Electron spin resonance study by hot-pressed boron carbide

Conference · Tue Jan 01 04:00:00 EST 1985

OSTI ID:6305285

Venturini, E L; Azevedo, L J; Emin, D; Wood, C

Electron spin resonance (ESR) spectra are reported for four hot-pressed boron-rich boron carbide samples B/sub 1-x/C/sub x/ in the composition range 0.1less than or equal toxless than or equal to0.2. At 2K the spectra for all four compositions are characterized by a single Lorentzian absorption with a relatively narrow linewidth and free-electron g-value. The B4C ESR linewidth remains narrow between 2 and 295K, while the linewidth of the other three samples containing less carbon increases by a factor of 20 over this temperature range. Above 20K, the ESR signal in the latter three samples has a lineshape that cannot be described by a single Lorentzian, but can be explained as the sum of two Lorentzians with different linewidths, suggesting the presence of two distinct paramagnetic centers. The integrated intensities of the ESR signals in all samples follow a Curie law below 100K, and the Curie constant corresponds to spin concentrations of 2 to 3 x 10 Z per gram. While these values are in agreement with static magnetic susceptibility data for samples cut from the same hot-pressed element, they are approximately two orders of magnitude less than the carrier densities estimated form transport measurements. This suggests that the carriers are spinless bipolarons.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA); Jet Propulsion Lab., Pasadena, CA (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6305285
• Report Number(s): SAND-85-1524C; CONF-8508158-1; ON: DE86005439
• 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
CARRIER DENSITY
ELECTRON SPIN RESONANCE
FABRICATION
HOT PRESSING
MAGNETIC RESONANCE
MATERIALS WORKING
MEDIUM TEMPERATURE
PRESSING
RESONANCE
SPECTRA
TEMPERATURE DEPENDENCE
ULTRALOW TEMPERATURE