HALL-EFFECT IN THE NATURAL GLASSY-CARBON OF SCHUNGITES

The temperature dependences (80-500 K) of the Hall coefficient and the resistivity of samples of schungite of types I and III (schungite I a nd schungite III), as well as a commercial glassy carbon, with carbon contents equal to 98, 30, and 99.99%, respectively, are measured. The character of the dependences of the resistivity and its numerical valu es are similar to those observed in polycrystalline graphites with a h igh degree of disorder and in synthetic glassy carbon. Conversely, the Hall coefficient in the schungite samples, as in high-quality single crystals and n-type intercalated compounds of graphite, is found to be negative, small in magnitude, and weakly dependent on the temperature . At room temperature it is equal to 2.83 X 10(-2) and 0.305 cm(3)/C i n schungite I and schungite III, respectively, the Hall mobility of th e charge carriers in these materials is 8.0 and 9.2 cm(2)/V . s, and t he Hall carrier concentration is 2.2 X 10(20) and 2.0 X 10(19) cm(-3). (C) 1997 American Institute of Physics.