New method for preparing graphene by peeling graphite and facile fabrication of bulk Bi0.45Sb1.55Te3.02/graphene composites with dense texture and high ZT

摘要

We report a new method for peeling graphite to graphene, with which we develop a facile procedure for the fabrication of bulk Bi0.45Sb1.55Te3.02/graphene by pushing thin graphite foils into pressed Bi0.45Sb1.55Te3.02 powders and then foliated into graphene under pressure and high direct current (up to 1000 A). The pushing force results from the huge repulsive Coulomb force between the layers in the graphite foil. The Coulomb force arises from electron agglomeration as a result of the Lorentz force that the large direct-current-produced magnetic field applies on the moving electrons in the graphite foil. The incorporated graphene sheets act as growth templates for the Bi0.45Sb1.55Te3.02 grains. Consequently, fast grain growth and a densely textured microstructure with laminates were observed in the Bi0.45Sb1.55Te3.02/graphene bulk. By combining direct current and applied pressure, anisotropic textures were obtained, with the laminates oriented mostly along the axial direction. Since the laminates can filter low-energy carriers and scatter long-distance phonons, an increased Seebeck coefficient, decreased thermal conductivity, and a consequential 25% enhancement in the figure of merit, ZT (1.40 at 90.9 degrees C), were observed in the direction along which pressure was applied. This work suggests that graphene can be utilized as a template to rapidly grow single crystals of materials with similar crystal structures, as well as to adjust the textures of materials. This facile method is expected to be applicable in the fabrication of bulk semiconductor or graphene/alloy composites.