On the Conductivity Mechanism of β‐Rhombohedral Boron

Abstract

Electron and hole trapping levels of high density of states determine essentially the conductivity mechanism of P-rhombohedra1 boron. The ionization energy of trapped electrons is much greater than that of trapped holes; so, up to high temperatures, the electrons do not appreciably contribute to the charge transport. From electrical conductivit,y and thermoelectric power a t higher temperatures one obtains the activation energy of the hole mobility (0.19 eV). At low temperatures hopping within the hole trapping level seems t o be the prevailing conductivity mechanism.Haftniveaus groBer Zustandsdichte fur Elektronen und Locher sind fur den Leitungsmechanismus des P-rhomboedrischen Bors von entscheidender Bedeutung. Die Aktivierungsenergic der eingefangenen Elektronen ist wesentlich groBer als die der eingefangenen Locher, so daB die Elektronen bis z u sehr hohen Temperaturen nicht merklich zum Ladungstransport beitragen. Ails elektrischer Leitfahigkeit und Thermokraft bei heheren Temperaturen erhalt man eine Aktivierungsenergie der Locherbeweglichkeit von 0,19 eV. Bei tiefen Temperaturen scheinen hopping-Prozesse inncrhalb des Locherhaftniveaus den dominierenden Leitungsmechanismus darzustellcn.

Phase transition in β-rhombohedral boron near 550 K

“…2b) [9], electrical conductivity ( Fig. 3) [10,11], probably Seebeck coefficient [10] (Fig. 3, insert), optical absorption ( Fig.…”

Evidence of the Superposition of Drude Type and Hopping Type Transport in Boron-Rich Solids

“…The integral in Eq. [2] was solved numerically. From the apparently great number of model parameters only the plasma frequency of the Drude model and factor A of the hopping model turned out to be essential.…”

“…Below it will be shown that a simulation of the spectra is possible when a dynamical conductivity resulting from a superposition of hopping type and free carrier type charge transport is assumed. The model used is based on the dominating hopping mechanism of the DC conductivities, which was first demonstrated for -rhombohedral boron (2) and has meanwhile been confirmed for this and many other boron-rich solids by various authors, on the hopping character of AC conductivity demonstrated in particular for boron carbide (3), and on experimental results of transport properties like, for example, magnetoresistance, whose interpretation requires the assumption of band-type free carriers.…”

First-principles study of the crystal and electronic structures of α-tetragonal boron

“…They suggested that the conduction may be prompted by the hopping process, as seen in b-rh boron [7], or just by simple thermal activation. The existence of band gap was also confirmed by electron energy loss spectroscopy (EELS) [32].…”

“…There has been a lot of research into the properties of a-and b-rhombohedral (a-rh, b-rh) boron, revealing that these materials are p-type semiconductors under normal pressure [6,7]. In 2001, it was discovered that b-rh boron becomes superconductive under high pressure [8], and in 2007 a-rh was also reported to become superconductive under high pressure [9,10].…”