Verfeinerung des β-rhomboedrischen Bors

Abstract

For the interpretation of the electron paramagnetic resonance spectra of doped boron it is desirable to know the structure of boron. Based on the structure of fl-rhombohedral boron proposed in 1963-65 by Hoard and co-workers, the atomic coordinates were refined by means of intensity measurements of a boron single crystal. An R1 factor of 10.6% was obtained. EinleittmgMit Kohlenstoff dotiertes fl-rhomboedrisches Bor ist 1Gcherleitend und besitzt eine paramagnetische Elek-

Bor – elementare Herausforderung für Experimentatoren und Theoretiker

“…[96,97] Wie a-B kristallisiert es in der Raumgruppe R " 3 3m (Nr. 166), allerdings ist die rhomboedrische Elementarzelle (Abbildung 2 b, a = 1013.9 pm, a = 65.28) [96] erheblich größer als die von a-B.…”

“…[97] eine in Lit. [96] Erst kürzlich wurden weitere DFT-Rechnungen publiziert, die für den Grundzustand von b-B bei tiefen Temperaturen eine "symmetriegebrochene" Struktur vorhersagen, die eine stabile Anordnung von vollständig besetzten und vollständig freien Positionen in der triklinen Raumgruppe P1 aufweist. [105] In einer weiteren aktuellen, theoretischen Arbeit zur Stabilität von b-B bestätigen Ogitsu et al die stabilisierende Wirkung einer "makroskopischen Menge" intrinsischer Defekte und das Vorhandensein von zusätzlichen elektronischen Zuständen in der Bandlücke, im Sinne eines "selbstdotierenden" Halbleiters.…”

Lattice Vibrations, MIR and FIR Optical Properties of Boron and Icosahedral Boron-Rich Borides II. β-Rhombohedral Structure Group

“…The first description of the crystal structure of pure ^-rhombohedral boron is due to Hoard et al [7], It was confirmed by Geist et al [8] and determined by Callmer with high precision [9]. The most recent structural investigations were performed by Slack et al [10][11][12][13], According to the model of Hoard et al, the unit cell (rhombohedral description: a = 10.145(15) Ä, a = 75° 17 (8)'; hexagonal description: a = 10.944 Ä; c = 23.811 Ä; space group R 3 m) consists of 105 boron atoms occupying 16 independent positions, two of which are not completely occupied.…”

“…The most recent structural investigations were performed by Slack et al [10][11][12][13], According to the model of Hoard et al, the unit cell (rhombohedral description: a = 10.145(15) Ä, a = 75° 17 (8)'; hexagonal description: a = 10.944 Ä; c = 23.811 Ä; space group R 3 m) consists of 105 boron atoms occupying 16 independent positions, two of which are not completely occupied. Slack et al [11] found four additional partly occupied boron positions raising the number of B atoms per unit cell to 106.7.…”

VASP on a GPU: Application to exact-exchange calculations of the stability of elemental boron

“…The two relevant structures are the α-rhombohedral structure [9] (Pearson type hR12, with 12 atomic sites per primitive cell), which was initially believed [10] to be the stable form stable at low temperatures below T=1000K, and the more complex β-rhombohedral structure [11][12][13] (Pearson type hR105, with 105 atomic sites per primitive cell) which was initially believed to be stable at high temperatures, from T=1500K up to melting. Although uncertainty remains concerning the role of impurities [14], current opinion suggests α is only metastable, and β is the true equilibrium state for all temperatures, from melting down to T=0K [7].…”