Anomalous electronic transport in boron carbides

Conference · Sun Jan 01 04:00:00 EST 1984

OSTI ID:6597058

Emin, D; Samara, G A; Wood, C

The boron carbides are composed of icosahedral units, B/sub 12/ and B/sub 11/C/sub 1/, linked together by strong intericosahedral bonds. With such distributions of icosahedral and intericosahedral compositions, boron carbides, B/sub 1-x/C/sub x/, are single phase over 0.1 less than or equal to x less than or equal to 0.2. We have examined the electronic transport properties of the boron carbides within this single-phase region. Results are inconsistent with conventional analyses of both itinerant and hopping transport. Most striking are Seebeck coefficients which are both large and rapidly increasing functions of temperature despite thermally activated dc conductivities. These results manifest the hopping of small bipolaronic holes between carbon-containing icosahedra that are inequivalent in energy and electron-lattice coupling strength. Under hydrostatic pressures up to approx. 25 kbar, the dc conductivities increase with pressure. This anomalous behavior for hopping conduction reflects the distinctive structure and bonding of these materials.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA); Jet Propulsion Lab., Pasadena, CA (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6597058
• Report Number(s): SAND-84-1449C; CONF-840879-1; ON: DE84015620
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
BORON CARBIDES
BORON COMPOUNDS
CARBIDES
CARBON COMPOUNDS
CHEMICAL COMPOSITION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
HALL EFFECT
PHYSICAL PROPERTIES
PRESSURE DEPENDENCE
QUANTITY RATIO
SEEBECK EFFECT
TEMPERATURE DEPENDENCE