Icosahedral boron-rich solids as refractory semiconductors

Conference · Wed Jul 01 04:00:00 EDT 1987

OSTI ID:6417783

Emin, D

Icosahedral boron-rich solids are refractory materials composed of twelve-atom boron-rich icosahedral units with strong intericosahedral linkages. These distinctive structures admit unusual electronic and thermal transport properties. Here the distinctive (three-center) bonding which underlies these materials is first described. Then it is shown how insulators, semiconductors and highly degenerate (metal-like) materials emerge from the same basic structure with appropriate substitutions. The electronic transport of the boron carbides is then addressed. The boron carbides are degenerate p-type semiconductors in which the charge carriers are diamagnetically aligned pairs of electrons which hop between icosahedra. Uniquely, this thermally activated hopping conductivity increases with increasing hydrostatic pressure. However, the Seebeck coefficient (thermoelectric power) is uncharacteristic of a degenerate semiconductor. Namely, the Seebeck coefficient is typically both large and an increasing function of temperature. In addition, despite the hardness and refractory character of these materials, their thermal conductivities can be surprisingly low with a glass-like temperature dependence. These features are manifestations of the distinctive structure and bonding of these solids. In fact, this novel mix of properties makes the boron carbides exceptionally good very-high-temperature p-type thermoelectric materials. Icosahedral boron-rich solids have additional potential as high temperature semiconductors. In particular, the wide-gap icosahedral boron-rich pnictides, B/sub 12/P/sub 2/ and B/sub 12/As/sub 2/, may be doped to form wide-gap refractory semiconductors. For example, replacement of the group V element with either a group VI or a group IV element is expected to yield n-type and p-type material, respectively. 41 refs.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6417783
• Report Number(s): SAND-86-2658C; CONF-870438-29; ON: DE87012103
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
360603 -- Materials-- Properties
ARSENIC COMPOUNDS
ARSENIDES
BIBLIOGRAPHIES
BORON ARSENIDES
BORON CARBIDES
BORON COMPOUNDS
BORON PHOSPHIDES
CARBIDES
CARBON COMPOUNDS
CRYSTAL STRUCTURE
DOCUMENT TYPES
ELECTRICAL PROPERTIES
PHOSPHIDES
PHOSPHORUS COMPOUNDS
PHYSICAL PROPERTIES
PNICTIDES
THERMAL CONDUCTIVITY
THERMODYNAMIC PROPERTIES
THERMOELECTRIC PROPERTIES