Electron Spin Resonance in Polycrystalline Graphite

Abstract

The electron spin resonance of polycrystalline graphite is shown to be due to charge carriers, as for single crystals. For lampblack-base graphite, the variation in g value with temperature agrees approximately with that for single crystal graphite if it is assumed that the spins effectively average out the anisotropic interactions by rapid intercrystallite diffusion. The magnitude and temperature dependence of the spin susceptibility are found to be in excellent agreement with McClure's theoretical predictions for the charge carriers in perfect graphite. Complications of measuring these materials are discussed, including effects of skin depth and microwave heating and the dependence upon crystallite size and sample purity. It is found that two types of impurities can affect the resonance; those which become ionized and shift the Fermi level, and large un-ionized atoms which do not shift the Fermi level but act as efficient scattering centers for shortening the spin—lattice relaxation time.

Synthesis, characterization and electrochemical properties of a novel triphosphate LiFe2P3O10

“…8) originating from unpaired spin electrons of carbon film are consistent with those of our sample shown in he insert of Fig. 8, and have the same temperature dependence [24]. At present, the factors governing the structure of the carbon produced by pyrolysis of organic compounds are poorly understood but the small D/G ratio between the intensities of the D and G band, respectively, is the signature for highly conductive carbon, which explains the good electrochemical performance, as it will be shown in the last section of this paper.…”

Modern and fossil charcoal: aspects of structure and diagenesis

“…We also conclude that the Quercus sample was formed at the highest temperature as it has the largest amount of free charge carriers. The latter, according to Singer and Wagoner [30], are located only in the graphite-like microcrystallites. The concentration of the paramagnetic centers was found to be 10 18 spin/mg (Table 3).…”

“…Unpaired electrons associated with organic molecules are called free radicals [21,27]. ESR can thus provide detailed information on the atomic structure of such materials, which includes graphite [30]. The presence of unpaired electrons in natural charcoals is well-documented [17,7].…”

Hybrid electron spin resonance and whispering gallery mode resonance spectroscopy of Fe3+in sapphire

“…26,27 The determination of g has been achieved in numerous materials, such GaAs, CdTe, InP, and graphite, and with various techniques. [28][29][30][31][32][33] In Al 2 O 3 crystals, electron spin resonance measurements have allowed the calculation of this factor for different ions in the microwave range. These measurements are summarized in Table II.…”