Electrical conductivity, magnetoresistance, and hall coefficient in the course of bromination of graphite and ammonia absorption by potassium-graphite intercalation compounds

Abstract

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 , μ h , μ c ) for graphite-bromine intercalation compounds were determined as a function of the bromine content, Br C . As Br C increases, both n h and μ e increase, while n c and μ h decrease. The value of the product n h μ h increases with Br C , but n c μ 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 KC 8 were also determined as a function of NH 3 K , but the magnetoresistance was too small to be detected. The mean carrier concentration, n ̄ , and the mean carrier mobility, \\ ̄ gm, were estimated as a function of NH 3 K : n ̄ increases with the increase of NH 3 K , while \\ ̄ gm decreases with NH 3 K . It was found that the effect of the decrease of n ̄ is larger than that of the increase of \\ ̄ gm, resulting in the decrease of conductivity found with KC 8 as it is ammoniated. These results were attributed to backdonation of free electrons form the carbon π ∗ band to the intercalated layers, caused by the increase of the interlayer distance when potassium ions are solvated by ammonia molecules.