Bipolaron Hopping Conduction in Boron Carbides

Journal Article · Mon Sep 20 04:00:00 EDT 1999 · Physica Status Solidi

OSTI ID:12682

ASELAGE, TERRENCE L ^[1]; EMIN, D; MCCREADY, STEVEN S

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1. Sandia National Laboratories

The electrical conductivities of boron carbides, B{sub 12+x}C{sub 3{minus}x} with 0.1 < x < 1.7, between 300 and 1200K suggest the hopping of a nearly temperature-independent density of small (bi)polarons. The activation energies of the nobilities are low, {approx} 0.16 eV, and are nearly independent of the composition. At lower temperatures, conductivities have non-Arrhenius temperature dependencies and strong sensitivity to carbon concentration. Percolative aspects of low-temperature hopping are evident in this sensitivity to composition. Boron carbides' Seebeck coefficients are anomalous in that (1) they are much larger than expected from boron carbides' large carrier densities and (2) they depend only weakly on the carrier density. Carrier-induced softening of local vibrations gives contributions to the Seebeck coefficient that mirror the magnitudes and temperature dependencies found in boron carbides.

• Research Organization: Sandia National Labs., Albuquerque, NM (US); Sandia National Labs., Livermore, CA (US)
• Sponsoring Organization: US Department of Energy (US)
• DOE Contract Number: AC04-94AL85000
• OSTI ID: 12682
• Report Number(s): SAND99-2415J
• Journal Information: Physica Status Solidi, Journal Name: Physica Status Solidi
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTIVATION ENERGY
BORON CARBIDES
CARRIER DENSITY
ELECTRIC CONDUCTIVITY
POLARONS
SEEBECK EFFECT
TEMPERATURE RANGE 0400-1000 K