Investigation of graphene dispersion on thermoelectric, magnetic, and mechanical properties of p-type Bi0.5Sb1.5Te3 alloys

In this research, polycrystalline p-type Bi0.5Sb1.5Te3 (BST)/x-wt% graphene (x = 0, 0.05, 0.1 and 0.2 wt%) composite bulks were fabricated to systematically investigate the effect of graphene content on thermoelectric, as well as magnetic and mechanical properties. The peaks corresponding to the D, G and 2D bands of graphene were clearly identified with Raman spectroscopy, and revealed that graphene was well dispersed in the BST matrix. The bulk fracture surfaces displayed randomly distributed grains and a progressive decrease in grain size, with increasing graphene content in the composite samples. A dramatic reduction in thermal conductivity of about 10%, and 12% was achieved for the 0.1, and 0.2 wt% graphene dispersed Bi0.5Sb1.5Te3 samples, respectively, due to the strong scattering of phonons at interfaces and fine grain boundaries. Thanks to the adequate power factor and the reduction in thermal conductivity by the incorporated graphene, the 0.1 wt% graphene dispersed Bi0.5Sb1.5Te3 sample showed the highest ZT value among all samples. Interestingly, a transformation from diamagnetic to para/ferro magnetic properties was observed after graphene incorporation, using magnetic hysteresis loops. Vickers hardness was also greatly improved, from 84.1 Hv to 103.8 Hv, and compressive strength was also increased. It was concluded that enhanced mechanical properties of the Bi0.5Sb1.5Te3 alloys was due to the strengthening effect of hierarchically structured graphene and reduced grain size.