and B12X2 (X = P, As, O)

This study reports on solid-state nuclear magnetic resonance spectra under magic angle spinning conditions of the rhombohedral structures α-B and B12P2 together with parameter sets from first principles calculations on α-B and B12X2 (X = P, As, O).

Rhombohedral Boron Nitride Epitaxy on ZrB2

<div>Epitaxial rhombohedral boron nitride films were deposited on ZrB₂(0001)/4H-SiC(0001) by chemical vapor deposition at 1485 °C from the reaction of triethylboron and ammonia and with a minute amount of silane (SiH₄). X-ray diffraction (XRD) φ-scans yield the epitaxial relationships of 𝑟−𝐵𝑁(0001)∥𝑍𝑟𝐵2(0001) out-of-plane and 𝑟−𝐵𝑁(1120)∥𝑍𝑟𝐵2(1120) in-plane. Cross-section transmission electron microscopy (TEM) micrographs showed that epitaxial break down of r-BN film occurs approximatively after 10 nm, above which epitaxial growth proceeds only in limited area up to 80 nm of film thickness. Both XRD and TEM demonstrate the formation of carbon- and nitrogen-containing cubic inclusions at the ZrB₂ surface. Quantitative analysis from X-ray photoelectron spectroscopy of the r-BN films shows B/N ratios between 1.30 to 1.20 and an O content of 3 to 4 at.%. Plan-view scanning electron microscopy (SEM) images reveal a surface morphology where an amorphous material comprising B, C, and N is surrounding the epitaxial twinned r-BN crystals. SiH₄ exposure prior to growth was found to reduce the amount of the amorphous phase on the surface. Defects such as pitting were also observed on the ZrB₂ template surface.</div><div><br></div>

Rhombohedral Boron Nitride Epitaxy on ZrB2

<div>Epitaxial rhombohedral boron nitride films were deposited on ZrB₂(0001)/4H-SiC(0001) by chemical vapor deposition at 1485 °C from the reaction of triethylboron and ammonia and with a minute amount of silane (SiH₄). X-ray diffraction (XRD) φ-scans yield the epitaxial relationships of 𝑟−𝐵𝑁(0001)∥𝑍𝑟𝐵2(0001) out-of-plane and 𝑟−𝐵𝑁(1120)∥𝑍𝑟𝐵2(1120) in-plane. Cross-section transmission electron microscopy (TEM) micrographs showed that epitaxial break down of r-BN film occurs approximatively after 10 nm, above which epitaxial growth proceeds only in limited area up to 80 nm of film thickness. Both XRD and TEM demonstrate the formation of carbon- and nitrogen-containing cubic inclusions at the ZrB₂ surface. Quantitative analysis from X-ray photoelectron spectroscopy of the r-BN films shows B/N ratios between 1.30 to 1.20 and an O content of 3 to 4 at.%. Plan-view scanning electron microscopy (SEM) images reveal a surface morphology where an amorphous material comprising B, C, and N is surrounding the epitaxial twinned r-BN crystals. SiH₄ exposure prior to growth was found to reduce the amount of the amorphous phase on the surface. Defects such as pitting were also observed on the ZrB₂ template surface.</div><div><br></div>

Phase Evolution and Critical Temperature of MgB2 Superconductor Made of β-Rhombohedral Boron with Temperature Sintering Variation

We report the phase formation and electrical resistivity of MgB2 superconductor samples. Method of synthesis was conventional solid-state reaction employing crystalline β-rhombohedral boron (B) and magnesium (Mg) with a stoichiometric ratio of Mg:B=1:2. The two precursors were mixed and sintered at various temperatures from 600°C to 900°C for an hour. All samples were characterized employing XRD, SEM, and Cryogenic Magnetometer. It is shown that the MgB2 phase begins to form at a sintering temperature of 700°C. The highest peak intensity of the MgB2 phase was observed in a sample sintered at 900°C indicates the largest fraction of the superconducting phase among all synthesized samples. Electrical resistivity values were carried out to investigate the superconducting properties of the samples. It is also shown the samples sintered at a temperature of 800°C and 900°C possess superconducting properties with a critical temperature of ~ 43 K