ELECTRICAL-CONDUCTIVITY, MAGNETORESISTANCE, AND HALL-COEFFICIENT IN THE COURSE OF BROMINATION OF GRAPHITE AND AMMONIA ABSORPTION BY POTASSIUM-GRAPHITE INTERCALATION COMPOUNDS

Electrical conductivity, transverse magnetoresistance, and Hall coefficient, both of graphite in the course of bromination and of potassium-graphite intercalation compounds (K-GICs) in the course of ammoniation, were determined. Concentrations and mobilities of holes and electrons (n(h), n(e), mu-h, mu-e) for graphite-bromine intercalation compounds were determined as a function of the bromine content, Br/C. As Br/C increases, both n(h) and mu-e increase, while n(e) and mu-h decrease. The value of the product n(h) mu-h increases with Br/C, but n(e) mu-e decreases. The increase of conductivity of graphite by bromination is confirmed to be a reflection of the increase in n(h), in agreement with the previous investigation by Marchand and Mathur. The conductivity and Hall coefficient of KC8 were also determined as a function of NH3/K, but the magnetoresistance was too small to be detected. The mean carrier concentration, nBAR, and the mean carrier mobility, muBAR, were estimated as a function of NH3/K: nBAR increases with the increase of NH3/K, while muBAR decreases with NH3/K. It was found that the effect of the decrease of nBAR is larger than that of the increase of muBAR, resulting in the decrease of conductivity found with KC8 as it is ammoniated. These results were attributed to backdonation of free electrons form the carbon pi* band to the intercalated layers, caused by the increase of the interlayer distance when potassium ions are solvated by ammonia molecules.