Thermopower and hall effect in silicon nitride composites containing thermally reduced graphene and pure graphene nanosheets

Composites consisting of dielectric silicon nitride (Si3N4) with diverse percentages of different graphene nanoreinforcements, such as graphene nanoplatelets (GNP) - 17 and 21 vol% - and reduced graphene oxide (rGO) sheets - 4 and 7 vol% - displayed thermopower effect. Maximum thermopower was observed for the rGO containing composites, which reached a peak Seebeck coefficient (S) of -26 mu V K-1 at 300 K, whereas GNP composites showed top S of +5 it mu V K-1 at the same temperature. Hall effect measurements indicated that current carriers were different in both composites, electrons for the rGO/Si3N4 (n-type conductor) and holes for the GNP/Si3N4 materials (p-type conductor) and also having similar to 1.4 times higher carrier concentration the first composites. The enhanced thermopower of the rGO/Si3N4 composites is attributed to the particular defective nature of rGO sheets, which presented edge defects and nanometer scale defect clusters as shown by the high resolution transmission electron microscope images - probably associated to both oxygen atoms remaining after GO reduction during spark plasma sintering and N doping from the Si3N4 matrix. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.